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Ozone Depletion Hearing Written Testimony November 15, 1991
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61
5
6
2
SENATE COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION
Witness List*
Hearing on
Global Change Research: Ozone Depletion and Its Impacts
Friday, November 15, 1991, 9:30 a.m.
in room SR-253 of the Russell Senate Office Building
Roundtable Discussion Participants:
Dr. Daniel L. Albritton, Director, Aeronomy Lab, National
Oceanic and Atmospheric Administration, Boulder, CO
80303
Dr. Stephen Anderson, Director, Technology Transfer and
Industry Program, U.S. Environmental Protection Agency,
Washington, DC 20460
Dr. Margaret L. Kripke, Chairperson, Department of
Immunology, M. D. Anderson Cancer Center, University of
Texas, Houston, TX 77030
Dr. Ari Patrinos, Acting Director, Environmental Sciences
Division, ER-74, U.S. Department of Energy, Washington,
DC 20585
Dr. Alan H. Teramura, Professor and Chair, Department of
Botany, University of Maryland, College Park, MD
20742
Dr. Shelby Tilford, Director of Earth Science and Application
Division, National Aeronautics and Space Administration,
Washington, DC 20546
Dr. Jan C. van der Leun, Institute of Dermatology, University
Hospital Utrecht, Heidelberglaan 100, NL-3584 CX
Utrecht, The Netherlands
-2-
Dr. Robert T. Watson, Branch Chief, Upper Atmosphere Research
Tropospheric Chemistry, Earth Science and Space
Applications Division, National Aeronautics and Space
Administration Headquarters, Washington, DC 20546
Dr. Susan Weiler, Executive Director of the American Society
of Limnology and Oceanography, Department of Biology,
Whitman College, Walla Walla, WA 99362
Dr. Robert Worrest, Program Manager, Stratospheric Ozone
Research Program, U.S. Environmental Protection Agency,
Washington, DC 20460
*Not Necessarily in Order of Appearance
UTMDACÇ/IMMUNOL
TEL No.17137941322
NOV 14,91 13:28
1
EFFECTS OF ULTRAVIOLET-B RADIATION ON IMMUNE RESPONSES
OF MICE AND MEN
Margaret L. Kripke, Ph.D.
Vivian L. Smith Chair in Immunology
Professor and Chairman
Department of Immunology
University of Texas M. D. Anderson Cancer Center
Houston, Texas
United States Senate
Committee on Commerce, Science, and Transportation
Hearing on
Global Change Research: Ozone Depletion and Its Impacts
Friday, November 15, 1991
UTMDACC/IMMUNOL
TEL No. 17137941322
Nov 14,91 13:28 No. 002 P.03
2
INTRODUCTION
The immune system is the body's primary defense mechanism
against infectious diseases. In addition to providing protection against
bacterial, viral, fungal, and parasitic infections, the immune system
also protects against the development of certain types of cancer,
particularly those associated with cancer viruses and UV radiation (1).
Any impairment of immune function can jeopardize health by increasing
susceptibility to infectious diseases, increasing the severity of
infections, or delaying recovery from infections. In addition, impaired
immune function can increase the incidence of certain cancers,
particularly cancers of the skin (2).
Research carried out with laboratory animals over the past 15
years has demonstrated that exposure of the skin to UV-B radiation can
suppress certain types of immune responses (3). These include
rejection of UV-induced skin cancers (4) and melanomas (5): contact
allergy reactions to chemicals (3); delayed-type hypersensitivity (DTH)
responses to microbial and other antigens (6); and phagocytosis and
elimination of certain bacteria from lymphoid tissues (6).
IMMUNOSUPPRESSIVE EFFECTS OF UVB RADIATION IN ANIMALS
Effects related to skin cancer. The realization that UV-B
radiation can affect the immune system came from studies on the
effects of UV radiation in experimental animals. Many years ago, we
discovered that exposing mice to UV rays caused a systemic change in
their immune system that rendered them incapable of resisting the
development and spread of UV-induced skin cancers (4). We now know
that the systemic change brought about by UVB irradiation involves the
production of suppressor lymphocytes. These white blood cells are part
of the Immune system and are responsible for regulating the magnitude
and duration of an immune response. The suppressor lymphocytes
present in mice exposed to repeated doses of UV-B radiation prevent
the development of an immune response against UV-induced skin
cancers. Thus, these suppressor lymphocytes impair the body's natural
defense mechanisms against skin cancer development (7).
Effects on other immune reactions. In trying to determine how
exposing the skin to UV radiation could alter a systemic immune
response, it was discovered that UV-B radiation can suppress other
types of Immune reactions, in addition to tumor rejection (3). For
UTMDACC/IMMUNOL
TEL No 17137941322
NOV
example, mice treated with very low (suberythemal) doses of UV-B
radiation fail to make a contact allergy reaction to chemicals applied
through the irradiated skin. Instead, suppressor lymphocytes are
produced. The mechanism involves an alteration in the activity of an
immune cell present in the skin, the epidermal Langerhans cell, which
normally picks up foreign substances in the skin, carries them to the
lymph node, and stimulates the lymphocytes to initiate an immune
reaction. Exposure of Langerhans cells to UV radiation renders them
unable to stimulate the appropriate type of lymphocytes and instead,
suppressor lymphocytes are activated (8).
With higher doses of UV-B, UV-irradiated mice lose their ability
to respond to chemicals applied through unexposed skin (3). They also
have a decreased delayed hypersensitivity response to a variety of
antigens, including those of bacteria, viruses, and fungi (6). The
delayed hypersensitivity response is a lymphocyte-mediated immune
reaction that contributes to the destruction and elimination of various
microorganisms. Suppression of this response by UV irradiation is also
mediated by suppressor lymphocytes. This systemic effect of UV
irradiation has been demonstrated to occur in several species of
animals, to be produced with relevant doses of natural sunlight, to be
due mainly to wavelengths in the UV-B region of the spectrum, and to
Increase in proportion to increasing doses of UV radiation (3). The
effect is thought to be due to the release of chemical mediators from
skin cells (keratinocytes) damaged by UV rays.
Effects on infectious diseases. The finding that UV radiation can
suppress certain lymphocyte-mediated immune reactions raised the
possibility that immunity to infectious agents might also be impaired
in UV-irradiated animals. Some disease-causing organisms, such as
Leishmania, Malaria, and Schistosoma, and the leprosy bacillus, gain
entry into the body through the skin. It was therefore possible that the
entry of such organisms through UV-damaged skin might lead to
activation of suppressor lymphocytes instead of a protective immune
response. Other infectious agents, including viruses, bacteria, and
fungi, produce diseases within the skin, and in addition, many
organisms are normally controlled by the delayed hypersensitivity type
of immune response. In these instances, the systemic immune
suppression resulting from UV-B-irradiation could increase the
severity of the disease process and prevent the development of
immunity against reinfection.
4
To date, these possibilities have been tested in only a few animal
models of infectious diseases (Reviewed in 6). The infectious agent
that has been studied most extensively is herpes simplex virus (HSV).
It is well known that UV radiation can trigger active herpes virus
infections in humans and experimental animals that harbor latent virus.
Mice exposed to low doses of UV radiation before inoculation of HSV
showed an increase in the severity of skin lesions and systemic
disease. In addition, low doses of UV radiation suppressed the
induction of delayed hypersensitivity to viral antigens and resulted in
the production of suppressor lymphocytes.
In several murine infectious disease models, mice were given low
doses of UV radiation to impair the function of epidermal Langerhans
cells and then infected with various microorganisms at the site of UV
irradiation. Infection of mice with Leishmania decreased the resultant
delayed hypersensitivity response to this parasite and diminished
immunity to reinfection. However, these low doses of UV radiation had
no effect on the rate of infection with either Leishmania or
Schlstosoma parasites, nor did they affect the development of the
delayed hypersensitivity response to a fungus, Candida albicans, or a
bacterium Mycobacterium bovis injected subcutaneously at the
irradiated site. The ability of the mice to clear mycobacteria from the
lymphoid tissues was reduced, however, resulting in a prolonged and
more severe infection.
Mice given doses of UV radiation sufficient to cause systemic
immune suppression are unable to make a delayed hypersensitivity
response to candida or mycobacteria injected at a non-irradiated site.
Furthermore, such mice are more susceptible to the lethal effects of an
intravenous inoculation of candida, and their ability to control
mycobacterial infection is greatly reduced, probably because the
macrophages from such animals have reduced phagocytic activity. The
progression of chronic infection of mice with Mycobacterim
lepraemurium is also accelerated in UV-irradiated mice. There is
evidence to suggest that some of these effects of UV irradiation also
result from the action of chemical mediators released from UV.
irradiated keratinocytes.
IMMUNOSUPPRESSIVE EFFECTS OF UV RADIATION IN HUMANS
There is increasing evidence that humans are also subject to the
immunosuppressive effects of UV radiation ( Reviewed in 9). For
5
example, exposing human skin to UV-B radiation damages the
Langerhans cells and changes the immunologic function of the skin in a
manner similar to that described in mice. Also, several investigators
have documented changes in the proportions of different types of white
blood cells in people exposed to natural and artificial sources of UV
radiation.
Of great interest in this regard are recent studies by Streilein
and colleagues demonstrating that applying a contact allergy-producing
chemical to skin given suberythemal doses of UV radiation fails to
induce the expected immune response in about 40% of normal subjects;
in patients who have had one or more skin cancers, the proportion of
non-responsive individuals approaches 100% (10). This study
demonstrates that humans are subject to at least one of the forms of
immunosuppression identified in mice and suggests, in addition, that
susceptibility to UV-induced immunosuppression constitutes a risk
factor for the development of skin cancer. A second study (11)
compared the same immunosuppressive effect of UV radiation in
different ethnic groups having different amounts of skin pigmentation.
There were no differences in the immunosuppressive effect of UV
radiation in persons with white, brown, or black skin, indicating that
pigmentation is not protective against this form of UV-induced
immunosuppression. Thus, the population at risk of immunological
damage from UV radiation is much larger than that at risk of developing
skin cancer. At present, the significance of this immunological
alteration for infectious diseases in humans is unknown.
CONCLUSIONS
The immunosuppressive effects of UV-B radiation in laboratory
animals are well documented. There is also evidence that UV-induced
immunosuppression can worsen some infectious disease processes in
animal models Recent studies have shown adverse effects of UV
radiation on immune cells and on some immune functions in humans,
and these effects probably contribute to the induction of skin cancers
in susceptible individuals. However, it is not known whether the
immunological effects of UV radiation can contribute to increases in
the incidence or severity of infectious diseases in humans. This is the
most critical unanswered question in attempting to assess the impact
of ozone depletion on human health. Infectious diseases constitute an
enormous public health problem worldwide, and any factor that reduces
immune defenses, thereby increasing the incidence or severity of
6
infectious diseases, is likely to have a devastating impact on human
health. Studies suggesting that skin pigmentation is not protective
against UV-induced immunosuppression imply that this effect of UV
irradiation is not limited to the Caucasian population at risk of
developing skin cancer, but may extend to other ethnic groups, as well.
Another urgent problem comes from studies in laboratory animals
suggesting that some commercial sunscreen preparations that protect
against sunburn do not protect against the immunosuppressive effects
*
of UV radiation. If this is true, then the concept that individuals can
protect themselves from the hazardous effects of sunlight exposure by
the use of currently available sunscreens must be reevaluated.
*NOU
Much more information is also needed on the mechanisms of UV-
Jare
induced immunosuppression if we wish to be able to predict the
immunological consequences of increased exposure to UV-B radiation.
Not
the safein
in
Testimony of Stephen O. Andersen, Senate Committee on Commerce,
Science, and Transportation: Hearing on Global Change Research:
Ozone Depletion and Its Impacts, Friday, November 15, 1991
My name is Stephen O. Andersen. I am appearing as Co-
Chairman of the United Nations Environment Programme (UNEP
Technical and Economics Assessment. I am not representing the
Environmental Protection Agency. I am Director of Technology
Transfer and Industry Programs in the Global Change Division,
Office of Atmospheric and Indoor Air Programs, Air and Radiation,
of the U.S. Environmental Protection Agency.
The 1991 UNEP Technical and Economic Assessment was
undertaken by over 240 experts from 37 countries.¹ Hundreds of
additional experts served as advisors to the six committees and
as peer reviewers. These include U.S. and foreign industry
representatives, government representatives and international
science experts.
The Assessment describes current uses and quantities of
controlled substances, estimates the technically feasible
phaseout dates, estimates the quantity and time period for use of
transitional substitutes, and specifically describes the
implications of a 1997 phaseout. The assessment will not be
final until December but I am pleased to report on the consensus
findings and conclusions as reported in the Executive Summary:
Since 1986 there has been forty percent worldwide drop in
the production of CFCs--this is faster than predicted by the
1989 Assessment and faster than the controls of the Montreal
Protocol.
Several multinational companies are eliminating the use of
ozone-depleting substances far faster than even the most
stringent regulation. By January 1992 the first companies
will have eliminated the use of CFC-113 solvents in all
their worldwide operations; halon and CFC recycling will be
accepted worldwide; the first HFC-134a automobile air
conditioners will be commercialized, and many other ozone-
safe technologies will be available. The first HFC-134a
domestic refrigerators will be commercialized in 1992.
'Australia, Austria, Belgium, Brazil, Canada, Chile, China,
Denmark, Ecuador, Egypt, France, Germany, India, Indonesia,
Italy, Japan, Jordan, Kenya, Korea, Malaysia, Mexico,
Netherlands, New Zealand, Nigeria, Norway, Papua New Guinea,
Singapore, Sweden, Switzerland, Trinidad and Tobago, Tunisia,
Uganda, USSR, United Kingdom, United States, Venezuela, and
Yugoslavia.
Testimony of Stephen O. Andersen (continued)
Page 2 of 2
The international fire protection community has virtually
eliminated halon emissions caused by discharge testing and
training and service emissions have been drastically
reduced. Educational programs are proving successful as
users move to alternative fire protection measures, where
feasible, and voluntarily limit halon use to essential
applications.
It is technically feasible in developed countries to phase
out production of CFCs and halons by 1997 or earlier, 1,1,1-
trichloroethane as early as 1995, and carbon tetrachloride
in the vast majority of applications by 1995.
These rapid phaseout schedules require that the results of
the toxicity tests, environmental assessments, and risk
analyses conclude that the alternatives HCFC-22, HCFC-123,
HCFC-124, HCFC-141b, HCFC-142b, and HFC-134a can be safely
used for refrigeration, air conditioning, insulating foam,
and for some aerosol, sterilization and minor solvent uses;
that these HCFCs and HFC are environmentally acceptable; and
that they are commercially available in adequate quantities.
The halon phaseout is contingent on the use of recycled
halons as the prime supply of those agents.
There is no perfect substitute. Each substitute has
difficult trade-offs in ODP of transitional substances, GWP,
energy efficiency, and toxicity. Trade-offs can be
minimized and mitigated by recycling and bank management, by
limiting the use of transitional or high GWP options to only
where necessary, and by limiting occupational exposures.
For small uses, there are no substitutes yet, but the
Technical and Economic Assessment is optimistic.
It is critical to successful phaseout for developing
countries that technologies are available, that supporting
technical assistance and training is provided, and that
adequate financial assistance is forthcoming. Several
developing countries are entering into innovative technology
cooperation projects. For example, Mexico has announced a
goal of phasing out controlled substances on the same
schedule as developed countries. The Mexican government and
industry are making partnerships with the U.S. Environmental
Protection Agency (EPA), the Industry Cooperative for Ozone
Layer Protection (ICOLP), and Northern Telecom to phase out
solvents. Similar partnerships may speed elimination in
other developing countries.
** REPORT OF THE TECHNOLOGY AND ECONOMICS ASSESSMENT PANEL **
** NOVEMBER 1991 **
2-2
SENATE COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION
Witness List*
Hearing on
Global Change Research: Ozone Depletion and Its Impacts
Friday, November 15, 1991, 9:30 a.m.
in room SR-253 of the Russell Senate Office Building
Sen. Gore
Roundtable Discussion Participants:
statement.
No
Dr. Daniel L. Albritton, Director, Aeronomy Lab, National
Oceanic and Atmospheric Administration, Boulder, CO
80303
2
Dr. Stephen Anderson, Director, Technology Transfer and
Industry Program, U.S. Environmental Protection Agency,
Washington, DC 20460
3 Dr. Margaret L. Kripke, Chairperson, Department of
Immunology, M. D. Anderson Cancer Center, University of
Texas, Houston, TX 77030
4 Dr. Ari Patrinos, Acting Director, Environmental Sciences
Division, ER-74, U.S. Department of Energy, Washington,
DC 20585
5
Dr. Alan H. Teramura, Professor and Chair, Department of
Botany, University of Maryland, College Park, MD
20742
Nonement Dr.
Shelby Tilford, Director of Earth Science and Application
Division, National Aeronautics and Space Administration,
Washington, DC 20546
6
Dr. Jan C. van der Leun, Institute of Dermatology, University
Hospital Utrecht, Heidelberglaan 100, NL-3584 CX
Utrecht, The Netherlands
6 a Executive Summary Scientific
Desessment of StRAtospheric
zone 1991
-2-
7
Dr. Robert T. Watson, Branch Chief, Upper Atmosphere Research
Tropospheric Chemistry, Earth Science and Space
Applications Division, National Aeronautics and Space
Administration Headquarters, Washington, DC 20546
8
Dr. Susan Weiler, Executive Director of the American Society
of Limnology and Oceanography, Department of Biology,
Whitman College, Walla Walla, WA 99362
9
Dr. Robert Worrest, Program Manager, Stratospheric Ozone
Research Program, U.S. Environmental Protection Agency,
Washington, DC 20460
*Not Necessarily in Order of Appearance
STATEMENT OF SENATOR ALBERT GORE, JR.
COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION
HEARING ON OZONE DEPLETION AND ITS IMPACTS
FRIDAY, NOVEMBER 15, 1991
Good morning. Today, the Commerce Committee will
examine the latest information on the damage we are doing to
the earth's protective ozone layer and what it means to us,
our health, our food supply, and our global environment.
On October 22, the United Nations Environmental
Programme released the executive summary of a report
entitled, "A Scientific Assessment of Stratospheric Ozone,
1991." This is one of three parts of a UNEP assessment of
ozone depletion which is due to be released in its entirety
early next year. This is the second such assessment done
since the Montreal Protocol on Substances that Deplete the
Ozone Layer was signed in 1987. The Montreal Protocol called
for these international assessments so that policymakers
would have the information they need to revise and update the
Protocol as new scientific data came available. Like the
first assessment released in 1989, this new report includes
disturbing new data indicating that ozone depletion is even
more serious than we thought.
Many of our witnesses today were involved in writing the
1989 assessment, which concluded that ozone depletion was
occurring much faster than most models predicted. As a
direct result of that report, the Montreal Protocol was
amended to require a more rapid phase-out of CFCs, halons,
and other ozone-depleting chemicals.
According to the report released this year on
October 22, ozone depletion is occurring even faster than we
thought in 1989. And it is occurring over more of the globe,
throughout most of the year. New data provides clear
evidence that ozone depletion is occurring not only in the
winter, but in the spring and summer as well--when plants,
animals, and people are most vulnerable. This ozone
depletion is occurring not only in the Antarctic Ozone Hole,
but also in the Arctic and at mid-latitudes, over our heads
here in the United States. Worst of all, it appears that
ozone depletion is accelerating.
According to the data, the ozone layer over the U.S. is
thinning between 3 and 5 percent per decade. According to
Sherwood Rowland, who testified before this Committee in
April, the ozone layer has thinned about 10 percent since the
1960s. This is significant; it's widespread; and it will
have major impacts on the environment and on people
worldwide.
We are only now determining what those impacts will be.
Unfortunately, there has been little research on the impacts
of ozone depletion and increased ultraviolet radiation.
Until recently, much of the data on the impacts of
ultraviolet radiation has been preliminary and incomplete.
Fortunately, there have been a number of good, solid studies
completed in the last year or two that give us a clearer
picture. The new UN report effectively summarizes that new
research. It is provides the most thorough assessment to
date of the impacts of ozone depletion
And the news is not good. Researchers here today have
discovered that increased ultraviolet radiation will reduce
the quantity and quality of crops, increase skin cancer,
suppress the human immune system, and disrupt marine
ecosystems. According to the report, a 10 percent decrease
in ozone will lead to between 1.6 and 1.75 million additional
cases of cataracts per year world-wide and at least 250,000
additional cases of skin cancer per year. There are
indications that increased ultraviolet radiation suppresses
the human immune system that protects us from disease. It is
now clear that ozone depletion will directly affect the
health of millions and millions of people.
Ozone depletion will have major impacts on ecosystems as
well. Trees, plants, plankton all seem vulnerable to
ultraviolet radiation. And no doubt, there will be other
serious consequences, many which we cannot yet anticipate,
due in part to a lack of research.
Last year, the Federal government spent almost
$1 billion on global change research, most of it at agencies
under the jurisdiction of this Committee. I feel strongly
that we need to devote more of that money to research on the
impacts of ozone depletion. We must know more about the
consequences of the damage we are doing to our global
environment.
Today, we will not be using the standard hearing
format. Rather than having panels of witnesses, I have asked
everyone to join in a roundtable discussion. This will
ensure a free and open exchange on the various scientific
questions that researchers are trying to answer and help us
all see clearly where there is general agreement--and where
more work is needed.
I want to welcome our witnesses and thank them for being
here today. Many of them have come a long way and rearranged
very busy schedules to join us and I want to thank you all.
To begin the discussion, I think it would be most useful
if we just went around the table and had everyone briefly
introduce themselves and quickly summarize their research.
Since we have so many people here today, I would ask you to
try to hold your remarks to about three minutes. I guarantee
you that we will have a lot of time to get into the details
later.
2
November 14, 1991
Testimony of Stephen O. Andersen, Senate Committee on Commerce,
Science, and Transportation: Hearing on Global Change Research:
Ozone Depletion and Its Impacts, Friday, November 15, 1991
My name is Stephen 0. Andersen. I am appearing as Co-
Chairman of the United Nations Environment Programme (UNEP
Technical and Economics Assessment. I am not representing the
Environmental Protection Agency. I am Director of Technology
Transfer and Industry Programs in the Global Change Division,
Office of Atmospheric and Indoor Air Programs, Air and Radiation,
of the U.S. Environmental Protection Agency.
The 1991 UNEP Technical and Economic Assessment was
undertaken by over 240 experts from 38 countries.¹ Hundreds of
additional experts served as advisors to the six committees and
as peer reviewers. These include U.S. and foreign industry,
government, and science experts.
The Assessment describes current uses and quantities of
controlled substances, estimates the technically feasible
phaseout dates, estimates the quantity and time period for use of
transitional substitutes, and specifically describes the
implications of a 1997 phaseout. The assessment will not be
final until December but I am pleased to report on the consensus
findings and conclusions as reported in the Executive Summary:
Since 1986 there has been forty percent worldwide drop in
the production of CFCs--this is faster than predicted by the
1989 Assessment and faster than the controls of the Montreal
Protocol.
Several multinational companies are eliminating the use of
ozone-depleting substances far faster than even the most
stringent regulation. By January 1992 the first companies
will have eliminated the use of CFC-113 solvents in all
their worldwide operations; halon and CFC recycling will be
accepted worldwide; the first HFC-134a automobile air
conditioners will be commercialized, and many other ozone-
safe technologies will be available. The first HFC-134a
domestic refrigerators will be commercialized in 1992.
¹Australia, Austria, Bahamas, Belgium, Brazil, Canada,
Chile, China, Denmark, Ecuador, Egypt, France, Germany, India,
Indonesia, Italy, Japan, Jordan, Kenya, Malaysia, Mexico,
Netherlands, New Zealand, Nigeria, Norway, Papua New Guinea,
Singapore, South Korea, Sweden, Switzerland, Trinidad and Tobago,
Tunisia, Uganda, USSR, United Kingdom, United States, Venezuela,
and Yugoslavia.
November 14, 1991
Testimony of Stephen O. Andersen (continued)
Page 2 of 2
The international fire protection community has virtually
eliminated halon emissions caused by discharge testing and
training and service emissions have been drastically
reduced. Educational programs are proving successful as
users move to alternative fire protection measures, where
feasible, and voluntarily limit halon use to essential
applications.
It is technically feasible in developed countries to phase
out production of CFCs and halons by 1997 or earlier, 1,1,1-
trichloroethane as early as 1995, and carbon tetrachloride
in the vast majority of applications by 1995.
These rapid phaseout schedules require that the results of
the toxicity tests, environmental assessments, and risk
analyses conclude that the alternatives HCFC-123, HCFC-124,
HCFC-141b, and HFC-134a can be safely used for
refrigeration, air conditioning, insulating foam, and for
some aerosol, sterilization and minor solvent uses; that
these HCFCs and HFC are environmentally acceptable; and that
they are commercially available in adequate quantities. A
rapid phaseout will also require increased near-term use of
HCFC-22 and HCFC-142b. The halon phaseout is contingent on
the use of recycled halons as the prime supply of those
agents.
There is no perfect substitute. Each substitute has
difficult trade-offs in ODP of transitional substances,
Greenhouse Warming Potential (GWP), energy efficiency, and
toxicity. Trade-offs can be minimized and mitigated by
recycling and bank management, by limiting the use of
transitional or high GWP options to only where necessary,
and by limiting occupational exposures. For small uses,
there are no substitutes yet, but the Technical and Economic
Assessment is optimistic.
It is critical to successful phaseout for developing
countries that technologies are available, that supporting
technical assistance and training is provided, and that
adequate financial assistance is forthcoming. Several
developing countries are entering into innovative technology
cooperation projects. For example, Mexico has announced a
goal of phasing out controlled substances on the same
schedule as developed countries. The Mexican government and
industry are making partnerships with the U.S. Environmental
Protection Agency (EPA), the Industry Cooperative for Ozone
Layer Protection (ICOLP), and Northern Telecom to phase out
solvents. Similar partnerships may speed elimination in
other developing countries.
1
3
EFFECTS OF ULTRAVIOLET-B RADIATION ON IMMUNE RESPONSES
OF MICE AND MEN
Margaret L. Kripke, Ph.D.
Vivian L. Smith Chair in Immunology
Professor and Chairman
Department of Immunology
University of Texas M. D. Anderson Cancer Center
Houston, Texas
United States Senate
Committee on Commerce, Science, and Transportation
Hearing on
Global Change Research: Ozone Depletion and Its Impacts
Friday, November 15, 1991
2
INTRODUCTION
The immune system is the body's primary defense mechanism
against infectious diseases. In addition to providing protection against
bacterial, viral, fungal, and parasitic infections, the immune system
also protects against the development of certain types of cancer,
particularly those associated with cancer viruses and UV radiation (1).
Any impairment of immune function can jeopardize health by increasing
susceptibility to infectious diseases, increasing the severity of
infections, or delaying recovery from infections. In addition, impaired
immune function can increase the incidence of certain cancers,
particularly cancers of the skin (2).
Research carried out with laboratory animals over the past 15
years has demonstrated that exposure of the skin to UV-B radiation can
suppress certain types of immune responses (3). These include
rejection of UV-induced skin cancers (4) and melanomas (5); contact
allergy reactions to chemicals (3); delayed-type hypersensitivity (DTH)
responses to microbial and other antigens (6); and phagocytosis and
elimination of certain bacteria from lymphoid tissues (6).
IMMUNOSUPPRESSIVE EFFECTS OF UVB RADIATION IN ANIMALS
Effects related to skin cancer. The realization that UV-B
radiation can affect the immune system came from studies on the
effects of UV radiation in experimental animals. Many years ago, we
discovered that exposing mice to UV rays caused a systemic change in
their immune system that rendered them incapable of resisting the
development and spread of UV-induced skin cancers (4). We now know
that the systemic change brought about by UVB irradiation involves the
production of suppressor lymphocytes. These white blood cells are part
of the immune system and are responsible for regulating the magnitude
and duration of an immune response. The suppressor lymphocytes
present in mice exposed to repeated doses of UV-B radiation prevent
the development of an immune response against UV-induced skin
cancers. Thus, these suppressor lymphocytes impair the body's natural
defense mechanisms against skin cancer development (7).
Effects on other immune reactions. In trying to determine how
exposing the skin to UV radiation could alter a systemic immune
response, it was discovered that UV-B radiation can suppress other
types of immune reactions, in addition to tumor rejection (3). For
3
example, mice treated with very low (suberythemal) doses of UV-B
radiation fail to make a contact allergy reaction to chemicals applied
through the irradiated skin. Instead, suppressor lymphocytes are
produced. The mechanism involves an alteration in the activity of an
immune cell present in the skin, the epidermal Langerhans cell, which
normally picks up foreign substances in the skin, carries them to the
lymph node, and stimulates the lymphocytes to initiate an immune
reaction. Exposure of Langerhans cells to UV radiation renders them
unable to stimulate the appropriate type of lymphocytes and instead,
suppressor lymphocytes are activated (8).
With higher doses of UV-B, UV-irradiated mice lose their ability
to respond to chemicals applied through unexposed skin (3). They also
have a decreased delayed hypersensitivity response to a variety of
antigens, including those of bacteria, viruses, and fungi (6). The
delayed hypersensitivity response is a lymphocyte-mediated immune
reaction that contributes to the destruction and elimination of various
microorganisms. Suppression of this response by UV irradiation is also
mediated by suppressor lymphocytes. This systemic effect of UV
irradiation has been demonstrated to occur in several species of
animals, to be produced with relevant doses of natural sunlight, to be
due mainly to wavelengths in the UV-B region of the spectrum, and to
increase in proportion to increasing doses of UV radiation (3). The
effect is thought to be due to the release of chemical mediators from
skin cells (keratinocytes) damaged by UV rays.
Effects on infectious diseases. The finding that UV radiation can
suppress certain lymphocyte-mediated immune reactions raised the
possibility that immunity to infectious agents might also be impaired
in UV-irradiated animals. Some disease-causing organisms, such as
Leishmania, Malaria, and Schistosoma, and the leprosy bacillus, gain
entry into the body through the skin. It was therefore possible that the
entry of such organisms through UV-damaged skin might lead to
activation of suppressor lymphocytes instead of a protective immune
response. Other infectious agents, including viruses, bacteria, and
fungi, produce diseases within the skin, and in addition, many
organisms are normally controlled by the delayed hypersensitivity type
of immune response. In these instances, the systemic immune
suppression resulting from UV-B-irradiation could increase the
severity of the disease process and prevent the development of
immunity against reinfection.
4
To date, these possibilities have been tested in only a few animal
models of infectious diseases (Reviewed in 6). The infectious agent
that has been studied most extensively is herpes simplex virus (HSV).
It is well known that UV radiation can trigger active herpes virus
infections in humans and experimental animals that harbor latent virus.
Mice exposed to low doses of UV radiation before inoculation of HSV
showed an increase in the severity of skin lesions and systemic
disease. In addition, low doses of UV radiation suppressed the
induction of delayed hypersensitivity to viral antigens and resulted in
the production of suppressor lymphocytes.
In several murine infectious disease models, mice were given low
doses of UV radiation to impair the function of epidermal Langerhans
cells and then infected with various microorganisms at the site of UV
irradiation. Infection of mice with Leishmania decreased the resultant
delayed hypersensitivity response to this parasite and diminished
immunity to reinfection. However, these low doses of UV radiation had
no effect on the rate of infection with either Leishmania or
Schistosoma parasites, nor did they affect the development of the
delayed hypersensitivity response to a fungus, Candida albicans or a
bacterium Mycobacterium bovis injected subcutaneously at the
irradiated site. The ability of the mice to clear mycobacteria from the
lymphoid tissues was reduced, however, resulting in a prolonged and
more severe infection.
Mice given doses of UV radiation sufficient to cause systemic
immune suppression are unable to make a delayed hypersensitivity
response to candida or mycobacteria injected at a non-irradiated site.
Furthermore, such mice are more susceptible to the lethal effects of an
intravenous inoculation of candida, and their ability to control
mycobacterial infection is greatly reduced, probably because the
macrophages from such animals have reduced phagocytic activity. The
progression of chronic infection of mice with Mycobacterim
lepraemurium is also accelerated in UV-irradiated mice. There is
evidence to suggest that some of these effects of UV irradiation also
result from the action of chemical mediators released from UV-
irradiated keratinocytes.
5
IMMUNOSUPPRESSIVE EFFECTS OF UV RADIATION IN HUMANS
There is increasing evidence that humans are also subject to the
immunosuppressive effects of UV radiation ( Reviewed in 9). For
example, exposing human skin to UV-B radiation damages the -
Langerhans cells and changes the immunologic function of the skin in a
manner similar to that described in mice. Also, several investigators
have documented changes in the proportions of different types of white
blood cells in people exposed to natural and artificial sources of UV
radiation.
Of great interest in this regard are recent studies by Streilein
and colleagues demonstrating that applying a contact allergy-producing
chemical to skin given suberythemal doses of UV radiation fails to
induce the expected immune response in about 40% of normal subjects;
in patients who have had one or more skin cancers, the proportion of
non-responsive individuals approaches 100% (10). This study
demonstrates that humans are subject to at least one of the forms of
immunosuppression identified in mice and suggests, in addition, that
susceptibility to UV-induced immunosuppression constitutes a risk
factor for the development of skin cancer. A second study (11)
compared the same immunosuppressive effect of UV radiation in
different ethnic groups having different amounts of skin pigmentation.
There were no differences in the immunosuppressive effect of UV
radiation in persons with white, brown, or black skin, indicating that
pigmentation is not protective against this form of UV-induced
immunosuppression. Thus, the population at risk of immunological
damage from UV radiation is much larger than that at risk of developing
skin cancer. At present, the significance of this immunological
alteration for infectious diseases in humans is unknown.
CONCLUSIONS
The immunosuppressive effects of UV-B radiation in laboratory
animals are well documented. There is also evidence that UV-induced
immunosuppression can worsen some infectious disease processes in
animal models. Recent studies have shown adverse effects of UV
radiation on immune cells and on some immune functions in humans,
and these effects probably contribute to the induction of skin cancers
in susceptible individuals. However, it is not known whether the
immunological effects of UV radiation can contribute to increases in
6
the incidence or severity of infectious diseases in humans. This is the
most critical unanswered question in attempting to assess the impact
of ozone depletion on human health. Infectious diseases constitute an
enormous public health problem worldwide, and any factor that reduces
immune defenses, thereby increasing the incidence or severity of
infectious diseases, is likely to have a devastating impact on human
health. Studies suggesting that skin pigmentation is not protective
against UV-induced immunosuppression imply that this effect of UV
irradiation is not limited to the Caucasian population at risk of
developing skin cancer, but may extend to other ethnic groups, as well.
Another urgent problem comes from studies in laboratory animals
suggesting that some commercial sunscreen preparations that protect
against sunburn do not protect against the immunosuppressive effects
of UV radiation. If this is true, then the concept that individuals can
protect themselves from the hazardous effects of sunlight exposure by
the use of currently available sunscreens must be reevaluated.
Much more information is also needed on the mechanisms of UV-
induced immunosuppression if we wish to be able to predict the
immunological consequences of increased exposure to UV-B radiation.
7
REFERENCES
1.
Kripke ML. Immunoregulation of Carcinogenesis: Past, Present and
Future (review article). J Natl Cancer Inst, 80:722-727, 1988.
2.
Penn I. Tumors of the immunocompromised patient. Ann Rev Med
39:63-73, 1988.
3.
Kripke ML. Immunological unresponsiveness induced by
ultraviolet radiation. Immunol Rev 80:87-102, 1984.
4.
Kripke ML, Fisher MS. Immunologic parameters of ultraviolet
carcinogenesis. J Natl Cancer Inst 57:211-215, 1976.
5.
Donawho CK, Kripke ML. Evidence that the local effect of UV
radiation on the growth of murine melanomas is immunologically
mediated. Cancer Res 51:4176-4181, 1991.
6.
Jeevan A, Denkins Y, Brown E, Kripke ML. Effects of UV radiation
on infectious diseases. Proceedings of the Symposium on
"Biologic Effects of Light", October 13-15, 1991, Atlanta, GA, in
press.
7.
Fisher MS, Kripke ML. Suppressor T lymphocytes control the
development of primary skin cancers in ultraviolet-irradiated
mice. Science 216:1133-1134, 1982.
8.
Cruz PD Jr, Bergstresser PR. The low-dose model of UVB-induced
immunosuppression (review article). Photodermatol 5:151-161,
1988
9.
Morison WL. Effects of ultraviolet radiation on the immune
system in humans. Photochem Photobiol 50:515-524, 1989.
10. Yoshikawa T, Rae V, Bruins-Slot W, van den Berg J-W, Taylor JR,
Streilein JW. Susceptibility to effects of UVB radiation on
induction of contact hypersensitivity as a risk factor for skin
cancer in man. J Invest Dermatol 95:530-536, 1990.
11. Vermeer M, Schmieder GJ, Yoshikawa T, van den Berg J-W,
Metzman MS, Taylor JR, Streilein JW. Effects of ultraviolet B
light on cutaneous immune responses of humans with deeply
pigmented skin. J Invest Dermatol 97:729-734, 1991.
4
Statement of Ari Patrinos
Director of
The Environmental Sciences Division
Office of Health and Environmental Research
Office of Energy Research
U.S. Department of Energy
before the
United States Senate
Committee on Commerce, Science, and Transportation
November 15, 1991
Mr. Chairman and Members of the Committee:
Stratospheric ozone depletion and its implications for climate change are of
great concern to the Department of Energy (DOE) and I welcome the opportunity
to respond to your invitation to present the Department's views on these
subjects.
The connection between increasing concentrations of greenhouse gases in the
atmosphere and climate change has been investigated by DOE since 1978 when the
term "greenhouse effect" was known only to a few scientists and science
managers. The DOE program, which is integrated into the U.S. Global Change
Research Program coordinated by the Committee on Earth and Environmental
Sciences, has investigated all facets of the issue, from the carbon cycle and
climate diagnostics to the effects on human and natural resources. Since
1988, DOE has quadrupled its annual research investment in this program to $77
million. The focus of our research program is on improving the capability to
predict global and regional climate change. The component of our program most
directly related to stratospheric ozone depletion involves modeling
stratospheric chemical processes and their impact on climate change. DOE also
supports research on the nature of ultraviolet radiation-induced damage to DNA
and the repair of that damage.
DOE is concerned with the mounting evidence of stratospheric ozone depletion
caused by chlorofluorocarbons (CFCs). The Executive Summary of the United
Nations Environment Programme (UNEP) Stratospheric Ozone Assessment released
on October 22, 1991, indicates that the situation is worsening. Strong
Antarctic ozone holes have continued to occur and, for the first time, we have
evidence of stratospheric ozone depletion over mid latitudes and the poles not
2
just during the winter but also during other seasons. Despite some remaining
scientific uncertainties regarding the mechanisms driving ozone depletion, it
is clear that action to curb CFC production and use is both justified and
prudent. This action is in fact an integral part of the Administration's
policy.
DOE would like to focus on statements in the Executive Summary of the UNEP
report that may be perceived to have climate change implications for
stratospheric ozone depletion. The statements appear to be based on
calculations using simplified radiative transfer models and are not
necessarily supported by existing data. Although the report is careful in
describing a possible climate impact in terms of radiative forcing, it is
important to emphasize that any impact on climate change would be highly
uncertain.
Describing "Recent Major Scientific Findings," the UNEP Executive Summary
asserted that, for the decade 1980-1990, middle- and high-latitude ozone
depletion in the lower stratosphere would have canceled the radiative forcing
caused by increases in CFCs at these latitudes. We underscore some of the
uncertainties voiced in the report. First, we believe this conclusion is
based on the application of a one-dimensional radiative transfer model over
various latitudes and seasons using the measured changes in CFCs and ozone
concentrations. Second, we believe that the calculations assumed that the
entire ozone depletion occurred evenly over the bottom seven kilometers of the
stratosphere; in fact roughly 20 percent of the observed ozone change actually
occurred in the upper stratosphere. Third, there is a much stronger seasonal
3
and latitudinal variation in ozone as compared to CFCs and, therefore, the net
effect on climate cannot be estimated by only considering global average
effects. Fourth, the magnitude and even the sign of the change in the
radiative forcing due to decreased lower stratospheric ozone concentrations
are very sensitive to the assumed temperature change in the lower
stratosphere. A decrease in lower stratospheric ozone concentration will
perturb the radiative forcing in the troposphere through a number of distinct
mechanisms involving changes in solar and infrared radiation. The effects can
be separated into direct effects due to ozone changes and indirect effects due
the accompanying cooling of the lower stratosphere. These distinctions may
not adequately be taken into account with simple one-dimensional radiative
transfer calculations such as those used in the UNEP study. Furthermore, any
resulting climate change impacts would require the application of more
comprehensive climate change models.
Simple explanations of complex climate phenomena can sometimes be wrong. For
example, despite the earlier conviction that clouds and polar ice caps would
provide positive feedbacks to a warming climate, recent research has suggested
that the feedbacks may in fact be negative. The results of comprehensive
modeling studies of the ozone-CFC greenhouse effect interaction that are
planned during the next few months by many scientists involved in this
assessment will substantially increase our understanding of these phenomena.
The Executive Summary also reports a number of other results regarding the
greenhouse effect. DOE agrees with the statements in the Executive Summary
regarding uncertainties in Global Warming Potentials (GWPs) for short-lived
4
atmospheric constituents. However, we remain concerned about the
representation of the carbon cycle used in computing the GWPs for all
greenhouse gases. In particular, the current representation of the
atmospheric decay of carbon used in the 1990 Intergovernmental Panel on
Climate Change (IPCC) Assessment, when used with best available historical
data of carbon emissions from fossil fuel burning and land-use change,
overestimates current carbon dioxide concentrations. Thus, it suggests a
relative importance of carbon dioxide that may be larger than its actual
importance in the atmosphere.
For the reasons stated, DOE believes that caution should be exercised before
policy conclusions are drawn. The appropriate forum for assessing the climate
change implications of ozone depletion is the IPCC process. We believe the
IPCC Working Group on science should immediately take up this report with an
eye towards providing a more in-depth assessment of its implications for
climate change.
That concludes my statement. I will be happy to answer your questions.
1
STATEMENT OF
ALAN H. TERAMURA
PROFESSOR AND CHAIRMAN, DEPARTMENT OF BOTANY
UNIVERSITY OF MARYLAND
BEFORE
SENATE COMMITTEE ON COMMERCE, SCIENCE AND TRANSPORTATION
FRIDAY, NOVEMBER 15, 1991
Mr. Chairman, members of the Committee, my name is Alan Teramura. I am a
Professor and Chairman of the Department of Botany at the University of Maryland.
My background is in physiological ecology and I have been conducting studies on the
potential impacts of increases in solar ultraviolet (UV) radiation resulting from
stratospheric ozone depletion on crops and forests for over the past fifteen years. I
have worked closely with a number of U.S. organizations, including the National
Academy of Science, the Environmental Protection Agency and the Department of
Agriculture. Additionally, I have served as a panel member on the biological effects of
ozone depletion for the United Nations Environment Programme and maintain close
collaborations with scientists in the Federal Republic of Germany, Sweden, England,
Japan, and India. I also helped develop a research program coordinated with the
International Rice Research Institute in the Philippines to study the effects of
increasing UV radiation on tropical rice, the world's most important crop plant. I am
appearing before you today to outline the potential consequences of increases in solar
UV radiation on crops, forests, and natural ecosystems.
Over the past 15 years, the scientific community has screened over 300 species
and cultivars of crop plants and alarmingly, over one-half of these seemed to be
2
sensitive to UV radiation. Among the most sensitive plant groups include peas, beans,
squash, melons, and cabbage. For budgetary and logistic reasons, most of this screening
was performed indoors under controlled environment conditions. Without going into
the specific reasons, we now know that plants are generally more sensitive to"UV
radiation under these controlled environments than outdoors. To date, only a dozen
studies have-been performed outdoors in the field on about 20 species of crop plants.
Despite the many problems associated with these field studies, crop yield was reduced
in nearly half of these studies. In a detailed field study conducted at the University of
Maryland, several soybean cultivars were grown during a 6-yr period from 1981-1986.
Increased UV was supplied by artificial sunlamps which simulated up to a 25% ozone
depletion. In a particularly sensitive soybean cultivar, yield was reduced by 20-25% by a
UV level simulating a 25% ozone depletion. In addition to quantitative reductions in
yield, quality can also be adversely affected as seen as reduced protein and oil content
in seed of UV irradiated plants. It is difficult, if not impossible to extrapolate these
results to predict total soybean yields for the U.S. or the world under various ozone
depletion scenarios, since several hundred soybean cultivars are currently grown
worldwide and thousands of new experimental lines are being continually developed.
To date, only about 50 cultivars have been examined for UV sensitivity and
approximately half of these are sensitive based on controlled environment studies. But
this suggests that the other half are somewhat resistant and therefore some degree of
UV resistance already exists in our modern soybean germplasm which may allow
breeders to develop more UV resistant plants in the future. What is presently unknown
is whether these UV resistant cultivars might also carry some unwanted traits such as
increased disease sensitivity, higher water or fertilizer requirement, etc. Preliminary
data also show a similar degree of variation in UV sensitivity for rice, with both very
sensitive and very resistant cultivars identified thus far. Therefore crop breeding may
be one avenue available to us to help mitigate the damaging effects of UV radiation.
3
Although forests represent up to 80% of global terrestrial productivity, very little
is known of the effects of UV on forest tree species. Only 15 tree species from North
America have been screened for UV sensitivity and approximately half of those were
found to be sensitive. Among the most sensitive species include loblolly, red-and
lodgepole pines. Preliminary evidence suggests that long lived plants such as trees can
accumulate the damaging effects of UV radiation over many years. Therefore, even
small, subtle changes which might not be significant during the first few years of growth,
may continue to accumulate throughout the life of the tree. Due to the long lifespan of
trees and the lengthy time required for breeding, forests may be particularly vulnerable
to increases in UV resulting from ozone depletion.
Very little is known of the effects of UV on natural, nonagricultural ecosystems.
To date, fewer than 60 species of native plants have been screened for UV sensitivity.
However, some generalization can be made. Plants which have arisen from naturally
high UV environments such as tropical mountains, are inherently more resistant to UV
radiation, which suggests that these plants have evolved natural adaptations to repair or
protect them from this damage. For example, one recent study of plants collected in
Hawaii concluded that plants growing near sea level were much more sensitive to UV
radiation than plants found growing near mountain tops. Due to this differential
sensitivity, the biodiversity of natural ecosystems may be potentially altered.
Experimental evidence from competition studies in the field indicates that UV
radiation may alter the way in which plants interact and compete with one another
without affecting their overall plant production. This, in turn, could also influence the
biodiversity of natural ecosystems, with the more UV resistant plants replacing those
which are more UV sensitive.
Although only limited information exists, there is evidence to suggest that
exposure to UV radiation also may alter plant sensitivity to diseases, in some cases
making plants much more susceptible to attack by pathogens. Other factors, such as
4
increases in carbon dioxide concentration and temperature which are also of interest
with respect to global climate changes, have been shown to influence and modify the
manner in which plants respond to increased UV radiation. For example, it has been
demonstrated in rice, that the stimulating growth effect of carbon dioxide may not fully
compensate all of the negative UV effects.
Even in the absence of further ozone depletion, the importance of present day
levels of UV radiation has been demonstrated by experimentally reducing current,
natural levels of solar UV radiation reaching plants. In these studies, growth and
photosynthesis of bean seedlings has been altered by present day levels of solar UV.
Whether these results are also true for mature plants has yet to be demonstrated, but
these observations indicate the potential importance of solar UV radiation even
without stratospheric ozone depletion.
Conclusions
1. A large number of crops, native plants, and forest tree species may potentially be
negatively impacted by increases in UV radiation.
- some of these plants are directly sensitive to UV radiation
- others may be indirectly affected by UV-induced increases in plant
competition or disease susceptibility.
2. Due to the existence of genetic adaptations in our modern crops, breeders may be
able to breed more UV-resistant crop plants in the future.
3. However, breeding is not an option for natural plant communities and forests,
where increased UV may result in alterations in biodiversity.
5
4. Other global climate changes such as increased carbon dioxide or global warming
may alter plant responses to UV (sometimes making the situation worse, other
times making it better).
5. Plant research has been limited to only a few ongoing studies where plants are
grown with realistic UV supplements, effectively prohibiting quantitative
assessments or predictions now or in the future.
6. Present day levels of UV radiation can be damaging to plants even in the absence
of ozone depletion.
ENVIRONMENTAL EFFECTS OF OZONE DEPLETION
TESTIMONY OF
JAN C. VAN DER LEUN, Ph.D.
CHAIRMAN, UNEP PANEL ON ENVIRONMENTAL
EFFECTS OF OZONE DEPLETION
BEFORE THE
U.S. SENATE COMMITTEE ON COMMERCE, SCIENCE AND TRANSPORTATION
NOVEMBER 15, 1991
Mr. Chairman, members of the Committee, thank you for the opportunity to give my
contribution to your hearing on ozone depletion and its impacts.
You asked me to give a brief summary of my background. I am Jan C. Van der Leun,
Ph.D., Professor of Dermatology at the University of Utrecht, the Netherlands. My basic training
was in physics. My main research interest became skin photobiology, the study of influences of
light and ultraviolet radiation on human skin. This included the induction of skin cancer by
ultraviolet radiation. Along this way I became involved in assessing the impacts of increased
UV-B radiation to be expected as a consequence of depletion of the ozone layer. Presently I am
chairman of the Panel on Environmental Effects of Ozone Depletion, formed by the United Nations
Environment Programme.
The material I will report to you is based on the work of this Panel. My present testimony
consists largely of the introduction and the executive summary of the Update-1991, just completed
by the Panel. I take the opportunity to highlight a few of the key elements of this Update.
UV-B Radiation
Stratospheric ozone is the dominant factor limiting the penetration of solar UV-B radiation
to the Earth's surface. This radiation is also limited by tropospheric ozone, aerosols and clouds.
Pollution has increased the influence of the latter factors during the past decades. This is probably
the reason some UV-B monitoring series showed a decrease of UV-B radiation while stratospheric
ozone was also decreasing.
Clearcut increases of UV-B radiation were measured in both the Antarctic region during the
presence of the ozone hole and in surrounding areas during the break-up of this hole. Decrease of
UV-B radiation by pollution factors is probably mainly present in industrialized areas; most UV-B
measurements are performed in these areas. There is no guarantee that these factors will continue
to work in the same direction. Efforts to reduce pollution are underway, and in some cases they
are beginning to have success. Climate change may also reduce cloudiness in certain areas. Such
changes may bring out or even amplify the ozone-layer related increases of UV-B radiation; this
would also occur in areas where these changes are masked now.
Human Health
Increase of skin cancer is still the effect for which the best quantitative predictions are
possible. The Update-1991 gives a smaller number for the increase of non-melanoma skin cancer
than the Report-1989. New experimental data show that this type of skin cancer is causedd not
only by UV-B radiation but also, to some extent, by UV-A radiation, which is hardly influenced
by atmospheric ozone. This makes the incidence less sensitive to ozone depletion.
1
Eye problems are expected to be at least as prevalent as discussed in the 1989 report. New
investigations implicate UV-B radiation in more forms of cataract, a leading cause of blindness in
the world.
UV-B radiation has profound influences on the immune system. Recent research confirms
that these occur in man as well as in experimental animals. Skin pigmentation does not protect
against these influences. There is concern that these effects might lead to an increase of infectious
diseases; if this occurs, it will be so for people of all skin colors.
Food Supply
UV-B radiation, even at present levels, has a detrimental effect on many plants and aquatic
organisms. This raises the concern that enhanced UV-B radiation may have a negative influence
on world food production. The relationships between damage to individual organisms and the
productivity of agriculture and fisheries are extremely complex. The scientific data available are by
no means sufficient to make quantitative predictions in these areas.
Biodiversity
If enhanced UV-B radiation has a more negative effect on some species than on others,
then the competitive balance in natural ecosystems may be shifted. There is concern that this may
lead to a loss of species. Again, data are insufficient for precise predictions.
Research
For several potentially important effects, much more knowledge is needed to come to firm
conclusions.
Thank you, Mr. Chairman.
2
UNITED NATIONS
ENVIRONMENT PROGRAMME
ENVIRONMENTAL EFFECTS
OF OZONE DEPLETION:
1991 UPDATE
Introduction
Executive Summary
Panel Report Pursuant to Article 6 of the Montreal Protocol
on substances that Deplete the Ozone layer
under the Auspices of the
United Nations Environment Programme (UNEP)
November 1991
INTRODUCTION
ENVIRONMENTAL EFFECTS
OF OZONE DEPLETION
The Montreal Protocol on Substances that Deplete the Ozone Layer requires in Article
6 periodic assessments of available scientific, environmental, technical and economic information.
The assessments shall be made every four years.
The latest assessments were made in 1989. For the reconsideration of the agreements in
the Montreal Protocol in 1992, UNEP decided that the 1989 assessments would be updated, rather
than making completely new ones. The present report is such an update of the 1989
Environmental Effects Panel Report. It focuses, therefore, on developments since 1989.
Information covered in the previous report that is still up-to-date is not repeated. For this reason,
the chapters of this update include the summary of the corresponding chapter in the 1989 Report.
The occasion calls for an evaluation of how research on effects of increased UV-B
radiation has proceeded during the past years. We cannot conceal that progress is disappointing.
Many of the "Research Needs" formulated in previous reports have to be listed again. The
scientific community has followed some of the recommendations, but by no means all. Urgent
problems are still waiting to be addressed.
The underlying cause has been signalled over many years by the UNEP Co-ordinating
Committee on the Ozone Layer. Funding for research on the consequences of increased UV-B
radiation is disproportionately low, typically less than 1 percent of what is made available for
atmospheric research in relation to ozone depletion. This comment is still valid. There is
improvement of funding in some countries, but this is counterbalanced by a decrease in other
countries. Several research groups, having contributed important information for previous
assessments, have even ceased to exist. Effects research is necessary to provide policy makers
with relevant information, so that they may evaluate response strategies to future challenges. The
possibility to do this in a timely fashion may well depend on the funding situation.
Increased UV-B radiation will have many effects on man, animals, plants, and materials.
For several potentially important effects, our Panel could do no more than express its concern;
more knowledge is needed to come to firm conclusions. The deleterious effects that we
recognize are serious enough to plea for action by the nations of the world to protect the ozone
layer.
J.C. van der Leun
M. Tevini
i
EXECUTIVE SUMMARY
SOLAR INTERACTIONS
Significant global scale decreases in total ozone have occurred over the past ten years.
All other factors being constant, there is no scientific doubt that decreases in total ozone will
increase UV-B radiation at ground level.
Tropospheric ozone and aerosols may have masked the consequences of stratospheric ozone
depletion for UV-B in some industrialized regions.
It is likely that in areas remote from anthropogenic emissions, the UV-B changes due to
stratospheric ozone depletion would be only partially compensated by tropospheric ozone and
aerosol increases.
There are no reliable estimates of the direction or magnitude of effects of any cloud cover
trends on UV-B.
Efforts to improve local and regional air quality may bring to light the increases in UV-B
associated with the depletion of stratospheric ozone.
HEALTH
The induction of immunosuppression by UV-B has now been demonstrated in
humans, not only those of light pigmentation, but also deeply pigmented individuals.
This places all of the world's populations at risk of the potential adverse impacts of UV-B
on the immune system, including possible increases in the incidence or severity of infectious
disease.
An increased number of adverse ocular effects have been associated with exposure to UV.
These include age-related nearsightedness, deformation of the lens capsule, and nuclear
cataract (a form of cataract which previous information excluded from consideration). These
effects appear to be independent of pigmentation. Including nuclear cataract among the
forms of cataract likely to increase with ozone depletion enlarges slightly the risk estimates.
It is now predicted that, all other things being equal, a sustained 10% decrease in ozone will
be associated with between 1.6 and 1.75 million additional cases of cataract per year world-
wide.
Recent information on the relationship of non-melanoma skin cancer to UV exposures
confirms previous findings and has allowed refinement of the carcinogenic action spectrum.
Incorporation of this new information into the risk estimation process has led to slightly
lower predictions. It is now predicted that a sustained 10% decrease in ozone will be
associated with a 26% increase in non-melanoma skin cancer. All other things remaining
ii
constant, this would mean an increase in excess of 300,000 cases per year worldwide.
TERRESTRIAL PLANTS
Continued research on plant responses to UV-B radiation underscores the concern for
agriculture, forestry, and natural ecosystems as the ozone layer is depleted.
Growth and photosynthesis of certain plants (e.g., seedlings of rye, maize, and sunflower)
can be inhibited even under ambient levels of UV-B radiation.
Certain environmental factors, both biotic (e.g., plant diseases and competition with other
plants) and abiotic (e.g., carbon dioxide, temperature, heavy metals, and water availability),
can interact with the effect of UV-B radiation in plants. This makes it difficult to make
quantitative predictions.
Although most research to date has been with plants from temperate regions, data also show
that certain tropical species may be adversely affected by enhanced UV-B radiation.
AQUATIC ECOSYSTEMS
Marine phytoplankton produces at least as much biomass as all terrestrial ecosystems
combined.
Recent results show that the aquatic ecosystem is already under UV-B stress and there is
concern that an increase in UV-B radiation will cause detrimental effects.
One consequence of losses in phytoplankton is reduced biomass production which is
propagated throughout the whole food web. This may result in losses of biomass for human
consumption.
The marine phytoplankton is a major sink for atmospheric carbon dioxide. Any reduction
of the populations would decrease the uptake of carbon dioxide and so augment the
greenhouse effect. Also, phytoplankton production of DMS (dimethylsulphate), which acts
as a precursor of cloud nucleation, would be reduced, hence potentially affecting global
climate.
A UV-B induced decrease in microorganisms fixing atmospheric nitrogen would require
significant substitution by artificial fertilizers, e.g., in rice production.
TROPOSPHERIC AIR QUALITY
Chemical reactivity in the troposphere is expected to increase in response to increases in
UV-B.
Tropospheric ozone concentrations could rise in moderate to heavily polluted areas, but
should decrease in unpolluted regions (with low oxides of nitrogen levels), as recently
iii
confirmed by measurements in the Antarctic.
Other potentially harmful substances (hydrogen peroxide, acids, and aerosols) are expected
to increase in all regions of the troposphere due to the enhanced chemical reactivity.
These changes could exacerbate problems of human health and welfare, increase damage to
the biosphere, and might make current air quality goals more difficult and expensive to
attain.
MATERIALS DAMAGE
UV-B radiation is particularly effective in light-induced degradation of wood and plastic
products, leading to discoloration, and loss of strength. Increased UV-B content in sunlight
will cause more rapid degradation, resulting in increased costs of using higher levels of
conventional light stabilizers, possible design of new stabilizers, and faster replacement of
the affected products.
Available research data are inadequate to reliably estimate the damage from higher UV-B
levels to materials. Very limited relevant data are available for important classes of
materials such as wood, plastic coatings, plastics used outdoors, and rubber. Data pertaining
to performance of plastics in near-equator regions of the world, with the harshest exposure
environments, are particularly needed.
Some on-going work relating to exposure of plastics under desert conditions is likely to
contribute some of the needed data within the next few years. This may lead to improved
assessment of damage to plastics resulting from partial ozone depletion, at that time.
KEY AREAS OF UNCERTAINTY
The key areas of uncertainty are the following:
Quantification of the primary effects on food production and quality, on forestry, and on
natural ecosystems.
Clarification and quantification of influences on human health, especially the immune
system, and occurrences of melanomas and cataracts.
Effects on biota of the enhanced UV radiation during the Antarctic springtime ozone
depletion.
The report on Environmental Effects of Ozone Depletion was prepared by an international group
of scientists. The chairman of the group was Dr. Jan C. van der Leun (The Netherlands), and
the co-chairman was Dr. Manfred Tevini (Federal Republic of Germany).
iv
6a
Executive Summary
Scientific Assessment of Stratospheric Ozone, 1991
22 October 1991
Executive Summary: Scientific Assessment of Stratospheric
Ozone, 1991
22 October 1991
Contents:
Recent Major Scientific Findings
Global ozone decreases
Polar ozone
Ozone and industrial halocarbons
Ozone and climate relations
Ozone Depletion and Global Warming Potentials (ODPs and GWPs)
Supporting Evidence and Related Issues
Global ozone decreases
Polar ozone
Ozone and industrial halocarbons
Ozone and climate relations
Ozone Depletion and Global Warming Potentials (ODPs and GWPs)
Related Issues
Ultraviolet radiation
Supersonic Aircraft
Shuttles and Rockets
Volcanoes, ozone loss, and climate perturbations
Tropospheric sulfate aerosols and climate
Implications For Policy Formulations
Continued global ozone losses
Approaches to lower global risks
Elimination of the Antarctic ozone hole
Uncertain greenhouse role of CFCs
Utility of GWPs
Recent Major Scientific Findings
Over the past few years, there have been highly significant advances in the understanding
of the impact of human activities on the Earth's stratospheric ozone layer and the influence of
changes in chemical composition on the radiative balance of the climate system. Specifically, since
the last international scientific review (1989), there have been five major advances:
Global Ozone Decreases: Ground-based and satellite observations continue to show
decreases of total column ozone in winter in the northern hemisphere. For the first time,
there is evidence of significant decreases in spring and summer in both the northern and
southern hemispheres at middle and high latitudes, as well as in the southern winter. No
trends in ozone have been observed in the tropics. These downward trends were larger
during the 1980s than in the 1970s. The observed ozone decreases have been occurred
predominantly in the lower stratosphere.
Polar Ozone: Strong Antarctic ozone holes have continued to occur and, in four of the
past five years, have been deep and extensive in area. This contrasts to the situation in the
mid-1980s, where the depth and area of the ozone hole exhibited a quasi-biennial
modulation. Large increases in surface ultraviolet radiation have been observed in
Antarctica during periods of low ozone. While no extensive ozone losses have occurred in
the Arctic comparable to those observed in the Antarctic, localized Arctic ozone losses have
been observed in winter concurrent with observations of elevated levels of reactive
chlorine.
Ozone and Industrial Halocarbons: Recent laboratory research and re-interpretation
of field measurements have strengthened the evidence that the Antarctic ozone hole is
primarily due to chlorine- and bromine-containing chemicals. In addition, the weight of
evidence suggests that the observed middle- and high-latitude ozone losses are largely due
to chlorine and bromine. Therefore, as the atmospheric abundances of chlorine and
bromine increase in the future, significant additional losses of ozone are expected at middle
latitudes and in the Arctic.
Ozone and Climate Relations: For the first time, the observed global lower-
stratospheric ozone depletions have been used to calculate the changes in the radiative
balance of the atmosphere. The results indicate that, over the last decade, the observed
ozone depletions would have tended to cool the lower stratosphere at middle and high
latitudes. Temperature data suggest that some cooling indeed has taken place there. The
observed lower-stratospheric ozone changes and calculated temperature changes would
have caused a decrease in the radiative forcing of the surface-troposphere system in the
middle- to high-latitudes that is larger in magnitude than that predicted for the CFC
increases over the last decade. In addition, the ozone depletion may indeed have offset a
significant fraction of the radiative forcing due to increases of all greenhouse gases over the
past decade.
Ozone Depletion and Global Warming Potentials (ODPs and GWPs): A new
semi-empirical, observation-based method of calculating ODPs has better quantified the
role of polar processes in this index. In addition, the direct GWPs for tropospheric, well-
mixed, radiatively active species have been recalculated. However, because of the
incomplete understanding of tropospheric chemical processes, the indirect GWP of
methane has not, at present, been quantified reliably. Furthermore, the concept of a GWP
may prove inapplicable for the very short-lived, inhomogeneously mixed gases, such as the
nitrogen oxides. Hence, many of the indirect GWPs reported in 1990 by the
Intergovernmental Panel on Climate Change (IPCC) are likely to be incorrect.
1
Supporting Evidence and Related Issues
Global Ozone
Independent observations from the ground-based Dobson and M-83/124 instruments
and the TOMS satellite instrument all show, for the first time, that there are significant
decreases in total-column ozone, after accounting for known natural variability, in winter
and now in spring and summer in both the northern and southern hemispheres at middle
and high latitudes, but not in the tropics. The following table illustrates some of these
points.
Total Ozone Trends (% per decade with 95% confidence limits)
TOMS: 1979-91
Ground-based: 26'N - 64°N
Season
45'S
Equator
45°N
1979-1991
1970-1991
Dec-Mar
-5.2 ± 1.5
+0.3 ± 4.5
-5.6 ± 3.5
-4.7 ± 0.9
-2.7 ± 0.7
May-Aug
-6.2 ± 3.0
+0.1 ± 5.2
-2.9 ± 2.1
-3.3 ± 1.2
-1.3 ± 0.4
Sep-Nov
-4.4 ± 3.2
+0.3 + 5.0
-1.7 ± 1.9
-1.2 ± 1.6
-1.2 ± 0.6
There is strong combined observational evidence from balloonsondes, ground-based
Umkehr, and the SAGE satellite instruments that, over the past decade, annual-average
ozone has decreased in the middle- and high-latitude stratosphere below 25 km (about 10%
near 20 km).
Ozone losses in the upper stratosphere have been observed by ground-based Umkehr
and SAGE satellite instruments. Changes in the shape of the vertical distribution of ozone
near 40 km are qualitatively consistent with theoretical predictions, but are smaller in
magnitude.
Measurements indicate that ozone levels in the troposphere up to 10 km above the few
existing balloonsonde stations at northern middle latitudes have increased by about 10% per
decade over the past two decades. However, the data base for ozone trends in the upper
troposphere, where it is an effective greenhouse gas, are sparse and inadequate for
quantifying its contribution to the global radiative balance. It should be noted that the
response of ozone in the upper troposphere is particularly sensitive to oxides of nitrogen
injected by aircraft.
The temperature record indicates that a small cooling (about 0.3°C per decade, globally
averaged) has occurred in the lower stratosphere over the last two decades, which is in the
sense of that expected from the observed ozone change.
Increases continue in the atmospheric abundances of source gases that affect ozone and
the radiative balance. Although methane has continued to increase in the atmosphere, the
rate of increase has slowed, for reasons that are not understood. Methyl bromide is the
major contributor to stratospheric bromine (15 pptv). The sources of methyl bromide are
not well characterized; however, significant anthropogenic emissions have been suggested.
Recent laboratory studies have identified key heterogeneous reactions and have allowed
a more-quantitative assessment of the role of global stratospheric sulfate aerosols in leading
to enhanced abundances of reactive chlorine species.
Limited observations suggest that the abundance of chlorine monoxide (CIO) in the
lower stratosphere at northern middle latitudes is greater than that predicted by models
containing only currently known gas-phase chemistry, and the observed seasonal and
latitudinal dependences are inconsistent with those predicted. Some new studies that
incorporate currently known heterogeneous processes provide an improved simulation for
some observed gases, such as CIO and nitric acid.
Present models containing only gas-phase processes cannot simulate the observed
seasonal ozone depletions at middle and high latitudes. However, models incorporating
currently known heterogeneous processes on sulfate aerosols predict substantially greater
ozone depletion (e.g., a factor of 2 - 3 at middle latitudes) from chlorine and bromine
compounds compared to models containing only gas-phase processes. Indeed, the
heterogeneous models simulate most of the observed trend of column ozone in middle
latitudes in summer, but only about half of that in winter.
There is not a full accounting of the observed downward trends in global ozone.
Plausible mechanisms include (i) local heterogeneous chemistry on stratospheric sulfate
aerosols (as evidenced by, for example, elevated levels of CIO and the presence of sulfate
aerosols at the altitudes of the observed ozone depletion) and (ii) the transport of both
ozone-depleted and chemically perturbed polar air to middle latitudes (as evidenced by high
levels of reactive chlorine and low levels of reactive nitrogen, which is a characteristic of
chemically perturbed polar air). Although other possible mechanisms cannot be ruled out,
those involving chlorine and bromine appear to be largely responsible for the ozone loss
and are the only ones for which direct evidence exists.
Since the middle latitude ozone losses are apparently due in large part to chlorine and
bromine, greater ozone losses are expected as long as the atmospheric levels of these
compounds continue to increase. With the increases in the levels of chlorine and bromine
that are estimated for the year 2000, the additional ozone losses during the 1990s are
expected to be comparable to those already observed for the 1980s.
There are numerous ways in which further increases in stratospheric halogen
abundances can be reduced. The table below illustrates the effects of reducing the
emissions of several types of halocarbons. Four aspects are shown: (i) the change in peak
chlorine loading, (ii) the times at which chlorine abundances have decreased back to 2 ppbv
(the abundance in the late 1970s, which is when the Antarctic ozone hole started and when
the accelerated trends in total-column ozone losses in the northern hemisphere began); (iii)
the times at which chlorine abundances have decreased back to 3 ppbv (the abundance in
the mid-to-late 1980s); and (iv) a measure of the cumulative ozone loss for the time period
that the chlorine levels are above 3 ppbv. All of the values in the table are relative to the
reference scenario (AA).
Scenarios for Reducing Chlorine Emissions
Scenario
Peak CI (ppbv)
Year at 3 ppbv
Year at 2 ppbv
Integral
(Cl>3 ppbv)
AA
4.1 (ppbv)
2027
2060
22.7 ppbv-yr
AA3
-0.18
-10 yrs
-7 yrs
-7.6
D
-0.03
0
0
-1.3
D3
-0.10
0
0
-2.9
E
0.00
-7
-3
-2.0 *
E3
-0.03 *
-10
-3
-4.4 *
F20
+0.01
0
0
+0.8
F40
+0.02
+1
0
+1.5
G20
+0.01
+5
+2
+4.2
AA3 + D3
-0.21
-11
-7
-10.4
*
These values should be reduced by a factor of about 2 - 3 when evaluating ozone loss rather
than chlorine loading.
- Definitions of scenarios:
AA: Montreal Protocol (10 yr lag of 10% of CFCs plus CCI₄; no lag for
CH₃CCI₃ and Halons). HCFC-22 increases at 3% per year from 1991 to 2020,
ramps to 0 by 2040. No substitution of CFCs with HCFCs.
o Non-substitution scenarios:
AA3: 3 year acceleration of CFCs and CCl₄ schedules.
D: 3 year acceleration of CH₃CCl₃ schedule.
D3: CH₃CCl₃ on the accelerated CFC phase-out schedule.
E: HCFC-22 ramp to zero between 2000 and 2020.
E3: HCFC-22 on the accelerated CFC phase-out schedule.
o Substitution scenarios:
HCFC substitutions begin in 1995, no growth to 2000, 3% per year to 2020, ramp to zero by
2030. HCFC-A has a 2 year lifetime, one chlorine, and an ODP of 0.013. HCFC-B has a 20 year
lifetime, one chlorine, and an ODP of 0.13.
F20: 20% initial substitution, HCFC-A.
F40: 40% initial substitution, HCFC-A.
G20: 20% initial substitution, HCFC-B.
is
Stratospheric bromine is 30 - 120 times more efficient than stratospheric chlorine in
destroying ozone on a per atom basis. Therefore, 1 pptv of stratospheric bromine is
equivalent to 0.03 - 0.12 ppbv of stratospheric chlorine.
Polar Ozone
The Antarctic ozone hole in 1991 was as deep and as extensive in area as those of 1987,
1989, and 1990. The low value of total-column ozone measured by TOMS in early
October in 1991 was 110 Dobson units, which is a decrease of about 60% compared to the
ozone levels prior to the late 1970s. The previously noted quasi-biennial modulation of the
severity of the ozone hole did not occur during the past three years. This apparent lack of
variability in recent years may imply that halocarbon chemistry is becoming dominant over
dynamically induced fluctuations of Antarctic ozone depletion.
Recent laboratory studies of heterogeneous processes, reevaluated field measurements,
and modeling studies have strengthened the confidence that the cause of the Antarctic ozone
hole is primarily chlorine and bromine emissions.
High concentrations of CIO have been observed in winter in the Arctic stratosphere
between 16 -20 km. These observations have been incorporated into diagnostic models
that have calculated localized ozone depletions of about 10% at these altitudes over a period
of about a month, which are consistent with concurrent ozone measurements.
Ozone/Climate Relations
The ozone losses observed in the lower stratosphere over the last decade are predicted to
have increased the visible and ultraviolet. incoming solar radiation reaching the
surface/troposphere system and decreased the downward infrared radiation reaching the
surface/troposphere system. For models that allow for the temperature of the stratosphere
to adjust to the loss of ozone, the net effect is a decrease in radiative forcing. For middle
and high latitudes throughout the year, the magnitude of this decrease may be larger than
the predicted increases in the radiative forcing due to the increased abundances of CFCs
over the last decade. Indeed, this ozone-induced decrease in radiative forcing could be
offsetting a significant fraction of the increased forcing attributed to the increases in the
abundances of all greenhouse gases over the same period. Changes in the global annual-
average radiative forcing due to the observed ozone depletion are predicted to be
comparable in magnitude, but opposite in sign, to those attributed to the CFCs over the last
decade.
Current tropospheric models exhibit large differences in their predictions of changes in
ozone, the hydroxyl radical, and other chemically active gases due to emissions of
methane, nonmethane hydrocarbons, carbon monoxide, and nitrogen oxides. This arises
from uncertainties in the knowledge of background chemical composition and an
inadequate understanding of chemical reactions and dynamical processes. Hence, these
deficiencies limit the accuracy of predicted changes in the abundance and distribution of
tropospheric ozone, which is a greenhouse gas, and in the lifetimes of a number of other
greenhouse gases, including the HCFCs and HFCs, which depend upon the abundance of
the hydroxyl radical.
Ozone Depletion and Global Warming Potentials (ODPs and GWPs)
Steady-state and time-dependent ODPs have been recalculated with improved models
that have incorporated more-accurate reaction rate coefficients and absorption cross sections
and known heterogeneous processes on sulfate aerosols. The numerical values are
generally similar to those in previous assessments.
A new semi-empirical, observation-based method of calculating ODPs has been
developed. The resulting values are generally larger (up to a factor of two as compared to
some model-based estimates) for species with long stratospheric lifetimes (e.g., HCFC-22
and HCFC-142b) and slightly smaller for species with short stratospheric lifetimes (e.g.,
carbon tetrachloride and methyl chloroform). Since this approach utilizes more
atmospheric observations and less model calculations in characterizing polar ozone losses,
it is considered to be better than standard model ODPs, at least in the polar regions.
The direct GWPs (with five different time horizons: 20, 50, 100, 200, and 500 years)
for tropospheric, well-mixed, radiatively active species have been recalculated using
updated lifetimes for methane, nitrous oxide, and the halocarbons and following the same
methodology of IPCC (1990). With the exception of methane, new GWP results indicate
only modest changes from the IPCC values, but uncertainties still exist in these calculations
due to limitations in knowledge of the carbon cycle.
Because of incomplete understanding of tropospheric chemical processes, the indirect
GWP of methane has not been quantified reliably at the time of this report, although
improvements and quantifications of uncertainties in the near future are highly likely. The
signs of the net changes in radiative forcing from known indirect effects have been
established for some of the trace gases:-methane, carbon monoxide, and nonmethane
hydrocarbons, which are all positive. The sign of the changes in radiative forcing due to
the nitrogen oxides cannot currently be established. Furthermore, the basic concept of a
GWP may indeed prove to be inapplicable for the very short-lived, inhomogeneously
mixed gases, such as the nitrogen oxides and the nonmethane hydrocarbons. Hence, the
IPCC (1990) indirect GWPs are not only uncertain, but many are also likely to be incorrect
(e.g., for the nitrogen oxides).
Related Issues
Ultraviolet radiation, Significant increases in ultraviolet radiation have been observed
over Antarctica in conjunction with periods of intense ozone depletion. Under clear-sky
conditions, these increases are consistent with theoretical predictions. Furthermore, a
Erythemal Radiative Amplification Factor of 1.25 ± 0.20 has been deduced from
simultaneous measurements of column ozone and surface ultraviolet radiation at a clean air
site, which is in agreement with a model-calculated value of 1.1. Therefore, for the first
time, the response of ground-level ultraviolet radiation to changes in column ozone has
been observed and quantified.
Supersonic aircraft. A previous, independent assessment of the impact of a projected
fleet of supersonic aircraft on stratospheric ozone has reported the prediction that the ozone
loss increases with the amount of nitrogen oxides emitted. These models used gas-phase
chemistry and assessed ozone loss for the case of 500 aircraft flying at Mach 2.4 between
17 - 20 km with an annual fuel use of 7 x 1010 kg/yr. The annual-average loss of column
ozone at middle latitudes in the northern hemisphere is predicted to be 2 6%. For a
comparable fleet operated at Mach between 21 - 24 km, the comparable column ozone
losses are 7 - 12%. However, recent evidence has shown that reactions on sulfate aerosols
can change the partitioning of nitrogen oxides. Two model studies incorporating this
heterogeneous chemistry have recently reexamined the Mach 2.4 case and found
substantially less ozone change (-0.5% to +0.5%). These implications are being examined
as part of a separate assessment.
Shuttles and rockets. The increase in the abundance of stratospheric chlorine from one
projection of U.S. annual launches of nine Space Shuttles and six Titan rockets is
calculated to be less than 0.25% of the annual stratospheric chlorine source from
halocarbons in the present day atmosphere (with maximum increases of 0.01 ppbv in the
middle and upper stratosphere in the northern middle and high latitudes). The TOMS
ozone record shows no detectable changes in column ozone immediately following each of
several launches of the Space Shuttle.
Volcanoes, ozone loss. and climate perturbations. Major volcanic eruptions, such as
Mt. Pinatubo, substantially increase the stratospheric abundance of sulfate aerosols for a
few years. Since laboratory and field data show that heterogeneous processes can lead to
increased levels of reactive chlorine in the stratosphere, such injections have the potential to
increase ozone losses temporarily. Furthermore, the increased levels of stratospheric
sulfate aerosols are predicted to warm the lower stratosphere by about 4°C (which has been
observed) and cool the Earth's surface by a much smaller amount.
Tropospheric sulfate aerosols and climate. Fossil fuel emissions over the past century
have increased the tropospheric sulfate aerosol concentrations. Their contribution to the
direct radiative forcing of the clear-sky northern hemisphere is opposite to that due to the
greenhouse gases and is estimated to be a substantial fraction of the trace gas forcing.
Implications for Policy Formulations
The findings and conclusions of the research of the past few years have several major
implications as input to policy decisions regarding human-influenced substances that lead to
stratospheric ozone depletions and to changes in the radiative forcing of the climate system:
Continued global ozone losses: Even if the control measures of the amended
Montreal Protocol (London, 1990) were to be implemented by all nations, the current abundance of
stratospheric chlorine (3.3 - 3.5 ppbv) is estimated to increase during the next several years,
reaching a peak of about 4.1 ppbv around the turn of the century. With these increases, the
additional middle-latitude ozone losses during the 1990s are expected to be comparable to those
observed during the 1980s, and there is the possibility of incurring wide-spread losses in the
Arctic. Reducing these expected and possible ozone losses requires further limitations on the
emissions of chlorine- and bromine-containing compounds.
Approaches to lowering global risks: Lowering the peak and hastening the
subsequent decline of chlorine and bromine levels can be accomplished in a variety of ways,
including an accelerated phase-out of controlled substances and limitations on currently
uncontrolled halocarbons. Chlorine. A significant reduction in peak chlorine loading (a few tenths
of a ppbv) can be achieved with accelerated phase-out schedules of CFCs, carbon tetrachloride,
and methyl chloroform Even stringent controls on HCFC-22 would not significantly reduce peak
chlorine loading (at most 0.03 ppbv, especially when ODP weighted), but do hasten the decline of
chlorine. Bromine. A 3-year acceleration of the phase-out schedule for the Halons would reduce
peak bromine loading by about 1 pptv. If the anthropogenic sources of methyl bromide are
significant and their emissions can be reduced, then each 10% reduction in methyl bromide would
rapidly result in a decrease in stratospheric bromine of 1.5 pptv, which is equivalent to a reduction
7
in chlorine of 0.045 to 0.18 ppbv. This gain is comparable to that of a three-year acceleration of
the scheduled phase-out of the CFCs.
Elimination of the Antarctic ozone hole: The phase-out schedule of the amended
Montreal Protocol, if fully complied by all nations and if there are no continued uses of HCFCs,
affords the opportunity to return to stratospheric chlorine abundances of 2 ppbv sometime between
the middle and the end of the next century. This is the level at which the Antarctic ozone hole
appeared in the late 1970s and hence is about the level that is thought to be necessary (other
conditions assumed constant, including bromine loading) to eliminate the ozone hole. Such levels
could never have been reached under the provisions of the original Protocol (Montreal, 1987).
Uncertain greenhouse role of CFCs: The weight of evidence suggests that a
large part of the observed lower stratospheric decrease in ozone is the result of CFC emissions.
Furthermore, the radiative impact of this ozone decrease may have largely offset the predicted
direct radiative perturbations, at middle to high latitudes, due to the CFCs increases over the last
decade. Hence, even the sign of the overall radiative effect of CFC increases on the climate system
over the last decade is uncertain.
Utility of GWPs: The direct GWPs are a useful indicator of the relative radiative
effects of long-lived, well-mixed, radiatively active trace species. However, GWPs may be
inapplicable for comparing the direct radiative effects of a long-lived, well-mixed gas to the indirect
effects of a short-lived gas (for example, carbon dioxide to the nitrogen oxides). For the latter
need, the application of new tools, such as three-dimensional, fully coupled coupled chemistry-
climate models may be required.
Statement of
Dr. Robert T. Watson
Earth Science and Applications Division
Office of Space Science and Applications
National Aeronautics and Space Administration
before the
Committee on Commerce, Science, and Transportation
United States Senate
Mr. Chairman and Members of the Committee:
I am pleased to be here to discuss the issue of ozone depletion. The dramatic rise in world
population and industrial activities during the last century have produced the concern that human activities
are affecting the global environment. In particular, there are two inter-related global environment changes,
i.e., atmospheric ozone depletion and global warming, that may effect both human well being and the
quality of life. Ozone depletion is primarily caused through the emissions of anthropogenic chlorine and
bromine containing chemicals into the atmosphere, while global warming is predicted to occur as a result
of increasing atmospheric concentrations of radiatively active trace gases such as carbon dioxide, methane,
nitrous oxide, chlorofluorocarbons and tropospheric ozone. These environmental issues are no longer the
sole concern of the scientific community and environmental groups, and their importance has now been
recognized by governments around the world.
The current concern over ozone depletion has resulted in the endorsement, at the highest levels of
governments, for regular comprehensive scientific, environmental impacts, technical and economic
assessments to be performed. Three state-of-the-art assessments were conducted in response to the
mandate of the Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol on
Substances that Deplete the Ozone Layer. These assessments included: (i) an assessment of our
understanding of the processes controlling the present distribution and rate of change of atmospheric
ozone; (ii) an assessment of the environmental impacts of ozone depletion; and (iii) an assessment of the
technological feasibility and economic costs associated with the substitution of substances controlled under
the Montreal Protocol. The scientific assessment was co-chaired by Dr. Albritton of NOAA and myself;
the impacts assessment was co-chaired by Dr Jan van der Leun of the Netherlands and Dr. Manfred Tevini
of Germany; and the technology/economics assessment was co-chaired by Dr. Stephen Lee-Bapty of the
U.K. and Dr. Stephen Anderson of U.S. EPA.
My testimony today will briefly discuss the key findings of the 1991 International Scientific
Assessment of Ozone Depletion with respect to the extent and cause of ozone depletion and possible
approaches to minimize future ozone depletion. Dr. Daniel Albritton will address the climate implications
of these findings. The executive summary of the scientific assessment is presented verbatim in the
Appendix to this testimony.
Key Findings:
Observational Record: Since the 1989 assessment the observational record includes an
additional 2.5 years of Dobson, SAGE, and TOMS data and a complete re-analysis of 29 ground-
1
based M-83/124 stations in the USSR. This is complemented by a major new advance in the
observational record of an internally calibrated TOMS data set that is now independent of ground-
based observations. Trend analyses of SAGE data have been extended to the lower stratosphere
and the Umkehr data have been reanalyzed.
Antarctic Ozone: The Antarctic ozone hole in 1991 was as deep and as extensive in area as
those of 1987, 1989, and 1990. The low value of total ozone measured in 1991 was 110 Dobson
Units, a decrease of 60% compared to ozone levels prior to the late 1970s. The previously noted
quasi-biennial modulation of the severity of the ozone hole did not occur during the last three
years. The area of the ozone hole was similar for these 4 years.
Trends in Total Ozone: Ground-based (Dobson and M-83/124) and satellite (TOMS)
observations of total column ozone through March 1991 were analyzed allowing for the influence
of solar cycle and quasi-biennial oscillation (see table). They show that:
(a) the northern mid-latitude winter and summer decreases during the 1980s were larger
than the average trend since 1970 by about 2% /decade. A significant longitudinal
variance of the trend since 1979 is observed.
(b) for the first time there are statistically significant decreases in all seasons in both the
northern and southern hemispheres at mid- and high-latitudes during the 1980s; the
northern mid-latitude long-term trends (1970-91), while smaller, are also statistically
significant in all seasons.
(c) there has been no statistically significant decrease in tropical latitudes from 25°N to
25'S.
Total Ozone Trends in %/decade with 95% confidence limits
TOMS: 1979-1991
Ground-based: 26°N - 64°N
45°S
Equator
45°N
1979-1991
1970-1991
Dec-Mar
-5.2 ± 1.5
+0.3 ± 4.5
-5.6 ± 3.5
-4.7 ± 0.9
-2.7 ± 0.7
May-Aug
-6.2 ± 3.0
+0.1 ± 5.2
-2.9 ± 2.1
-3.3 ± 1.2
-1.3 ± 0.4
Sep-Nov
-4.4 ± 3.2
+0.3 ± 5.0
-1.7 ± 1.9
-1.2 ± 1.6
-1.2 ± 0.6
Trends in the Vertical Distribution of Ozone: Balloonsonde, ground-based Umkehr, and
satellite SAGE observations show that:
(a) ozone is decreasing in the lower stratosphere, i.e., below 25 km, at about 10%/decade,
consistent with the observed decrease in column ozone.
(b) changes in the observed vertical distribution of ozone in the upper stratosphere near 40
km are qualitatively consistent with theoretical predictions, but are smaller in
magnitude.
(c) measurements indicate that ozone levels in the troposphere, over the few existing ozone
sounding stations at northern mid-latitudes, have increased about 10%/decade over the
past 2 decades.
2
Ultraviolet radiation: Significant increases in ultraviolet radiation have been observed over Antarctica
in conjunction with periods of intense ozone depletion. Under clear-sky conditions, these increases are
consistent with theoretical predictions. Therefore, for the first time, the response of ground-level
ultraviolet radiation to changes in column ozone has been observed and quantified.
Cause of the Observed Ozone Depletion: Recent laboratory research and re-interpretation of field
measurements have strengthened the evidence that the Antarctic ozone hole is primarily due to chlorine-
and bromine-containing chemicals. In addition, the weight of evidence suggests that the observed middle-
and high-latitude ozone losses are largely due to chlorine and bromine.
Future Levels of Ozone Depletion: Even if the control measures of the amended Montreal Protocol
(London, 1990) were to be implemented by all nations, the current abundance of stratospheric chlorine
(3.3 - 3.5 parts per billion volume (ppbv)) is estimated to increase during the next several years, reaching a
peak of about 4.1 ppbv around the turn of the century. Since the middle latitude ozone losses are
apparently due in large part to chlorine and bromine, the increased levels of chlorine and bromine that are
estimated by the year 2000 are expected to result in additional ozone losses during the 1990s comparable to
those already observed for the 1980s. There is also the possibility of incurring wide-spread losses in the
Arctic. Reducing these expected and possible ozone losses requires further limitations on the emissions of
chlorine- and bromine-containing compounds.
Approaches to Limiting Future Levels of Ozone Depletion: Lowering the peak chlorine
loading by a few tenths of a ppbv and the peak bromine loading by about 1 parts per trillion by volume
(pptv), and hastening the subsequent decline of chlorine and bromine levels can be accomplished in a
variety of ways, including accelerating all regulatory steps on controlled substances (CFCs, carbon
tetrachloride, methyl chloroform, and Halons) by about 3 years and limitations on currently uncontrolled
halocarbons (e.g., HCFC-22). It should also be noted that if the anthropogenic sources of methyl
bromide are significant and their emissions can be reduced, then each 10% reduction in methyl bromide
would rapidly result in a decrease in stratospheric bromine of 1.5 pptv, which is equivalent to a reduction
in stratospheric chlorine of 0.045 to 0.18 ppbv. This gain is comparable to that of a three-year acceleration
of the scheduled phase-out of the CFCs.
3
APPENDIX
Executive Summary of the Scientific Assessment of Ozone Depletion
Recent Major Scientific Findings
Over the past few years, there have been highly significant advances in the understanding
of the impact of human activities on the Earth's stratospheric ozone layer and the influence of
changes in chemical composition on the radiative balance of the climate system. Specifically, since
the last international scientific review (1989), there have been five major advances:
Global Ozone Decreases: Ground-based and satellite observations continue to show
decreases of total column ozone in winter in the northern hemisphere. For the first time,
there is evidence of significant decreases in spring and summer in both the northern and
southern hemispheres at middle and high latitudes, as well as in the southern winter. No
trends in ozone have been observed in the tropics. These downward trends were larger
during the 1980s than in the 1970s. The observed ozone decreases have occurred
predominantly in the lower stratosphere.
Polar Ozone: Strong Antarctic ozone holes have continued to occur and, in four of the
past five years, have been deep and extensive in area. This contrasts to the situation in the
mid-1980s, where the depth and area of the ozone hole exhibited a quasi-biennial
modulation. Large increases in surface ultraviolet radiation have been observed in
Antarctica during periods of low ozone. While no extensive ozone losses have occurred in
the Arctic comparable to those observed in the Antarctic, localized Arctic ozone losses have
been observed in winter concurrent with observations of elevated levels of reactive
chlorine.
Ozone and Industrial Halocarbons: Recent laboratory research and re-interpretation
of field measurements have strengthened the evidence that the Antarctic ozone hole is
primarily due to chlorine- and bromine-containing chemicals. In addition, the weight of
evidence suggests that the observed middle- and high-latitude ozone losses are largely due
to chlorine and bromine. Therefore, as the atmospheric abundances of chlorine and
bromine increase in the future, significant additional losses of ozone are expected at middle
latitudes and in the Arctic.
Ozone and Climate Relations: For the first time, the observed global lower-
stratospheric ozone depletions have been used to calculate the changes in the radiative
balance of the atmosphere. The results indicate that, over the last decade, the observed
ozone depletions would have tended to cool the lower stratosphere at middle and high
latitudes. Temperature data suggest that some cooling indeed has taken place there. The
observed lower-stratospheric ozone changes and calculated temperature changes would
have caused a decrease in the radiative forcing of the surface-troposphere system in the
middle- to high-latitudes that is larger in magnitude than that predicted for the CFC
increases over the last decade. In addition, the ozone depletion may indeed have offset a
significant fraction of the radiative forcing due to increases of all greenhouse gases over the
past decade.
Ozone Depletion and Global Warming Potentials (ODPs and GWPs): A new
semi-empirical, observation-based method of calculating ODPs has better quantified the
role of polar processes in this index. In addition, the direct GWPs for tropospheric, well-
mixed, radiatively active species have been recalculated. However, because of the
4
incomplete understanding of tropospheric chemical processes, the indirect GWP of
methane has not, at present, been quantified reliably. Furthermore, the concept of a GWP
may prove inapplicable for the very short-lived, inhomogeneously mixed gases, such as the
nitrogen oxides. Hence, many of the indirect GWPs reported in 1990 by the
Intergovernmental Panel on Climate Change (IPCC) are likely to be incorrect.
Supporting Evidence and Related Issues
Global Ozone
Independent observations from the ground-based Dobson and M-83/124 instruments
and the TOMS satellite instrument all show, for the first time, that there are significant
decreases in total-column ozone, after accounting for known natural variability, in winter
and now in spring and summer in both the northern and southern hemispheres at middle
and high latitudes, but not in the tropics. The following table illustrates some of these
points.
Total Ozone Trends (% per decade with 95% confidence limits)
TOMS: 1979-91
Ground-based: 26°N - 64°N
Season
45°S
Equator
45°N
1979-1991
1970-1991
Dec-Mar
-5.2 ± 1.5
+0.3 ± 4.5
-5.6 ± 3.5
-4.7 ± 0.9
-2.7 ± 0.7
May-Aug
-6.2 ± 3.0
+0.1 ± 5.2
-2.9 ± 2.1
-3.3 ± 1.2
-1.3 ± 0.4
Sep-Nov
-4.4 ± 3.2
+0.3 ± 5.0
-1.7 ± 1.9
-1.2 ± 1.6
-1.2 ± 0.6
There is strong combined observational evidence from balloonsondes, ground-based
Umkehr, and the SAGE satellite instruments that, over the past decade, annual-average
ozone has decreased in the middle- and high-latitude stratosphere below 25 km (about 10%
near 20 km).
Ozone losses in the upper stratosphere have been observed by ground-based Umkehr
and SAGE satellite instruments. Changes in the shape of the vertical distribution of ozone
near 40 km are qualitatively consistent with theoretical predictions, but are smaller in
magnitude.
Measurements indicate that ozone levels in the troposphere up to 10 km above the few
existing balloonsonde stations at northern middle latitudes have increased by about 10% per
decade over the past two decades. However, the data base for ozone trends in the upper
troposphere, where it is an effective greenhouse gas, are sparse and inadequate for
quantifying its contribution to the global radiative balance. It should be noted that the
response of ozone in the upper troposphere is particularly sensitive to oxides of nitrogen
injected by aircraft.
The temperature record indicates that a small cooling (about 0.3°C per decade, globally
averaged) has occurred in the lower stratosphere over the last two decades, which is in the
sense of that expected from the observed ozone change.
Increases continue in the atmospheric abundances of source gases that affect ozone and
the radiative balance. Although methane has continued to increase in the atmosphere, the
rate of increase has slowed, for reasons that are not understood. Methyl bromide is the
major contributor to stratospheric bromine (15 pptv). The sources of methyl bromide are
not well characterized; however, significant anthropogenic emissions have been suggested.
5
Recent laboratory studies have identified key heterogeneous reactions and have allowed
a more-quantitative assessment of the role of global stratospheric sulfate aerosols in leading
to enhanced abundances of reactive chlorine species.
Limited observations suggest that the abundance of chlorine monoxide (CIO) in the
lower stratosphere at northern middle latitudes is greater than that predicted by models
containing only currently known gas-phase chemistry, and the observed seasonal and
latitudinal dependences are inconsistent with those predicted. Some new studies that
incorporate currently known heterogeneous processes provide an improved simulation for
some observed gases, such as CIO and nitric acid.
Present models containing only gas-phase processes cannot simulate the observed
seasonal ozone depletions at middle and high latitudes. However, models incorporating
currently known heterogeneous processes on sulfate aerosols predict substantially greater
ozone depletion (e.g., a factor of 2 - 3 at middle latitudes) from chlorine and bromine
compounds compared to models containing only gas-phase processes. Indeed, the
heterogeneous models simulate most of the observed trend of column ozone in middle
latitudes in summer, but only about half of that in winter.
There is not a full accounting of the observed downward trends in global ozone.
Plausible mechanisms include (i) local heterogeneous chemistry on stratospheric sulfate
aerosols (as evidenced by, for example, elevated levels of CIO and the presence of sulfate
aerosols at the altitudes of the observed ozone depletion) and (ii) the transport of both
ozone-depleted and chemically perturbed polar air to middle latitudes (as evidenced by high
levels of reactive chlorine and low levels of reactive nitrogen, which is a characteristic of
chemically perturbed polar air). Although other possible mechanisms cannot be ruled out,
those involving chlorine and bromine appear to be largely responsible for the ozone loss
and are the only ones for which direct evidence exists.
Since the middle latitude ozone losses are apparently due in large part to chlorine and
bromine, greater ozone losses are expected as long as the atmospheric levels of these
compounds continue to increase. With the increases in the levels of chlorine and bromine
that are estimated for the year 2000, the additional ozone losses during the 1990s are
expected to be comparable to those already observed for the 1980s.
There are numerous ways in which further increases in stratospheric halogen
abundances can be reduced. The table below illustrates the effects of reducing the
emissions of several types of halocarbons. Four aspects are shown: (i) the change in peak
chlorine loading, (ii) the times at which chlorine abundances have decreased back to 2 ppbv
(the abundance in the late 1970s, which is when the Antarctic ozone hole started and when
the accelerated trends in total-column ozone losses in the northern hemisphere began); (iii)
the times at which chlorine abundances have decreased back to 3 ppbv (the abundance in
the mid-late 1980s); and (iv) a measure of the cumulative ozone loss for the time period that
the chlorine levels are above 3 ppbv. All of the values in the table are relative to the
reference scenario (AA).
6
Scenarios for Reducing Chlorine Emissions
Scenario
Peak CI (ppbv)
Year at 3 ppbv
Year at 2 ppbv
Integral
(Cl>3 ppbv)
AA
4.1 (ppbv)
2027
2060
22.7 ppbv-yr
AA3
-0.18
-10 yrs
-7 yrs
-7.6
D
-0.03
0
0
-1.3
D3
-0.10
0
0
-2.9
E
0.00
-7
-3
-2.0 *
E3
-0.03 *
-10
-3
-4.4 *
F20
+0.01
0
0
+0.8
F40
+0.02
+1
0
+1.5
G20
+0.01
+5
+2
+4.2
AA3 + D3
-0.21
-11
-7
-10.4
*
These values should be reduced by a factor of about 2 - 3 when evaluating ozone loss rather
than chlorine loading.
Definitions of scenarios:
AA: Montreal Protocol (10 yr lag of 10% of CFCs plus CCI₄; no lag for
CH₃CCl₃ and Halons). HCFC-22 increases at 3% per year from 1991 to 2020,
ramps to 0 by 2040. No substitution of CFCs with HCFCs.
o Non-substitution scenarios:
AA3: 3 year acceleration of CFCs and CCl4 schedules.
D: 3 year acceleration of CH₃CCl₃ schedule.
D3: CH₃CCl₃ on the accelerated CFC phase-out schedule.
E: HCFC-22 ramp to zero between 2000 and 2020.
E3: HCFC-22 on the accelerated CFC phase-out schedule.
o Substitution scenarios:
HCFC substitutions begin in 1995, no growth to 2000, 3% per year to 2020, ramp to zero by
2030. HCFC-A has a 2 year lifetime, one chlorine, and an ODP of 0.013. HCFC-B has a 20 year
lifetime, one chlorine, and an ODP of 0.13.
F20: 20% initial substitution, HCFC-A.
F40: 40% initial substitution, HCFC-A.
G20: 20% initial substitution, HCFC-B.
Stratospheric bromine is 30 - 120 times more efficient than stratospheric chlorine in
destroying ozone on a per atom basis. Therefore, 1 pptv of stratospheric bromine is
equivalent to 0.03 - 0.12 ppbv of stratospheric chlorine.
Polar Ozone
The Antarctic ozone hole in 1991 was as deep and as extensive in area as those of 1987,
1989, and 1990. The low value of total-column ozone measured by TOMS in early
October in 1991 was 110 Dobson units, which is a decrease of about 60% compared to the
ozone levels prior to the late 1970s. The previously noted quasi-biennial modulation of the
severity of the ozone hole did not occur during the past three years. This apparent lack of
7
variability in recent years may imply that halogen chemistry is becoming dominant over
dynamically induced fluctuations on Antarctic ozone depletion.
Recent laboratory studies of heterogeneous processes, reevaluated field measurements,
and modeling studies have strengthened the confidence that the cause of the Antarctic ozone
hole is primarily chlorine and bromine emissions.
High concentrations of CIO have been observed in winter in the Arctic stratosphere
between 16 -20 km. These observations have been incorporated into diagnostic models
that have calculated localized ozone depletions of about 10% at these altitudes over a period
of about a month, which are consistent with concurrent ozone measurements.
Ozone/Climate Relations
The ozone losses observed in the lower stratosphere over the last decade are predicted to
have increased the visible and ultraviolet incoming solar radiation reaching the
surface/troposphere system and decreased the downward infrared radiation reaching the
surface/troposphere system. For models that allow for the temperature of the stratosphere
to adjust to the loss of ozone, the net effect is a decrease in radiative forcing. For middle
and high latitudes throughout the year, the magnitude of this decrease may be larger than
the predicted increases in the radiative forcing due to the increased abundances of CFCs
over the last decade. Indeed, this ozone-induced decrease in radiative forcing could be
offsetting a significant fraction of the increased forcing attributed to the increases in the
abundances of all greenhouse gases over the same period. Changes in the global annual-
average radiative forcing due to the observed ozone depletion are predicted to be
comparable in magnitude, but opposite in sign, to those attributed to the CFCs over the last
decade.
Current tropospheric models exhibit large differences in their predictions of changes in
ozone, the hydroxyl radical, and other chemically active gases due to emissions of
methane, nonmethane hydrocarbons, carbon monoxide, and nitrogen oxides. This arises
from uncertainties in the knowledge of background chemical composition and an
inadequate understanding of chemical reactions and dynamical processes. Hence, these
deficiencies limit the accuracy of predicted changes in the abundance and distribution of
tropospheric ozone, which is a greenhouse gas, and in the lifetimes of a number of other
greenhouse gases, including the HCFCs and HFCs, which depend upon the abundance of
the hydroxyl radical.
Ozone Depletion and Global Warming Potentials (ODPs and GWPs)
Steady-state and time-dependent ODPs have been recalculated with improved models
that have incorporated more-accurate reaction rate coefficients and absorption cross sections
and known heterogeneous processes on sulfate aerosols. The numerical values are
generally similar to those in previous assessments.
A new semi-empirical, observation-based method of calculating ODPs has been
developed. The resulting values are generally larger (up to a factor of two as compared to
some model-based estimates) for species with long stratospheric lifetimes (e.g., HCFC-22
and HCFC-142b) and slightly smaller for species with short stratospheric lifetimes (e.g.,
carbon tetrachloride and methyl chloroform). Since this approach utilizes more
atmospheric observations and less model calculations in characterizing polar ozone losses,
it is considered to be better than standard model ODPs, at least in the polar regions.
The direct GWPs (with five different time horizons: 20, 50, 100, 200, and 500 years)
for tropospheric, well-mixed, radiatively active species have been recalculated using
updated lifetimes for methane, nitrous oxide, and the halocarbons and following the same
methodology of IPCC (1990). With the exception of methane, new GWP results indicate
8
only modest changes from the IPCC values, but uncertainties still exist in these calculations
due to limitations in knowledge of the carbon cycle.
Because of incomplete understanding of tropospheric chemical processes, the indirect
GWP of methane has not been quantified reliably at the time of this report, although
improvements and quantifications of uncertainties in the near future are highly likely. The
signs of the net changes in radiative forcing from known indirect effects have been
established for some of the trace gases: methane, carbon monoxide, and nonmethane
hydrocarbons, which are all positive. The sign of the changes in radiative forcing due to
the nitrogen oxides cannot currently be established. Furthermore, the basic concept of a
GWP may indeed prove to be inapplicable for the very short-lived, inhomogeneously
mixed gases, such as the nitrogen oxides and the nonmethane hydrocarbons. Hence, the
IPCC (1990) indirect GWPs are not only uncertain, but many are also likely to be incorrect
(e.g., for the nitrogen oxides).
Related Issues
Ultraviolet radiation. Significant increases in ultraviolet radiation have been observed
over Antarctica in conjunction with periods of intense ozone depletion. Under clear-sky
conditions, these increases are consistent with theoretical predictions. Furthermore, a
Erythemal Radiative Amplification Factor of 1.25 ± 0.20 has been deduced from
simultaneous measurements of column ozone and surface ultraviolet radiation at a clean air
site, which is in agreement with a model-calculated value of 1.1. Therefore, for the first
time, the response of ground-level ultraviolet radiation to changes in column ozone has
been observed and quantified.
Supersonic aircraft. A previous, independent assessment of the impact of a projected
fleet of supersonic aircraft on stratospheric ozone has reported the prediction that the ozone
loss increases with the amount of nitrogen oxides emitted. These models used gas-phase
chemistry and assessed ozone loss for the case of 500 aircraft flying at Mach 2.4 between
17 - 20 km with an annual fuel use of 7 X 1010 kg/yr. The annual-average loss of column
ozone at middle latitudes in the northern hemisphere is predicted to be 2 - 6%. For a
comparable fleet operated at Mach 3.2 between 21 - 24 km, the comparable column ozone
losses are 7 - 12%. However, recent evidence has shown that reactions on sulfate aerosols
can change the partitioning of nitrogen oxides. Two mode! studies incorporating this
heterogeneous chemistry have recently reexamined the Mach 2.4 case and found
substantially less ozone change (-0.5% to +0.5%). These implications are being examined
as part of a separate assessment.
Shuttles and rockets. The increase in the abundance of stratospheric chlorine from one
projection of U.S. annual launches of nine Space Shuttles and six Titan rockets is
calculated to be less than 0.25% of the annual stratospheric chlorine source from
halocarbons in the present day atmosphere (with maximum increases of 0.01 ppbv in the
middle and upper stratosphere in the northern middle and high latitudes). The TOMS
ozone record shows no detectable changes in column ozone immediately following each of
several launches of the Space Shuttle.
Volcanoes, ozone loss, and climate perturbations, Major volcanic eruptions, such as
Mt. Pinatubo, substantially increase the stratospheric abundance of sulfate aerosols for a
few years. Since laboratory and field data show that heterogeneous processes can lead to
increased levels of reactive chlorine in the stratosphere, such injections have the potential to
increase ozone losses temporarily. Furthermore, the increased levels of stratospheric
sulfate aerosols are predicted to warm the lower stratosphere by about 4°C (which has been
observed) and cool the Earth's surface by a much smaller amount.
Tropospheric sulfate aerosols and climate. Fossil fuel emissions over the past century
have increased the tropospheric sulfate aerosol concentrations. Their contribution to the
9
direct radiative forcing of the clear-sky northem hemisphere is opposite to that due to the
greenhouse gases and is estimated to be a substantial fraction of the trace gas forcing.
Implications for Policy Formulations
The findings and conclusions of the research of the past few years have several major
implications as input to policy decisions regarding human-influenced substances that lead to
stratospheric ozone depletions and to changes in the radiative forcing of the climate system:
Continued global ozone losses: Even if the control measures of the amended
Montreal Protocol (London, 1990) were to be implemented by all nations, the current abundance of
stratospheric chlorine (3.3 - 3.5 ppbv) is estimated to increase during the next several years,
reaching a peak of about 4.1 ppbv around the turn of the century. With these increases, the
additional middle-latitude ozone losses during the 1990s are expected to be comparable to those
observed during the 1980s, and there is the possibility of incurring wide-spread losses in the
Arctic. Reducing these expected and possible ozone losses requires further limitations on the
emissions of chlorine- and bromine-containing compounds.
Approaches to lowering global risks: Lowering the peak and hastening the
subsequent decline of chlorine and bromine levels can be accomplished in a variety of ways,
including an accelerated phase-out of controlled substances and limitations on currently
uncontrolled halocarbons. Chlorine, A significant reduction in peak chlorine loading (a few tenths
of a ppbv) can be achieved with accelerated phase-out schedules of CFCs, carbon tetrachloride,
and methyl chloroform Even stringent controls on HCFC-22 would not significantly reduce peak
chlorine loading (at most 0.03 ppbv, especially when ODP weighted), but do hasten the decline of
chlorine. Bromine. A 3-year acceleration of the phase-out schedule for the Halons would reduce
peak bromine loading by about 1 pptv. If the anthropogenic sources of methyl bromide are
significant and their emissions can be reduced, then each 10% reduction in methyl bromide would
rapidly result in a decrease in stratospheric bromine of 1.5 pptv, which is equivalent to a reduction
in stratospheric chlorine of 0.045 to 0.18 ppbv. This gain is comparable to that of a three-year
acceleration of the scheduled phase-out of the CFCs.
Elimination of the Antarctic ozone hole: The phase-out schedule of the amended
Montreal Protocol, if fully complied by all nations and if there are no continued uses of HCFCs,
affords the opportunity to return to stratospheric chlorine abundances of 2 ppbv sometime between
the middle and the end of the next century. This is the level at which the Antarctic ozone hole
appeared in the late 1970s and hence is about the level that is thought to be necessary (other
conditions assumed constant, including bromine loading) to eliminate the ozone hole. Such levels
could never have been reached under the provisions of the original Protocol (Montreal, 1987).
Uncertain greenhouse role of CFCs: The weight of evidence suggests that a
large part of the observed lower stratospheric decrease in ozone is the result of CFC emissions.
Furthermore, the radiative impact of this ozone decrease may have largely offset the predicted
direct radiative perturbations, at middle to high latitudes, due to the CFCs increases over the last
decade. Hence, even the sign of the overall radiative effect of CFC increases on the climate system
over the last decade is uncertain.
Utility of GWPs: The direct GWPs are a useful indicator of the relative radiative
effects of long-lived, well-mixed, radiatively active trace species. However, GWPs may be
inapplicable for comparing the direct radiative effects of a long-lived, well-mixed gas to the indirect
effects of a short-lived gas (for example, carbon dioxide to the nitrogen oxides). For the latter
need, the application of new tools, such as three-dimensional, fully coupled coupled chemistry-
climate models may be required.
10
Senate Commerce, Science and Transportation Committee
Hearing on
Global Change Research: Ozone Depletion and Its Impacts
November 15, 1991
Russell Bldg. Room 253 9:30 a.m.
Subject: Effects of Ozone-Related Increases in UV-B Radiation on Marine
Phytoplankton
Testimony by: C. Susan Weiler, Ph.D.
Executive Director, American Society of Limnology and Oceanography
Department of Biology, Whitman College, Walla Walla, WA 99362
Witness' Background: I am presently the Executive Director for the American Society of
Limnology and Oceanography, an organization of professional aquatic scientists which has
disseminated scientific information and furthered understanding of aquatic systems since 1936. I
have a B.A. in Biology from the University of California at San Diego (1972) and a Ph.D. in
Oceanography from the Scripps Institution of Oceanography (1978). My research over the past 17
years has focused on the physiological ecology of marine phytoplankton. I served as a program
officer for the National Science Foundation's Polar Biology and Medicine Program during 1987-
88. At that time, decisions were made to establish a network of instruments for continuous
monitoring UV radiation at all four U.S. Antarctic bases and in South America, and to establish a
special program to study the biological consequences of stratospheric ozone depletion. I
supervised the development of the UV monitoring equipment and network, and served as the
program director for the special program on biological research related to ozone depletion. I have
not conducted UV-B related research directly, but have remained actively involved in the UV-B
research community through work as a scientific administrator, editor, meeting organizer, and
workshop participant. Today I will summarize the status of UV-B research on marine
phytoplankton.
INTRODUCTION
Phytoplankton are the tiny, generally free-floating and single-cell plants that form the base of the
oceanic food chain. these organisms can generally grow as deep as the 1% or 0.01% light level,
which reaches approximately 150 m on a sunny day in clear water. It has been known for a long
time that ultraviolet radiation can penetrate to ecologically significant depths. Because of this UV-
B radiation penetration, phytoplankton and other aquatic organisms are at risk from the depletion of
ozone in the upper atmosphere. The depth of penetration varies with water clarity, the amount and
composition of UV-B absorbing compounds, atmospheric turbidity and clouds, and with the
wavelength of the UV-B radiation. Ecologically significant penetration may be more than 30 m on
a sunny day in clear water. While some information exists on UV-B effects on phytoplankton, the
full consequences of stratospheric ozone depletion on marine phytoplankton and ecosystems
cannot yet be assessed.
UV-B affects many different processes in phytoplankton, including cell viability, DNA integrity,
photosynthesis, nutrient uptake, pigmentation, motility and orientation, protein content, and cell
division, and there may be positive or negative synergistic responses. At present we know little
about UV-B effects on the individual systems, let alone the combined effects. These are difficult to
address, particularly because effects may express themselves over different time scales.
UV-B effects on cell constituents vary tremendously with wavelength as well as intensity. The
shorter the wavelength, the greater the energy and subsequent effect. Thus, it is imperative to have
wavelength-specific radiation measurements when studying UV-B effects. Because absorption
varies as a function of wavelength as well as depth, UV-B should be measured at each
experimental depth. And because phytoplankton cells are subject to constant vertical mixing,
experiments at fixed depths can only approximate the effect on organisms experiencing natural
water movement.
Visible (400 - 700 nm) and UV-A (320-400 nm) radiation and UV-B (280-320 nm) radiation are
all important in the context of how organisms respond to ozone-related increases in UV-B
radiation. Visible radiation is necessary for photosynthesis, which provides energy for
photoprotection, photorepair and other physiological processes. While UV-A radiation is -
damaging, it also plays a role in photorepair processes. Because UV-A and visible radiation are
not absorbed by ozone and UV-B is, the ratio of UV-B/(UV-A + Visible + UV-B) increases with
decreasing ozone. Such changes in the ratio of wavelengths could alter at least some species
consideration. responses. The importance of changes in this ratio for cell processes is currently under
While we do know that it is important to conduct experiments using naturally occurring spectra and
ratios, research has been limited because artificial lights do not mimic the natural radiation
spectrum. The recent ozone depletion over the Antarctic and the related increases in UV-B
radiation have freed researchers from the constraints imposed by artificial lights. UV-B changes in
the Antarctic are both large and rapid because the size, shape and position of the ozone hole varies
with time. Phytoplankton and other organisms may therefore be subject over a few days to
increases in UV-B comparable to past seasonal changes.
EFFECTS OF UV-B ON MARINE PHYTOPLANKTON
Effects of UV-B on marine phytoplankton include:
Damage to DNA and other important cellular molecules and processes
Absorption of UV-B can cause irreparable damage to the genetic material or disrupt other metabolic
processes, and can eventually result in death. Protein content, dry weight, and pigment
concentration have all been found to decrease after UV-B exposure. Recent work in the Antarctic
using a non-marine bacterial dosimeter found that DNA damage was directly related to atmospheric
ozone concentrations; effects were found as deep as 37 m. Because a UV-B sensitive bacterial
strain is needed for the dosimeter, results represent the extreme case. Researchers have
demonstrated that, despite the low-light conditions characteristic of the Antarctic, phytoplankton
species are similar to temperate species in their ability to produce UV-blocking compounds and
repair DNA damage caused by UV radiation. However, species are variable in their capacity to
resist UV-B related damage. In one study, the species varied in sensitivity by a factor of 100.
More research is needed to assess species differences in protective mechanisms and to assess the
response of species to different radiation conditions.
Reduction of phytoplankton production.
Photosynthesis has been shown to be inhibited by UV-B radiation.
Incident UV-B doses in the Antarctic have more than doubled over pre-ozone hole values, and
organisms at some locations are now getting a dose of UV-B higher even than what they would
normally experience even at the summer solstice. Antarctic researchers recently found that there is
a reduction of photosynthesis for populations sampled inside the ozone hole. Unpublished results
indicate a 6%-12% reduction in water column primary productivity associated with a 43 %
decrease in atmospheric ozone (from 350 DU outside the hole to 200 DC inside the hole).
Inhibition could be related to changes in the ratio of UV-B/(UV-A + Visible + UV-B) radiation as
well as the quantity of solar UV-B radiation. Because adaptation occurs on many time scales, it is
impacts. not possible to accurately extrapolate from these short-term incubations at fixed depth to long-term
Although we know that photosynthesis will decline to some degree, the dose/response curve is not
yet accurately known. Under natural conditions, cells do not remain at fixed depths; rather they are
carried around by the mixing water. To follow cells over time, it is necessary to enclose them in
bottles and incubate on shipboard or at fixed depths in the water column. The effect of this
2
enclosure can at best be approximated. Because of this, researchers are looking for natural
indicators of UV-B status, which could be assessed without incubating samples in bottles.
Antarctic phytoplankton blooms form each spring as the marginal sea ice melts to form a lens of
relatively stable water. While biomass is generally highest during late spring and early summer
(Nov. - Jan.), these blooms are typically initiated in the early spring, during the ozone hole. Cells
are likely to be particularly vulnerable because the stable water conditions concentrate these shade-
adapted cells near the surface where UV-B levels are highest.
Differences in sensitivity among species
Species vary in their sensitivity to UV-B, and even closely-related species can differ dramatically.
POSSIBLE CONSEQUENCES OF UV-B INCREASES FOR THE FOOD CHAIN
Changes phytoplankton species composition
Differential sensitivity may result in changes in species composition even if total water column
productivity remains unaffected. While it appears that species composition will vary in some way,
it is not yet clear how it will change.
Natural variability is a problem with most global-change issues, and is particularly so when
looking for ozone-related changes in natural systems. Because movement of the ozone hole results
in large and rapid changes in UV-B levels which may pass over within a couple of days, adaptation
over the period of ozone depletion may not be complete, and unaffected seed populations may exist
in nearby areas. Cells might not be able to adapt to their full potential during one ozone-hole pass,
and might revert to a pre-hole physiological state after the hole passes over. If so, the community
would exist in a constant state of disequilibrium.
The ozone hole presently occurs each spring just as the sea ice is melting, and dissipates before
summer. Large seasonal changes in light, nutrients and water column stability unrelated to ozone
could provide large and presumably different selective pressures. For instance, spring blooms are
initiated by the release of cells from melting sea ice. These low-light adapted species may not be
the most resistant to springtime ozone-related increases in UV-B radiation, and they are certainly
not acclimated at the time of their release even if they do have the capability to acclimate.
Changes in higher trophic levels
Changes in the abundance, size distribution, or nutritional value of primary producers will affect
higher trophic levels by reducing feeding efficiency and potentially causing nutritional deficiencies.
Species composition might be shifted towards different size or nutritional classes, and this could
reduce food availability to higher trophic levels even if total primary production remained at past
levels. Thus, changes in the species composition of the primary producers could cascade through
a food chain even if the higher trophic levels are not directly affected by UV damage and even if
total primary production is not affected. Bottle experiments using natural populations are
necessarily short term and consequently inadequate for determining long-term impacts, including
changes in species composition and ecological consequences.
SUMMARY
In conclusion, recent studies confirm earlier findings and demonstrate that UV-B radiation is
harmful at both pre- and post-ozone hole levels. The effect of UV-B on marine phytoplankton will
increase with decreasing stratospheric ozone, and the effect of UV-B on Antarctic marine
phytoplankton is likely to increase if the ozone hole gets deeper, bigger or lasts longer. We know
more now than we did 10 years ago about UV-B effects on marine phytoplankton, but we do not
yet know enough to accurately predict population or ecosystem responses to increases in solar UV-
B radiation..
3
Partial Bibliography, 1986-present
Bidigare, R.R., 1989. Potential effects of UV-B radiation on marine organisms of the Southern
Ocean: Distributions of phytoplankton and krill during austral spring. Photochem. Photobiol. 50:
469-477.
Carreto, J.I., M.O. Carigan, G. Daleo & S.G. Marco, 1990. Occurrence of mycosporine-like
amino acids in the red tide dinoflagellate Alexandrium excavatum. UV protective compounds? J.
Plankton. Res. 12: 909-921.
El-Sayed, S., F.C. Stephens, R.R. Bidigare and M.E. Ondrusek. 1990. Effect of ultraviolet
radiation on Antarctic marine phytoplankton. In: Proceedings of the 5th SCAR Symposium on the
Ecological Changes and the
Conservation of Antarctic Ecosystems (K.R. Kerry and G. Hempel, Eds.), Springer-Verlag,
Berlin, pp. 379-385.
Cullen, J.J. and H.L. MacIntyre, 1990. Influence of UV-B radiation on photosynthesis in sea-
surface films. Mar. Ecol. Prog. Ser. 55: 271-278.
Cullen, J.J. and M.P. Lesser, 1991. Inhibition of photosynthesis by ultraviolet radiation as a
function of dose and dosage rate: Results for a marine diatom. Mar. Biol. submitted.
Döhler, G. 1985. Effect of UV-B radiation (290-320 nm) on the nitrogen metabolism of several
marine diatoms. J. Plant Physiol. 118: 391-400.
Dohler, G. 1987. Effect of irradiation on nitrogen metabolism in marine diatoms and
phytoplankton. Oceanis 13: 487-493.
Döhler, G. and I. Biermann, 1987. Effect of u.v.-B irradiance on the response of 15N-nitrate
uptake of Lauderia annulata and Synedra planctonica. J. Plankton Res. 9: 881-890.
Dunlap, W.C. and B.E. Chalker, 1986. Identification and quantitation of near-UV absorbing
compounds (S-320) in a hermatypic scleractinian. Coral Reefs 5: 155-159.
Dunlap, W.C., B.E. Chalker and J.K. Oliver, 1986. Bathymetric adaptations of reef-building
corals at Davis Reef, Great Barrier Reef, Australia III. UV-B absorbing compounds. J. Exp.
Mar. Biol. Ecol. 104: 1-10.
Hader, D.-P., 1988. Ultraviolet-B inhibition of motility in green and dark bleached Euglena
gracilis. Current Microbiology 17.
Hader, D.-P. and M. A. Hader, 1988. Inhibition of motility and phototaxis in a green flagellate,
Euglena gracilis, by UV-B radiation. Arch. Microbiol. 150: 20-25.
Helbling, E.W., V. Villafane, M. Ferrario and O. Holm-Hansen, 1991. Impact of natural
ultraviolet radiation on rates of photosynthesis and on specific marine phytoplankton species.
Submitted to Marine Ecology Progress Series.
Karentz, D., J.E. Cleaver, and D.L. Mitchell, 1991. Cell survival characteristics and molecular
responses of Antarctic phytoplankton to ultraviolet-B radiation. J. Phycol. 27: 326-341.
Karentz, D. and L.H. Lutz, 1990. Evaluation of biologically harmful ultraviolet radiation in
Antarctica with a biological dosimeter designed for aquatic environments. Limnol. Oceanogr. 35:
549-561.
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Karentz, D., F.S. McEuen, M.C. Land, and W. C. Dunlap, 1991. Survey of mycosporine-like
amino acid compounds in Antarctic marine organisms: potential protection from UV-B exposure.
Mar. Biol. 108: 157-166.
Lubin, D., G.B. Mitchell, J.E. Frederick, A. D. Alberts, C.R. Booth, T. Lucas, and D.
Neuschuler, 1991. A contribution toward understanding the biospherical significance of Antarctic
ozone depletion. J. Geophys. Res., in press.
Shick, J.M., M.P. Lesser and W.R. Stochaj, 1991. Ultraviolet radiation and photooxidative
stress in zooxanthellate Anthozoa: the sea anemone Phyllodiscus semoni and the octocoral
Clavularia sp. Symbiosis 10: 145-173.
Smith, R.C. and K.S. Baker, 1982: Optical properties of the clearest natural waters (200-800
nm). Applied Optics 20: 177-184.
Smith, R.C. and K.S. Baker, 1989. Stratospheric ozone, middle ultraviolet radiation and
phytoplankton productivity. Oceanography 2(2): 4-10.
Smith, R.C., B.B. Prézelin, K.S. Baker, R.R. Bidigare, N. Boucher,
T. Coley, D. Karentz, S. MacIntyre, H.A. Matlick, D. Menzies, M.E. Ondrusek, Z. Wan and K.
Waters, 1991. Ozone depletion: Ultraviolet radiation and phytoplankton biology in Antarctic
waters. Submitted to Science.
Urbach, F., ed. 1989. The Biological Effects of Increased Ultraviolet Radiation: An Update.
Photochem. Photobiol. 50: 433 - 583.
Voytek, M.A., 1990. Addressing the biological effects of decreased ozone on the Antarctic
environment. AMBIO 19: 52-61.
Weiler, C.S., ed. 1988. Ultraviolet Radiation and Biological Research in Antarctica. NSF 88-
108, National Science Foundation, 28 pp.
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9
TESTIMONY OF
ROBERT C. WORREST, Ph.D.
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
BEFORE THE
COMMITTEE ON COMMERCE, SCIENCE, AND TRANSPORTATION
UNITED STATES SENATE
NOVEMBER 15, 1991
Mr. Chairman, members of the Committee, it is a pleasure to appear before you
today as you consider the United States' activities regarding stratospheric ozone
depletion, as well as the United Nations Environment Programme's assessments
pursuant to Article 6 of the Montreal Protocol on Substances that Deplete the Ozone
Layer. I am Dr.Robert C. Worrest, Program Manager of the U.S. Environmental
Protection Agency's Stratospheric Ozone Research Program, as well as of its Global
Change Research Program. Prior to my move to EPA headquarters, I was Professor
of Radiation Biology at Oregon State University. My research while at Oregon State
University resulted in many publications regarding the impact of enhanced levels of
ultraviolet-B radiation on components of marine ecosystems. Among my publications,
as co-editor, is a book entitled, "Stratospheric Ozone Reduction, Solar Ultraviolet
Radiation and Plant Life." In addition, I have participated as co-author in the 1989
United Nations Environment Programme Environmental Effects Panel Report on the
environmental effects of stratospheric ozone depletion, as well as for the 1991
update.
Depletion of the stratospheric ozone layer is expected to lead to an increase in
the amount of UV-B radiation penetrating toward the earth's surface. Significant
increases in ultraviolet radiation have been observed over Antarctica. This increased
UV flux poses a potentially serious threat in several areas, including human health,
agriculture, silviculture and marine ecosystems. Research indicates that increasing
amounts of UV-B radiation at the earth's surface may lead to a higher incidence of
skin cancer, as well as immunological alterations and cataracts in human populations.
- 2 -
-
Higher levels of ultraviolet radiation are also hypothesized to lead to crop damage and
loss, and perturbations in marine ecosystems with a potential impact on fisheries.
Even with an immediate phaseout of all CFCs and related compounds, current
levels of chlorine loading in the atmosphere commit the world to an unavoidable
decrease in stratospheric ozone well into the next century. Ecological and human
health research, as well as UV-B measurements at the ground, should be pursued in
order to develop adaptive strategies to the inevitable ozone decrease before potentially
serious problems arise.
The goal of EPA's Stratospheric Ozone Research Program is to provide
important, new, policy-relevant information, and yield early warnings of potentially
dangerous impacts from ozone depletion. To develop such policy-relevant
information, the Agency's research program focuses on the impacts of ozone
depletion in areas that have global implications, such as food production and human
health. The Agency also examines the linkages between the problem of ozone
depletion and other issues, particularly global climate change. Many of the trace
gases responsible for ozone depletion are also important greenhouse gases, and other
linkages exist between these two areas. The EPA research program is part of a
coordinated effort including the National Aeronautics and Space Administration, the
United States Department of Agriculture, the Department of Energy, the National
Oceanic and Atmospheric Administration National Marine Fisheries Service, the
Department of Health and Human Services National Institute of Environmental Health
Sciences, and others under the auspices of the Federal Coordinating Council for
Science, Engineering, and Technology Committee on Earth and Environmental
Sciences.
A key challenge for EPA's research program is to target those areas of scientific
uncertainty that are most useful to policy makers in addressing stratospheric ozone
- 3
depletion. This research will contribute to the success of the 1985 Vienna
Convention for the Protection of the Ozone Layer and the subsequent Montreal
Protocol, and to compliance with the conditions of the 1990 Clean Air Act
Amendments.
For the conditions of the Protocol to be successful on a global scale, it is
essential that research be focused on areas that are relevant not only to the United
States and other industrialized nations, but also to developing and newly industrialized
countries. In response to these mandates, EPA has developed an assessment-oriented
research program on stratospheric ozone depletion conducted by the Office of
Research and Development (ORD). ORD's research program is designed to play a
significant role in generating scientific information that is credible to these important
audiences. EPA focuses its research efforts on areas of primary importance to the
mission of the Agency, building upon its own strengths and the strengths of other
national and international organizations.
As decided at the first meeting of the Conference of the Parties to the Vienna
Convention (Helsinki, 26-28 April 1989) in Decision 4 (UNEP/OzL.Conv.1/5), "...the
following activities shall be given priority in the research, observations and transfer
of technology: (d) Research on the human health and biological implications of
ultraviolet radiation changes at the earth's surface. Particular attention must be given
to the impact on food production in the developing world and to development of crop
varieties resistant to higher levels of ultraviolet radiation;
"
A goal of the EPA's $6 million (FY 1992 President's request) Stratospheric
Ozone Research Program is to understand the human health and biological implications
of ultraviolet radiation changes at the earth's surface. Particular attention is given to
the impact on food production in the developing world and to the development of crop
varieties resistant to higher levels of ultraviolet radiation. Research topics covered are
4
(1) human health, (2) wetiand rice ecosystems, (3) marine ecosystems, and (4)
atmospheric and biospheric transport and fate of proposed CFC substitutes and their
degradation products.
U.S. Environmental Protection Agency
Stratospheric Ozone Research Program
Human Health
UV-B radiation is suspected or known to cause significant adverse health
effects, including suppression of the immune system (immunosuppression), ocular
disease, and melanoma and non-melanoma skin cancer.
Summary of Research
1.
Assess Immunosuppressive Effects of UV-B Radiation in Humans
The objective is to assess the nature, extent and potential clinical relevance
of UV-B-induced immunosuppression in normal human subjects.
2.
Assess Effects of UV-B radiation on the Development of Infectious Diseases
The objective is to determine the effects of UV-B exposure on the incidence,
severity and recurrence of a spectrum of infectious diseases in experimental
animals, and to evaluate the effects of UV-B radiation on host resistance and
immunity.
3.
Assess Effect of Elevated UV-B Exposure on the Risk of Photokeratitis
The objective is to identify geographic areas in which ambient levels of UV-B
exposure will exceed the threshold for photokeratitis at progressive levels of
depletion of stratospheric ozone.
5 -
4.
Assess Effects of UV-B Radiation on the Effectiveness of Vaccines in
-
Humans
The objective is to assess the effect of UV-B radiation on the establishment,
effectiveness, and duration of immunization following vaccination.
Wetland Rice Ecosystems
The primary focus of research addressing the response of vegetation at EPA
is to evaluate the impacts of UV-B radiation on rice, the world's most important
food crop. The rice research program evaluates the effects of UV-B radiation on
rice and rice cropping practices, and the effects of global climate changes that may
occur simultaneously with UV-B radiation enhancement. Integrated research tasks
are conducted at the International Rice Research Institute (IRRI) in the Philippines,
and at EPA laboratories and academic institutions in the United States.
Summary of Research
1.
Response of the Wetland Rice Ecosystem to Ultraviolet-B Radiation
The primary objective is to determine the fundamental effects of UV-B
radiation on rice plants and components of the wetland rice ecosystem. Indirect
effects of UV-B radiation on the wetland rice ecosystem will be measured for
important rice diseases, insect pests, weeds, and nitrogen fixers.
2.
UV-B Radiation and the Global Climate Change Scenarios
The main objectives are (1) to link geographic and global climate information
in a Geographic Information System (GIS) environment; (2) to determine the most
critical rice growing areas; and (3) to characterize current and projected future
levels of UV-B radiation, CO2, and temperature for critical rice areas.
- 6
3.
Responses of the Rice Ecosystem to CO2 Enrichment and Temperature
Increases
-
The primary objective of this program is to determine the fundamental
interactive effects of enriched CO₂ and elevated temperatures on rice plants and
rice ecosystems. Of primary concern will be the effects of climate change on rice
yield in the tropics, and components of rice growth and physiology. Ultimately,
interaction studies will be carried out to evaluate the effects of enhanced levels
UV-B radiation in the context of global climate change.
4.
Effects of UV-B Radiation and Global Climate Change on Methanogenesis
The primary objective is to determine the atmospheric feedbacks between
global change, including UV-B radiation, and rice methanogenesis by collecting
baseline data on current methane emission rates from IRRI tropical rice paddies,
and by determining the impacts of global change on methane emission rates from
IRRI tropical rice fields.
5.
Development, Application and Validation of Rice Response Models
The first objective is to develop, apply and validate models that describe the
effects of UV-B radiation and global climate change on rice. The second objective
is to link the models simulating rice ecosystem response to UV-B enhancement and
global climate change with geographic and climate information stored in a GIS
database.
6.
Assessment of Risk to Rice Ecosystems from UV-B Radiation and Global
Climate Change
The primary objective is to assess the risk to rice ecosystems from global
change (including UV-B radiation, CO2, and temperature) through use of models
and GIS.
7
7.
Assessment of Adaptive Strategies for Rice Ecosystem Responses
-
The primary objective is to assess adaptation strategies for the rice
ecosystem in response to global changes. Principal outputs will include (1) reports
assessing the impacts of UV-B radiation on wetland rice ecosystem; (2) reports
assessing the impacts of global climate change on the wetland rice ecosystem; (3)
recommendations regarding the use of plant breeding to adapt to potential effects
of UV-B radiation and global climate change on rice; and (4) recommendations
regarding the use of management practices to adapt to the effects of UV-B
radiation and global climate change on rice.
Marine Ecosystems
Past efforts to understand the effects of stratospheric ozone depletion on
marine ecosystems have addressed (1) the physical variables that determine the
exposure (or dose) to marine ecosystems; (2) the amount of UV-B radiation that
produces biological effects; (3) the direct impacts on the sensitive life stages of
ecologically-important marine organisms; and (4) the extent to which the sum of
the impacts might affect the marine resources significant to humans. The sum of
past efforts suggests that the likelihood of significant impacts from UV-B exposure
to marine environments is real even if it cannot yet be fully quantified.
Summary of Research
1.
Assess the Effects of Chronic UV-B Radiation Exposure on Marine
Ecosystems
The objective is to determine the effects of long-term UV-B radiation
exposure on phytoplankton and zooplankton species, communities, primary and
secondary production, and trace gas fluxes.
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2.
Examine Antarctic Ecosystems Under Current and Enhanced UV-B Conditions
The objectives are to assess the current rates of primary production and
fluxes of radiatively important trace gases, and to assess the impacts on existing
phytoplankton and zooplankton under current Antarctic conditions and under
enhanced UV-B radiation.
3.
Assess the Effects of UV-B Radiation on Fish Eggs and Larvae
The objective is to determine the direct and indirect effects of UV-B radiation
on the survivorship of fish eggs and larvae. To better understand the range of
sensitivity and the mechanisms of damage, UV-B radiation dose-response
relationships will be determined for the eggs and larvae of several commercially
and ecologically important fish species.
Atmospheric Transport and Fate of CFC Substitutes
The goal of this research program is to assess the impact of releasing large
quantities of replacement compounds for ozone depleting CFCs. Major
components of the life cycles of these substitute compounds must be established.
The program objectives are (1) to identify (through laboratory experiments and
theoretical investigations) the chemical and physical parameters controlling
concentrations of CFC substitutes and their oxidation products in air and aqueous
media (including oceans, rivers, and precipitation), and (2) with such data, to
develop models for calculating concentrations based on emission scenarios.
Summary of Research
The approach tracks the chemical evolution of CFC substitutes by
investigating their atmospheric degradation routes, their uptake to aqueous media
and subsequent reactions, and finally their fate during the evaporation process.
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Biospheric Fate and Transport of CFC/Halogen Substitutes
-
The goals of this research are to (1) define biospheric transformation
pathways and products for CFC/Halogen substitutes in both homogeneous and
heterogeneous systems; (2) determine appropriate rate constants for selected
CFC/Halogen substitutes (and their appropriate corresponding daughter products);
(3) derive algorithms to describe environmental transformations of these
compounds for use in predictive models; (4) refine terrestrial and aquatic ecological
risk assessment models; and (5) carry out the appropriate risk assessments.
Summary of Research
This research will enable researchers to (1) determine reaction pathways and
fate constants for selected HFCs/HCFCs, their tropospheric oxidation products, and
their their fate constants; (2) to determine reaction pathways and rate constants
for selected terpene cleaners; and (3) to carry out ecological risk analysis on select
compounds in each class of substitutes, as fate and toxicity data become
available.
In addition to research carried out under the EPA Stratospheric Ozone
Research Program, there is related research performed under the mandate of the
1990 Clean Air Act Amendments. What follows is a description of that research:
Engineering Plan for Stratospheric Ozone Protection
The goal of of this program is to provide scientific/engineering information on
potential controls for stratospheric ozone protection (particularly pollution
prevention) in support of the 1990 Clean Air Amendments, the 1990 revised
Montreal Protocol, and the potential needs of accelerated phaseout schedules. The
program's primary emphases will be to evaluate (in cooperation with the private
sector) long-term, environmentally acceptable alternatives to ozone-depleting
- 10 -
substances, products made with such substances, or products containing such
substances:
Summary of Research
The research areas to be addressed include the following: determining the
most cost-effective ways to comply with the Montreal Protocol and Clean Air Act
Amendments limiting ozone depleting compounds; complying with international
treaty provisions on technology transfer and trade; increasing international
participation in the Montreal Protocol; assuring that transition away from ozone
depleting compounds does not create new environmental problems; development
of cost-effective energy efficient substitutes; assessing the benefits and costs of
developing a national recycling program; and evaluating additional potential
requirements in the Protocol and Clean Air Act Amendments. However, by seeking
rapid solutions, potential risks are posed to health and safety. The greenhouse
issue is one important consideration because many replacements for CFCs and
HCFCs are also greenhouse gases. Clean Air Act Amendments require that
environmental effects such as these be addressed.
The breadth of the studies is wide. Some studies require that the specific
use of a chemical be evaluated to determine its exact function and mechanics.
Next, scoping plans are devised to address potential replacements (ex. Halon-1301
in total flooding fire extinguishment systems). Other studies are at the
experimental stage, such as chemical replacements for aerosols). Other studies
might provide assessment of a given solution for compliance with EPA regulations
under the Clean Air Act Amendments. New chemicals which theoretically may be
applicable must be synthesized, purified, and evaluated for their appropriate
properties (i.e., compared to properties that are believed to be necessary for
successful use in a given application). EPA is working with other government
agencies, academia, and industry to assess, evaluate, develop, and implement
- 11 -
solutions as appropriate. In domestic home refrigerator/freezers, EPA is working
with the Association of Home Appliance Manufacturers; individual refrigerator
manufacturing companies (Amana and Whirlpool); chemical companies (Grace and
Allied); research organizations (Oak Ridge National Laboratory); and universities
such as Maryland, Purdue, Illinois, and lowa State. These efforts involve modeling,
component evaluation, and integrated system hardware modification and testing.
In non-home refrigeration areas, a similar approach is starting, and efforts are
expected to expand in 1992. In addition to domestic efforts, EPA is working with
developing countries to help assess their needs and transfer technology, to assist
in their efforts to reduce use of these chemicals. For example, research on home
refrigerator/freezers has already involved some cooperation with India and The
People's Republic of China.
EPA has already completed a project setting a standard for the recycling of
refrigerants for automotive use in cooperation with the Mobile Air Conditioning
Society, Motor Vehicle Manufacturers Association, Society of Automotive
Engineers, and others. As a result of this effort, the Alliance for Responsible CFC
Policy successfully petitioned EPA to establish a national recycling program for all
refrigerants. In pursuing this approach, the Office of Research and Development
works closely with the Office of Air and Radiation to develop a sensible solution.
Thank you Mr. Chairman.