AN  ASSESSMENT OF THE RISKS OF
                     STRATOSPHERIC MODIFICATION
                     Volume  I:  EXECUTIVE SUMMARY
                             Submission to the

                          Science Advisory Board
                   U.S.  Environmental  Protection Agency
                                    By

                        Office of Air and Radiation
                   U.S.  Environmental  Protection Agency
                               October 1986
                     Comments should be addressed  to:

                              John S. Hoffman
                U.S. Environmental Protection Agency, PM 221
                            401 M Street, S.W.
                          Washington, O.C.  20460
                                   USA
The following report  is being submitted to the Science Advisory Board and to
the public for review and comment.  Until the Science Advisory Board review
has been completed and the document is revised,  this assessment does not
represent EPA's official position on the risks associated with stratospheric
modification.  This report has been written as part of the activities of the
EPA's congressionally-established Science Advisory Board, a public group
providing extramural  advice on scientific issues.  The Board is structured to
provide a balanced independent expert assessment of scientific issues it
reviews, and hence, the contents of this draft report do not necessarily
represent the views and policies of the EPA nor of other agencies in the
Executive Branch of the Federal Government.  Until the final report is
available, EPA requests that none of the information contained in this draft
be cited or quoted.  Written comments can be sent to the Science Advisory
Board and would be appreciated by November 14, 1986.  Public comments should
be submitted to John Hoffman by December 15, 1986.
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SUMMARY

    Rising concentrations of chlorofluorocarbons (CFCs)  and Halons have the
potential to deplete stratospheric ozone and to allow additional quantities of
the biologically damaging part of the ultraviolet radiation spectrum (UV-B) to
penetrate to the earth's surface, where it would harm public health and the
environment.  While considerable scientific uncertainties remain, substantial
advances have taken place in understanding of this issue since the development
of the theory linking CFCs to ozone depletion in 1974.

    Over the past decade, non-aerosol CFC use has risen as the global economy
has grown.  A variety of studies indicate that the long-term growth of CFCs,
in the absence of additional regulation, is likely to be between 1% and 4%
annually.

    Atmospheric concentrations of other trace gases (e.g., carbon dioxide,
methane, and nitrous oxide) are also growing.  The sources of carbon dioxide
increases can be linked primarily to expanded use of fossil fuels, and
secondarily to deforestation.  In contrast, far less is understood about the
sources and sinks of methane and nitrous oxide.  Unlike CFCs and halons, these
gases either add to the amount of ozone or reduce the rate of depletion.  Like
CFCs, these gases are greenhouse gases that are predicted to increase global
temperatures and change global climate.  Since future trends in emissions of
these gases are important factors in determining ozone modification and
climate change, assumptions about their growth must be carefully considered.

    Models of stratospheric chemistry and physics are used to predict future
changes in the ozone layer.  While these models fail to accurately reflect all
the complex forces which interact in the atmosphere to create and destroy
ozone, nonetheless, they represent the most advanced tools for understanding
possible  changes in the ozone layer that could be related to future scenarios
of trace  gases.  One-dimensional models predict that average global ozone will
decline for all scenarios in which CFCs grow.  Two-dimensional models analyze
ozone depletion for seasons and  latitudes.  These models predict depletion at
higher  latitudes even if CFC use is reduced to  1980  levels and other trace
gases continue to grow at recent rates.

    Model estimates of total column depletion are sensitive to the continued
release of  greenhouse gases that counter ozone  loss.  If an assumption  is made
that emissions of these gases are eventually  limited  in order to  reduce the
magnitude of  future global warming, the depletion expected  froo  any scenario
of CFC  emissions would be  larger.

    Because the current models oversimplify or  fail  to  include processes  that
occur in  the  atmosphere,  a critical question  relates  to how useful they are  as
a predictive  tool.  One method of testing  their validity  is to  compare  their
predictions against observations of the atmosphere.   Models currently  closely
reproduce most  atmospheric measurements, but  fail to accurately  reproduce
some, including ozone  in  the upper stratosphere and  the  rapid depletion of
ozone in  Antarctica  in  the  last  six years.   These  inconsistencies lower our
                           * * *  DRAFT FINAL  * * *

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                                   -2-
confidence in models, making us less certain that they are not underpredicting
or overpredicting depletion.  At this time, however, analysis of Antarctic
data has not proceeded far enough to justify abandoning current models as the
best tools for risk assessment.

    Many inputs to these models are based on laboratory measurements.
Uncertainty about the accuracy of these measurements is one potential  area
responsible for the inadequacies of current model predictions.  Analyses of
the implications of this class of uncertainties indicate that if CFCs  grow,
there is only a small chance of no depletion even if laboratory measurements
change within the ranges tested.  The chances of a depletion significantly
greater than the average predicted appears larger than the chances of  one
significantly smaller.

    If depletion in column ozone takes place, increases will occur in basal
and squamous skin cancer cases and are considered likely for melanoma skin
cancer.  Deaths from these cancers would also increase.  If depletion occurs,
additional cataract cases could be expected, along with increased suppression
of the immune system.  The effect of this  immune suppression on infectious
diseases like herpes and leishmaniasis would be to reduce the body's capacity
to prevent spread or outbreaks.  Little is known about effects on other
cutaneous infectious diseases.

    While quantitative assessments of the  risk to crops and terrestial and
aquatic ecosystems from higher UV-B associated with depletion are not yet
possible, evidence appears to  indicate that significant risks exist.  While
some cultivars of plants are less susceptible and photorepair mechanisms may
reduce losses, field tests to  date have shown damaging effects on yield.   In
the case of aquatic organisms, experimental design  is far more complicated.
Initial studies suggest that some species  are damaged more than others.  The
net effect on productivity and any implications  for the aquatic food chain
cannot yet be determined.

    If ozone depletes, polymers would be expected to degrade more quickly,
although quantitative estimates are available for only one polymer.  Finally,
based on one study, depletion  is predicted to increase both tropospheric ozone
(i.e., smog) in urban areas and the production of hydrogen peroxide (an acid
rain precursor).

    Increases  in CFCs and other trace gases  and  resulting stratospheric
modification all are  expected  to contribute to global wanning  and climate
change.  According to the National Academy of Science  the magnitude of  future
warming  is very uncertain.  The currently  accepted  range  is  3°C + 1.5°C  for
doubled  C02 or  its equivalent  in radiative forcings from other gases.   Cloud
response to warming  is  the  major uncertainty with regard to  the magnitude  of
warming.  The  timing  of the warming  is  also uncertain.  Oceanic heat
absorption  is  the major question with  regard to "the speed which the world's
temperature can expect  to  increase.

    Global warming  is  likely  to cause  thermal  expansion of the oceans  and
alpine  melting, raising sea level.   The contribution of ice  deglaciation  to
sea level  rise is much  more uncertain.
                           * * *  DRAFT FINAL  * * *

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    Sea level rise can be expected to innundate land, especially wetlands,
erode recreational beaches, and cause increased flooding and saltwater
intrusion into freshwater areas.  River delta areas are expected to be most at
risk.  Case studies in two U.S. cities indicate that sea level rise can be
expected to cause significant economic damage, some of which could be
mitigated by anticipatory actions.

    The climate change (e.g., shifts in rainfall, storm tracks, etc.) that
would be associated with global warming is more difficult to predict than sea
level rise, as are the effects of that climate change.  Nevertheless, studies
suggest that forests, water resources, agriculture, and health will all be
affected.

    An integrated analysis of the likely emissions, atmospheric response, and
effects (based on a one-dimensional model) indicates that under the central
case assumptions the U.S. can expect 40 million additional skin cancer cases
and 800,000 deaths for people alive today and those born during the next 88
years if there is no further action taken to limit CFCs.  Two-dimensional
models, because they include estimates of depletion by latitude, may be more
suitable for estimating impacts.  Preliminary analysis using these models
suggests that the effects could be twice as high.  In addition, estimates of
ozone depletion would be much higher if greenhouse gases are eventually
limited, approximately doubling for a case which assumed that greenhouse gases
are limited in order to hold warming to 3°C (assuming 3°C for doubled C02; the
actual limitation imposed by such a reduction in greenhouse gases could be
1.5°C or 4.5°C, based on the NAS range).

    Integrated analyses show that estimates of damages are sensitive to the
rate of CFC and other trace gas growth.  Quantitative estimates of damage are
also sensitive to assumptions underlying relationships between exposure and
impact in each of the effects area.

    A further underlying uncertainty exists about  risk estimates  -- no
experiments can be conducted with the earth to validate these models.  Thus,
there is no guarantee that models are not under or overpredicting the
magnitude of the risks.
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SUMMARY OF FINDINGS

1.  IN THE ABSENCE OF REGULATION, ATMOSPHERIC CONCENTRATIONS OF POTENTIAL
    OZONE-DEPLETING CHEMICALS ARE LIKELY TO INCREASE WITH WORLD ECONOMIC
    GROWTH.

    la.   Estimates of chlorofluorocarbons (CFCs) 11 and 12 based on economic
          analysis indicate that average long-term growth is likely to be 2.5%
          per year; growth of CFC 113 and 22 is expected to be higher.

    Ib.   While significant uncertainty surrounds long-term growth, estimates, a
          variety of studies indicate that growth is unlikely to be negative
          nor greater than 5%; several studies indicate that a long-term growth
          rate between 1.2% and 3.8% is more likely.

    Ic.   Halon 1211 and  1301, two brominated fire extinguishants, may grow
          fast enough to  become significant contributers to ozone depletion.

2.  CONCENTRATIONS OF OTHER TRACE SPECIES (CARBON DIOXIDE. METHANE. NITROUS
    OXIDE) THAT COUNTER  OZONE DEPLETION ARE ASSUMED TO INCREASE AT
    APPROXIMATELY THE SAME RATE AS IN RECENT YEARS.  THESE TRACE SPECIES ARE
    ALSO  GREENHOUSE GASES THAT WILL ADD TO GLOBAL WARMING.

    2a.   A variety of studies based on future fossil fuel consumption have
          estimated carbon dioxide  (C02) growth.  Assuming moderate economic
          growth and technological  change, C02 emissions were predicted to grow
          at 0.6% annually.

    2b.   Recent measurements of nitrous oxide (N20) show growth of 0.25% per
          year.  Continuation of the trend was used in the central case.

    2c.   Recent measurements of methane  (CH4) show 1.0% per year increase.
          Continuation of the trend was assumed  in the central case.

    2d.   Significant uncertainty  surrounds all  these trends.  Because  little
          is understood  about the  sources and sinks of methane, and it has a
          relatively short  atmospheric  lifetime,  assumptions about future
          trends of this gas  are particularly uncertain.

    2e.   The  standard assumption  the modeling community has used in  developing
          scenarios has  been  that  long-term projections of trace gases  that
          counter ozone  depletion  will  not be  limited by future decisionmakers
          in order to  reduce  the  magnitude of global warming.

 3.  MODELS OF THE STRATOSPHERE  PREDICT DEPLETION FOR SCENARIOS IN WHICH CFCS
    AND OTHER TRACE GASES  CONTINUE TO  GROW.  MODELS PREDICT DEPLETION  AT
    HIGHER LATITUDES  EVEN  FOR  SCENARIOS  IN WHICH THE EMISSIONS OF POTENTIAL
    OZONE DEPLETERS ARE LOWER  THAN TODAY'S EMISSIONS.

    3a.   While  different models  produce  slightly different  changes  in  ozone
          for  the  same scenario,  they generally  provide  roughly consistent
          estimates.
                           * * *  DRAFT FINAL  * * *

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    3b.  Estimated changes in ozone levels are dependent on assumptions about
         trace gas growth.  For example, if CFCs do not grow and other trace
         gases continue to increase, greater amounts of ozone are likely.

    3c.  Based on a two-dimensional model, depletion with 3* growth of CFCs
         and standard assumptions for gases that counter depletion is
         predicted to be 7% by 2030 at 50°N.

4.  PREDICTED OZONE DEPLETION IS SIGNIFICANTLY GREATER FOR SCENARIOS IN WHICH
    GROWTH IN C02. N20. AND CH4 IS NOT ASSUMED TO CONTINUE UNABATED FOR THE
    NEXT CENTURY.

    4a.  Depletion estimates would be doubled if greenhouse warming were
         ultimately limited to 3°C (the limitation assumes 3°C temperature
         sensitivity for double CO.; the actual limit could vary by +50%).

    4b.  Depletion would be even greater for a more stringent temperature
         limit.

5.  A NUMBER OF INCONSISTENCIES BETWEEN OBSERVATIONS AND PREDICTIONS LOWERS
    OUR CONFIDENCE THAT MODELS ARE NOT UNDER OR OVER PREDICTING DEPLETION.
    HOWEVER. CURRENT MODELS DO ACCURATELY REPRESENT MANY ELEMENTS OF THE
    ATMOSPHERE AND STILL APPEAR TO BE THE MOST RELIABLE METHOD OF ESTIMATING
    THE RISKS ASSOCIATED WITH FUTURE SCENARIOS OF TRACE GAS EMISSIONS.

    5a.  Models reproduce most observations of the current atmosphere
         relatively well, supporting the belief they can usefully be used as
         tools to predict the future.

    5b.  Discrepancies exist between some predictions and both observations
         and measurements of various species in the current atmosphere thus
         lowering our confidence that the models will not under or over
         predict depletion.

    5c.  From  1970-83 models have predicted depletion in upper  layers of the
         stratosphere.  This is  consistent with actual measurements at 40 km.

    5d.  Analyses of the  uncertainties  of  laboratory measurements used as one
         class of inputs  to atmospheric models  indicate that  if chlorine
         grows, depletion is likely.  The  analyses also demonstrate  that a
         depletion significantly larger than that yielded by  the standard
         inputs  is more  likely than  a depletion that is significantly  lower.

6.  THE FAILURE OF MODELS TO PREDICT THE ANTARCTIC OZONE DEPLETION RAISES
    SERIOUS QUESTIONS ABOUT MODEL RELIABILITY.  HOWEVER. UNTIL  A BETTER
    UNDERSTANDING AND ANALYSIS OF THIS  PHENOMENON IS ACHIEVED.  CURRENT MODELS
    ARE STILL  THE MOST APPROPRIATE TOOLS FOR RISK ASSESSMENT.

    6a.  The seasonal Antarctic  depletion  has been verified by  several
         different types  of  instruments;  models with conventional  chemistry
         cannot  explain  the Antarctic depletion.
                           * * *  DRAFT FINAL  * * *

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                                  -6-
    6b.   Several chemical and dynamical theories have been proposed to
         explain the seasonal Antarctic depletion.   Current observations are
         insufficient to determine which,  if any, are true or false.

    6c.   At this time, it is unclear whether the seasonal Antarctic depletion
         is a precursor to a general atmospheric phenomenon, will be an
         anomaly that remains in this unique and geographically isolated
         region, or will disappear altogether.

    6d.   Satellite measurements from Nimbus 7 appear to indicate a depletion
         in recent years in the Arctic.  The scientific community has not
         analyzed this data sufficiently to reach a consensus on the validity
         of the data as its been interpreted, its meaning, or even to
         conclude it is not part of a cyclical trend.  Until this data and
         its interpretation are verified,  and causality is determined, it
         cannot be used as a basis for considering the risks from CFCs.

7.  OZONE DEPLETION WILL CAUSE AN INCREASE IN SQUAMOUS AND BASAL SKIN
    CANCERS; A GREATER RISE WILL OCCUR IN SQUAMOUS SKIN CANCER.

    7a.   Squamous skin cancer can be anticipated to rise between 2 and 5
         percent for each one percent depletion of ozone.  Squamous skin
         cancer is generally more serious than basal cancer and proves fatal
         in a higher percentage of cases.

    7b.   Basal skin cancer can be anticipated to rise between  1 and 3 percent
         for each one percent depletion of ozone.

    7c.   Although only a very small percentage of cases of these skin cancers
         result in mortality, the large number of additional cases will
         aggregate to create a substantial increase in total number of skin
         cancers.

8.  OZONE DEPLETION IS LIKELY TO CAUSE AN INCREASE IN MELANOMA SKIN CANCER.
    ALTHOUGH SOME UNCERTAINTY REMAINS ABOUT THIS CONCLUSION.

    8a.  Melanoma is  a deadly form of skin cancer that currently kills 5,000
         people in the United States a year.

    8b.  Although conclusive evidence does not yet exist,  many factors
         suggest that UV-B  radiation plays a substantial  role  in the
         incidence of melanoma skin cancer.

    8c.  Melanoma incidence  is likely to rise between  1  and  2  percent  for
         each one percent  increase  in ozone depletion.

    8d.  Melanoma mortality  is likely to increase about  0.8  to 1.5 percent
         for each one percent  increase in ozone  depletion.
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 9.   OZONE DEPLETION IS  LIKELY TO SUPPRESS  THE  IMMUNE SYSTEM  OF HUMANS.

     9a.    Laboratory evidence and case  studies  demonstrate that exposure to
           UV-B radiation has  the effect of suppressing the immune system.

     9b.    Although quantitative estimates  are  impossible, depletion is  likely
           to increase outbreaks of herpes  and  the severity of leishraaniasis.

     9c.    The impact of immune suppression on  other infectious cutaneous
           diseases has  not yet been studied.

10.   OZONE DEPLETION IS  LIKELY TO CAUSE  AN  INCREASE IN CATARACTS.

     lOa.   Laboratory evidence and epidemiology studies have  shown that
           exposure to UV-B radiation is one cause of cataracts.

     lOb.   A 1% ozone depletion is likely to cause between a  0.3% to 0.6%
           increase in cataract cases.

     lOc.   In the U.S.,  cataracts are treatable, but are still the third
           leading cause of blindness.  In developing countries they are also
           a primary source of blindness.

11.   OZONE DEPLETION IS LIKELY TO REDUCE CROP YIELD IN CERTAIN CULTIVARS. AND
     ALTER COMPETITION BETWEEN PLANTS.  THE DIMENSIONS OF THE CHANGES ARE NOT
     YET QUANTIFIABLE.

     lla.   Information on the effects of increased UV-B exposure on plants is
           very limited.  Few plants have been tested under natural conditions.

     lib.   Some cultivars appear to be more susceptible to UV-B than others.
           Inadequate information exists to determine why this occurs and if
           selective breeding could be an effective defense to mitigate
           damages from ozone depletion.

     lie.   Two out of three cultivars of soybeans tested were sensitive to
           enhanced UV-B.  One cultivar that was tested extensively showed a
           yield loss of up to 25% for a 20% depletion.

     lid.   Field experiments show UV-B may affect competition between plant
           species.  Ozone depletion, particularly  in conjunction with other
           stresses, might alter ecosystems in ways not yet understood.

12.  OZONE DEPLETION IS LIKELY TO ALTER AQUATIC ECOSYSTEMS AND  POSSIBLY AFFECT
     THE AQUATIC FOOD CHAIN.  THE DIMENSIONS OF THE  POSSIBLE CHANGE ARE NOT
     YET QUANTIFIABLE.

     12a.  Limited experiments suggest  that increased UV-B can  alter the
           community composition of phytoplankton  that  form the base of the
           aquatic food web, can curtail the survival of zooplankton, and can
           shorten breeding seasons.
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     12b.   Uncertainties in the lifecycles of these organisms prevents
           quantitative estimation of effects, although some data exist which
           suggest that relatively low thresholds of  tolerance to increases
           in UV-B could affect commercially important species.  However,
           movement to limit exposure, and turbulence or mixing may limit
           damage to organisms.

13.   OZONE DEPLETION WOULD DEGRADE POLYMERS. SHORTENING THEIR USEFUL LIFE.
     COUNTERMEASURES WOULD ADD COST AND POSSIBLY REDUCE PRODUCT QUALITY.

     13a.   Current usage shows that UV-B damages physical and chemical
           properties of certain polymers.

     13b.   Stabilizers can be added to mitigate damage from increased UV-B,
           but at a price and possible loss in product quality.

     13c.   Uncertainty exists about effects of higher UV-B on polymers due to
           a lack of an adequate experimental data base relating UV-B dose to
           degradation.

     13d.   One study that examined the effects of UV-B on polyvinylchloride
           showed substantial losses from future ozone depletion.

14.   BY INCREASING UV-B. OZONE DEPLETION MAY  INCREASE URBAN OZONE. A
     POLLUTANT REGULATED UNDER THE CLEAN AIR  ACT.  IT MAY ALSO INCREASE
     HYDROGEN PEROXIDE. AN ACID RAIN PRECURSOR.

     14a.   The only study on this issue stated that increased UV-B could  cause
           increases in ground-based ozone  (i.e., smog).  In addition, because
           the ozone formed earlier  in the  day,  it would affect  larger
           populations.

     14b.   It also showed that global warming could enhance the  negative
           effect of enhanced UV-B on ground-based oxidants.

     14c.   The study also predicted  that  hydrogen peroxide production was
           extremely sensitive to increased UV-B.

     14d.  Continued studies on the  effects of UV-B on ground-based oxidants
           and hydrogen peroxide  formation  are needed to validate  this  initial
           effort.

15.  INCREASES IN TRACE SPECIES THAT MODIFY OZONE ARE ALSO EXPECTED TO  CAUSE  A
     SIGNIFICANT GLOBAL WARMING.

     15a.  The National Academy of  Sciences estimated a warming  or 3°C  +
           1.5°C for doubled C02.   This  range is attributable  to uncertainty
           as to whether  changes  in clouds  will  amplify or dampen global
           warming.
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                                   -9-
     15b.   The tuning of  the warming  is  expected  to  lag  the emission  of  gases
           by 10 to 40 years.   Uncertainty  about  the timing is due  to a  lack
           of knowledge about  the  rate of oceanic heat absorption.

     15c.   Changes  in stratospheric water vapor would raise global
           temperatures.   Changes  in  vertical  structure  of ozone would add to
           warming  until  depletion became  large,  at  which point  it  would begin
           decreasing temperatures.

     15d.   Due to deficiencies in  model  representations  of a  variety  of
           phenomena, regional characteristics of the climate change  that
           would accompany the global warming  are largely uncertain.   In
           general, temperatures will increase the further one goes from the
           equator, the hydrological  cycle  will  intensify, and areas  of
           wetness  and dryness will shift.   Little else  about climate changes
           can be stated  with  certainty.

16.   SEA LEVEL IS LIKELY  TO RISE AS A RESULT OF  GLOBAL VARMING.   PREDICTIONS
     ARE UNCERTAIN. BUT SEVERAL STUDIES  HAVE ESTIMATED A RANGE FROM 50 CM TO
     200 CM BY 2100 IF GREENHOUSE  GAS GROWTH IS  NOT CURTAILED.

     16a.   The primary cause of sea level  rise will be thermal expansion and
           alpine ice melting.  Only for the higher estimates will  Antarctic
           deglaciation contribute significantly.

     16b.   Sea level rise can be expected to innudate asd  erode  coastal  land,
           to increase flooding, and to produce  saltwater  intrusion into
           freshwater areas.

     I6c.   Wetlands and river deltas will be most adversely  affected.  By 2100
           the U.S. could lose up to 50% to 80% of its  coastal wetlands.

     16d.   Preliminary studies suggest adverse economic  effects,  which could
           be substantially reduced by anticipatory planning.

17.   GLOBAL WARMING CAN BE EXPECTED TO ALTER REGIONAL CLIMATES AND AFFECT
     MANY ASPECTS OF THE  ENVIRONMENT.

     17a.  Based on analyses of past climatic changes of roughly similar
           magnitude  (but which occurred over far longer periods of time),
           forests will be altered significantly.

     17b.  Limited assessments suggest that important changes in farm
           productivity can be expected throughout the world.

     17c.  The  location and design of water resource projects are  likely  to be
           altered by  climate  change.

     17d.  Human morbidity and mortality could be influenced.  According  to
           the  one study on this  issue, in the absence of full acclimatization
           (which  is  doubtful  in  built-up cities  like New York) mortality from
           extreme temperatures is likely to  increase.


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                                   -10-
18.   FOR THE MOST LIKELY ASSUMPTIONS ABOUT EMISSIONS. ATMOSPHERIC RESPONSE.
     AND EFFECTS. SIGNIFICANT IMPACTS ARE EXPECTED FOR HUMAN HEALTH AND THE
     ENVIRONMENT.  HOWEVER.  MAJOR UNCERTAINTIES EXIST ABOUT EACH AREA.
     CONSEQUENTLY THE SENSITIVITY OF RISK ESTIMATES TO THOSE UNCERTAINTIES
     MUST BE EXAMINED.   ESTIMATES OF RISKS IN THIS STUDY ASSUME NO ACTION IS
     TAKEN TO REDUCE DEPLETION.

     18a.  For the central case  (2.5% CFC growth, 0.6% C02 growth, and recent
           trends for other gases), an additional 40 million skin cancer cases
           and 800,000 deaths are projected for people alive today and those
           born in the next 88 years in the United States.  An additional 12
           million cataract cases could occur.

     18b.  The earth's equilibrium temperature would rise from 3°C to 9.5°C by
           2075.

     18c.  Estimates of risk from ozone depletion are highly sensitive to the
           assumptions about growth in greenhouse gases that counter such
           depletion.  Limiting equilibrium global warming to 3°C (assuming
           3°C sensitivity for doubled C02) would more than double the risks
           of ozone depletion from CFC and haIon growth.

     18d.  Estimates of risks are highly sensitive to CFC and halon growth
           rates.  If one assumes half the CFC growth rate of the standard
           case, that is 1.2% instead of 2.5%, estimated damage can be reduced
           by 90%.  If one assumes a growth rate of  3.8%, estimated damages
           would increase 400%.

     18e.  Damage estimates are sensitive to the atmospheric model used.  With
           two-dimensional models, estimates of all  damages would
           approximately double.

     18f.  Uncertainties about dose-response relationships lead to changes  in
           estimates of the number of cases by 35% for nonmelanoma and by  as
           much  as 60% for melanoma.

     18g.  Quantitative estimates of damages for other areas  -- crops,
           aquatics, ground-based ozone, sea level rise,  and polymers  --
           cannot yet be calculated.
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INTRODUCTION

    Moving from the surface of the earth towards  space,  the temperature  falls
until the stratosphere is reached at 10-15  kilometers  above the earth's
surface.  At this point temperatures begin  to rise  (Exhibit 1).  The
stratosphere sustains unique conditions in  which  ozone (03) is constantly
produced and destroyed, providing an abundance that  varies  latitudinally,
seasonally and annually around long-term means.

                                EXHIBIT 1

        Temperature Profile and  Ozone Distribution  in the Atmosphere
                         1  .
     Small  quantities of chlorine, nitrogen, hydrogen, or bromine can combine
 in chemical reactions with ozone molecules to produce bimolecular oxygen
 (02).   These substances act  as  a catalyst.  They are freed following a series
 of reactions and can repeatedly combine with ozone.  Chlorofluorocarbons,
 methyl chloroform and carbon tetrachloride can carry chlorine to the
 stratosphere,  halons can  carry  bromine, and nitrous oxide can carry nitrogen.
 The chlorine and bromine  from chlorofluorocarbons and halons act as strong
 depleters  of ozone.  Nitrous oxide,  in the face of growing chlorine, can
 interfere  with the destruction  of ozone by chlorine.  Carbon dioxide cools the
 stratosphere,  reducing the destruction rate of ozone.  Methane creates ozone
 in the troposphere (which contains  10% of the column ozone) and interferes
 with ozone destruction in the stratosphere.  It also increases stratospheric
 water vapor.  All of these molecules are greenhouse gases.  Exhibit 2
 summarizes their atmospheric effects.
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                                   -12-
                                EXHIBIT 2

                Stratospheric  Perturbants and Their Effects
Nitrous oxide
Chlorofluorocarbons
                         Direct Effect
                           on Global
                        Temperature from
                          Tropospheric
                            Presence
                  Physical
                 Effect on
                Stratosphere
                       Effect on
                     Column Ozone
Carbon Dioxide
Methane
Increases1 Cools2
Increases1 Adds water
vapor;
hydrogen*
Increases ozone3
Increases ozone at
some latitudes',
interferes with
depletion at high
altitudes
Increases
Increases
Adds nitrogen*
Interferes with
catalytic efficiency
of chlorine6
Adds chlorine*   Decreases ozone*
Other Trace Gases
(methyl chloroform,
carbon tetrachloride,
haIons)
Increases3
Adds catalytic
species to
stratosphere*
Decreases ozone*
 1 Ramanathan et al., 1985.

 2 Connell and Wuebbles, 1986.

 1 Isaksen, personal communication.

 * National Academy of Sciences, 1984.

 * Isaksen and Stordal,  1986.

 * National Academy of Sciences  (1984) notes the direct effect of N20 on
 column  ozone.  In the presence  of high levels~of chlorine, N20 may interfere
 with the catalytic cycle  of  chlorine, reducing net depletion (Stolarski,
 personal communication).
                           * *  *  DRAFT FINAL  * * *

-------
                                    •13-
    Depletion of ozone would allow more ultraviolet radiation to reach  the
earth's surface where it could harm human life, plants and aquatic organisms,
and materials.  Less ozone would allow for increased penetration of  the
biologically damaging, shorter, part of the ultraviolet radiation spectrum,
generally referred to as UV-B radiation (Exhibit 3).

                               EXHIBIT 3

          Percent Increase in UV-B Radiation for a 10% Depletion
            29;
   307          317
Wavelength (nanometers)
337   DNA Action Spectrum
     Results for Washington,D.C., for clear skies in June.
     Source:NASA UV model results


 RISING  CONCENTRATIONS OF TRACE SPECIES

     Past emissions of  CFC  11  and 12 have  caused a rise in their atmospheric
 concentrations  (Exhibit  4).   These CFCs have been rising at 5% annually.
 Atmospheric measurements show that CFC 113 has grown at 10% annually, and
 Halon 1211 at 23% annually.   Chlorofluorocarbons are used in foam blowing,
 refrigeration and air  conditioning, as a  solvent in electronics and metal
 industries, as  aerosol propellants, and in a variety of specialty
 applications.   Halons  are  used in many applications as a fire extinguishant.
                           * * *  DRAFT FINAL  * * *

-------
                                               -14-
                                           EXHIBIT 4

Historical  Production and Atmospheric  Concentrations of CFC-11  and CFC-12
                                     Historical Production 
-------
                                     •15-
     Based on past trends, emissions  of CFC 11 and 12 have closely tracked GNP,
growing about twice as fast  (Exhibit 5) since the early  1960s.   CFC-113 has
grown  at an even faster pace.

                                 EXHIBIT 5

        Nonaerosol Production Per Capita of CFC-11  and CFC-12  Has Been
                 Correlated With Gross Domestic  Product  (GDP)
                       Per Capita  in  Developed Countries
                                (1962 to 1980)
                      0.8
        Production
             Per     0.6
          Capita

             (kg)    0-4

                      0.2


                         0
                          0246
                                   GDP  Per  Capita
                              (Thousands  1975  US  $)
8
  Production per capita of CFC-11 «nd CFC-12 for nonaeroaol applications has bean correlated with COP per capita In the united
  States ind other OtCO countries.


  Source: CFC production, population, and COP data obtained rraai: Glbos. Nlchael J., (1986). Scenarios of CfC Use:  1985 to 20?5.
        ICF Incorporated, prepared for the g.S. Environmental  Protection Agency.
Concentrations Are  Predicted to Rise

    Market  studies based on extensive  economic analysis by several  authors for
a variety of  geographic areas predict  continued growth in these  chemicals.
Longer-term studies suggest growth  rates  of between 1-4% per year.   Based on
these analyses,  from now until 2050, an average growth of 2.5% appears most
likely.
                           * * *  DRAFT FINAL  * * *

-------
                                             -16-
                                          EXHIBIT 6
                    Short-Term
             Non-Aerosol Projections:
                CFC-11  and CFC-12
                   (1985-2000)
                                                     Long-Term Projections
                                          CFC-11 and  CFC-12  --  World Production
                                                           (2000-2050)
                            I
                 B

                                                      MXWW
                                                             -U  U   U  U   M
                                                                    («|
04)   1.0
                24)
                           4J»    SJO    U
                                     7.0   U
    Source:  "Overview ?»per lor Topic 12:  Projection* 3f ?utor«
          TJ2? Workshop. May 1916
         Based  on these projections, the future growth of CFCs would be below
         historical levels.   Exhibit 7 shows that world GNP per capita in 2050 is
         expected to roughly be equivalent to that of Europe today and slightly more
         than half that of the U.S.  Despite the growth in world income, global CFC use
         would  be considerably less than that of either the U.S. or Europe today.  This
         analysis suggests that, in the absence of regulation, CFC use will continue to
         grow,  but at reduced rates as technological change improves the efficiency of
         use or shifts consumers to alternatives.

                                          EXHIBIT 7

                         Current and Projected Future CFC-11 and CFC-12
                               Use  Per Capita and GNP Per Capita
                               i   IJH  mot
\
                                            (197V
                                              'CSS,
                        •"*»« «M •»«l*nw'l* tMMC M «.*"' *

                        m»x»: 'fti^nt «mm«v P*M*. IwK ft.*
                                    * * *  DRAFT FINAL  * *  *

-------
                                    -17-
    Projections of  future  trends in C02 are based on extensive energy
modelling and analysis.  Exhibit 8 shows a wide range of estimates  based on
varying assumptions  about  economic growth, non-fossil alternatives,  energy
conservation, etc.   For  the purposes of the central case, we have  relied upon
the 50th percentile  case developed by Nordhaus (NAS 1983).

                                 EXHIBIT  8

   Projected Carbon Dioxide  Emissions and Doubling Time of Concentrations
                Cfl'-ben Oi
                Em i ••ton*
                           «nfl DouA I t n?  T <
         C02 eaission projections are shown for EPA (Seidel and Keyei 1983); NAS
         (Nordhaus and Yohe 1983): and Edmonds (Edmonds et al., 1984). The brackets
         indicate the approximate time at which concentrations reach twice the
         pre-industrial level.

     N20 measurements and analysis of  sources and sinks have been more
 limited.  However, recent atmospheric measurements  show a 0.25% annual
 increase.   For the purposes  of  developing scenarios, this annual growth  rate
 has been extended  into the  future.

     Future trends  in methane concentrations are difficult to determine.
 Scientific understanding of its sources and sinks is limited.  However,  its
 relatively short atmospheric lifetime (of about 10 years), suggests that
 changes in emissions over time  could  substantially Influence atmospheric
 levels.  In the absence of  better  information,  we assume that recent  increases
 of approximately  1.0% per year  will continue in the future.

     For evaluating risks, a critical  relationship exists between  emissions and
 atmospheric concentrations.   CFC 11,  12, and 113 have atmospheric lifetimes  of
 75, 110, and 90 years respectively.  This means that about 1/3 of current
 emissions will still be in  the  atmosphere for that length of time into the
 future.  Since current emissions greatly exceed  losses to the stratosphere,
 concentrations will rise even if emissions stop growing  (Exhibit  9).
                            * * *  DRAFT FINAL  * * *

-------
                                   -18-
                               EXHIBIT 9

             Relationship Between Emissions and  Concentrations
            CFC-12:  Emissions
                                             CFC-12 Atmospheric Concentrations
                                             0.40


                                             0.30 •


                                             0.20


                                             0.10 •
         1830
                IMS
                              2100
                                               1830
                                                       1985
                                                                      2100
» ntectlo. o< in i. CTC-12
caae«nr«lou contra (I).
•owe. md lo» turn  SM
                                       lou U) mid b. rnlrad to holt
                                         »itk 11—nfl.d mat»l at
ATMOSPHERIC  RESPONSE

    To explore  the  effects on  ozone  of  changes  in the atmosphere's chemical
composition two approaches are utilized.   First,  measurements of recent
changes in ozone levels  and  other  atmospheric constituents can be compared to
measured  increases  in CFCs and other trace gases.  Second, models can be
developed which attempt  to replicate atmospheric processes affecting ozone
levels.   Moreover,  the first approach can be .used as an important source of
information and validation of the  second.

Ozone Monitoring

    A range of  monitoring using balloons and Umkehr readings show small, but
significant,  decreases of approximately 3 percent in the upper atmosphere  at
mid-latitudes and a 12 percent increase in ozone  (from a smaller base)  in  the
lower troposphere.   Because  of a lack of global distribution of ozone
monitoring equipment, no acceptable method has yet been developed to aggregate
stations  to determine if net change has occurred  on a global basis.  Analysis
using data for the period from 1970-80 suggests,  however, that no significant
net change in total column ozone has occurred.

Model Predictions

     A relatively good consensus exists   among  models  that treat  the world as a
 single column  of air  (one-dimensional models),  and  among  two-dimensional
 models (2-D) that  consider  seasonality  and latitude.  Of  these  model  types,
 2-D models project higher average depletion and show more depletion the
 further  one moves  from  the  equator  (Exhibit 10).
                            *  *  *   DRAFT FINAL  * *

-------
                                                                                               EXHIBIT 10
          Model  Comparison  for  Coupled
          Scenario:    1-D  and  2-0  Model,
                    Global Average
   Two  Dimensional  Model:    CFC  Emissions
           Rolled  Back  to  1980  Levels
Depletion  by  Latitude  for  3% Growth  CFCs
                                                                                                                                              -10
Global average change In total eoluan O>OD«  aa calculated by aeversl
node ling group! (or  a rnaann scenario of:

        Compound      Growth late (X par T««r)

        Clta           1.0 (eeUeelons)
        CB4           1.0 (concentrations)
        N20           0.2>  (concentrations)
        C02          -0.60  (concentrations)

leaulta ahown  (or 2-D eodols of  leaasen  and a£R, I'D etodels o(
Iraaaaur and Vuabbla*,  and Connall'a paraatetarizatlon of  th« LLNL
1-D axxael

toutca:  CheeUcal Haaufacturara  aaaoclatloo. (I in
 growth per year in CFC eeiiaaiooa;  IX growth  io CH4 concent rat ii
 growth in N20 concentratlona. and approxiatately 0.1X growth to i
 concentratlona.  Changes ahown for M)*N.  SO*N. and tO*N.  Teaape
 cooaidered In •odal.

 Source:  laefcaao (peraonal coaaaunteat ion).
    » (or n
    O.liX
C01
irature (aedherfc

-------
                                   -20-
Testing Model  Validity

    As one test of their validity, model predictions can be compared against
current atmospheric observations and historical changes.  These comparisons
show that current models do a relatively good job replicating most
observations, but inconsistencies with some measurements of atmospheric
constituents do occur.  These inconsistencies reduce our confidence in the
predictive capabilities of the current models.

    Comparisons of models against upper stratospheric depletion estimates from
the 1970 to 1980 timeframe show relative consistency (Exhibit 11).

                               EXHIBIT  11

                 Calculated Ozone Depletion for 1970 to 1980
                          vs. Umkehr  Measurements
                                                     nt

                                                    1*43
                                  OCCAOM. OZONICMANOCS
     In  contrast,  comparison  of  model  results  to  the Antarctic ozone hole  and
to the  alleged  Arctic  hole suggest  that  factors  influencing this seasonal loss
of ozone  may  not  be incorporated  in current models  (Exhibit 12).

                                EXHIBIT 12
It
It
14
li
II
1
t
4
2
174
\»
s;

\
x
V
&
yimmm j ••Mint*
l*f.«-l*M


*•

^ r< 2.4 14 *





T-*
KS
1 1
                                        lialm
                           * * *  DRAFT FINAL  * * *

-------
                                   -21-
    Until more information is available concerning the cause  of  the  changes  in
Antarctica, revisions to these models would be unwarranted.   Inadequate
scientific evidence is available to determine whether the phenomenon is a
precursor to future atmospheric behavior or merely an anomaly created by
special geographical conditions unique to Antarctica.

    Scientific analysis of the alleged "Arctic hole" has not  proceeded far
enough to draw any conclusions about whether it is real or temporary, or to
determine its cause.  Consequently, neither phenomenon provides  a basis for
revising model depletion estimates, although they clearly raise  the
possibility of missing chemistry (or aerosols, for example).   Continued
research and analysis could in the future necessitate a revision of  risk
estimates.

Uncertainties in  Laboratory Inputs

    The uncertainties about kinetic rates based on laboratory experiments were
examined in several studies.  This represents one possible area  of
uncertainties in current model configurations.  These studies suggest that
depletion is likely if CFCs grow, and that depletion significantly greater
than predicted in the standard case is more likely than depletion
significantly smaller.

Global Warming

    Global warming  is considered likely as a result of increases in these
trace gases, including vertical reorganization of ozone in the stratosphere
and increased water vapor.  As a benchmark, the magnitude of warming has been
estimated as 3°C +  1.5°C for doubled C02 or the radiative equivalent in other
gases.  The primary source of uncertainty  is the feedback from clouds.  The
timing of this warming is considered uncertain because of delays currently
estimated of 10-40  years due to oceanic heat absorption.  Regional climatic
change cannot yet be  reliably predicted.   Only gross characteristics are
possible such as, increased warming the further one moves toward the poles,
intensified hydrological cycles, and changes in the wetness or dryness of most
of the world's regions.  The global warming predicted  for standard scenarios
is shown  in  (Exhibit  13).

RISKS TO HUMAN  HEALTH

    Because  UV-B varies by  latitude under  current conditions, a natural
experiment exists with more UV-B radiation affecting those living closer to
the equator  than those  located nearer  the  poles.  Based on extensive
laboratory studies  and  epidemiological  analysis, basal  and squamous  skin
cancer have  been demonstrated  to be  related  to UV-B  radiation and can  be
expected  to  increase  with ozone depletion  (Exhibit  14).   Death  is fairly
infrequent for these  cancers'-- about  1% of  cases are  fatal with the
preponderance  of deaths resulting  from squamous  cancers.
                           * * *  DRAFT FINAL  *  * *

-------
                                                                  EXHIBIT 13
                  A 3-D Time Dependent Model  Projection
                   ,   Realized  Temperature Increases
                                                   A 1-D Tine Dependent Model  Projection
                                                         of Equilibrium  Temperature
   Results of Transient Analysis Using a General Circulation Model

H

$

MSI
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set*





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                                                                                                                                                       I
                                                                                                                                                      ro
                                                                                                                                                      to
                                                                                                                                                       i
                                                                                   I9SS
                                                                                         1«9S
                                                                                                3008   JO1S
                                                                                                                   JOiS   2 CMS    3085   1O69
                                                                                                                                             1078
       1960    1970   1980
1990   2000
   DATE
2010   2020    2030
 Exhibit 13

 Only two time-dependent simulations  have been  conducted using a general
 circulation model.   The results,  shown above,  indicate an  increase in global
 average temperature of approximately 0.9°C by  the year 2000  for Scenario A
 (which is a continuation of current  rates of growth  in trace gases).  Scenario
 B (which reflects reduced rates of trace gas growth)  indicates a waiving of
 about 0.5°C by 2000.  Scenario A  achieves a radiative forcing equivalent to
 that of doubled C02 about 40 years from now; Scenario B requires 75 years.
 Temperature equilibrium warming  In this model  is 9°C  for doubled C02.
                                                  * Cooput*d Msunlns that the cliMt* m«n«ltlvity to a doubling of carbon
                                               dioxida i* 3*C.  Thla assumption la in th« aiddl* of th« NAS rang* of l.S'C to
                                               4.5*C (>•• Chaptar 6).  Nota that tha actual waning that m*j b» raallud Mill
                                               lag by aavaral dacada* or •or*.
   Source:   Hansen  198S

-------
                                                                    EXHIBIT  1l»
          Relationship Between 0V and Skin Cancer Incidence
                                                                                Project Percentage Change  in  Incidence of Basal and
                                                                               Squamous Cell Skin Cancers  for  a  Ton Percent Depletion
                                                                                in  Ozone for San Francisco Using DNA Action Spectrum
I!
o  -
C  «


Basal
Male
Female
Squaaoua
Mala
Paula

LOW

21. 15
6.72

33.95
35.3U
Set low ONA
Mid

30.*4l
16.43

51.87
57.93

High

J|0
26.97

f/.. 19
8'4.6»
ro
to
i
' i
I 51 *
• si
i ' i
•* •
: 1
3 i i
5; 1
1 . 1
i 1
° i
1 ;

                           UV ( count*)
2 According to annual UVB measurements  at selected  areas of the  United States

with  regression lines based on an exponential model.


Source: Scotto and Fraumeni (1982).

-------
                                          -24-
     Melanoma  is a more deadly  form of skin cancer and there is  greater
uncertainty attached to  its relationship  to UV-B.  While  there  is not proof
that UV-B causes melanoma, overall the evidence supports  a judgment  that  it is
an  important  contributing factor (Exhibit 15).


                                      EXHIBIT  15


            Information That Has  Been Interpreted As  Supporting the
          Conclusion  that  Solar  Radiation  is One  of Causes  of Cutaneous
                               Malignant  Melanoma (CMM)

               • Vhites have higher CMM incidence and mortality rates than blacks.

               • Light-skinned whites including those who are unable to tan or who tan
                   poorly, get more CMM than darker-skinned whites.

               • Sun exposure leading to sunburn apparently induces melanocytic nevi.

               • Individuals who have more nelanocytic nevi, develop more CMM; the greatest
                   risk  is associated with a particular  type of nevus--the dysplastic nevus.

               • Sunlight induces freckling, and freckling  is an important risk  factor.

               • Incidence has been increasing in cohorts in a manner consistent with
                   changes in patterns of sun exposure,  particularly with respect to
                   increasing intermittent exposure of certain anatomical sites.

               • Immigrants who move  to surjtier climates have higher rates of CMM than
                   populations in their ccuntry of origin and develop rates approaching th^se
                   of the adopted country; this increase in risk is particularly accentuated
                   in  individuals arriving before the age of puberty (10-14 years).

               • CMM  risk is associated with  childhood sunburn; this association may
                   reflect an individual's pigmentary characteristics or may be  related to
                   nevus development.

               • Most studies that have used  latitude as a  surrogate for sunlight or UVB
                   exposure have found an increase  in the incidence or mortality of CMM as
                   one  approaches the equator.

               • Patients with xeroderma pigmentosum who cannot repair CVB-induced  lesions
                   in  skin DNA have a 2000-fold increased risk of CMM by the age of 20.

               • One  form of CMM, Hutchison's melanotic freckle melanoma, appears  almost
                   invariably on the  chronically sun damaged  skin of older people.


           Information That Has  Been  Interpreted As  Not Supporting the
     Conclusion  that  Solar  Radiation  is  One of Causes  of  Cutaneous  Melanoma
                • Some ecologic epidemiology studies have failed to find a latitudinal
                   gradient  for CMM.

                • Outdoor workers generally have  lower incidence and mortality rates  for C>
                   than indoor workers.

                • t'nlike basal cell and sc.anous  cell carcinomas, most CMM occurs  on  sites
                   that are  not habitually exposed  to sunlight.
                                *"*"*•-DRAFT FTflM

-------
                                   -25-
    Laboratory experiments and case studies demonstrate that UV-B can suppress
the immune system in animals and humans.  This response is thought to be a
factor in the development of skin cancer.  In addition, two infectious
diseases, herpes and leishmaniasis, appear to be affected by UV-B, in part,
due to suppression of the immune system.  Other diseases have not been studied.

    Although scientific understanding of the causes of cataracts  is
incomplete, UV-B exposure appears to be one contributing factor to their
development.  Epidemiological studies, animal studies, and biochemical
analysis provide support for linking UV-B and cataracts, though other factors
including exposure to UV-A also play a role (Exhibit  16).

                               EXHIBIT 16

               Estimated Relationship Between  Risk of Cataract
                               and  UV-B Flux
             Ftrccnt
             Increase
             la
             Cataract
             Prevalence
20

18

16

14

12-

ID-

 S'

 6-

 4

 2

 0
                                                         ACE - in
                                                         AGE - 60
AGE • 70
                                 10     15    20    15

                                Percent Increase la UV-B Flux
                                                        30
Although  curable,  cataracts  in the U.S.  still cause one-third of all
blindness.   In  less  developed countries, the health hazards are more severe.

RISKS  TO TERRESTIAL CROPS AND AQUATIC ECOSYSTEMS

     Because  the current species of plants have evolved under existing
radiation conditions,  the question arises as to their ability to grow under
elevated  exposure  to UV-B.   Early studies tested tolerance to UV-B in
greenhouses  and showed substantial susceptibility for many cultivars.
However,  limited experiments under field conditions have demonstrated that to
some extent  a photorepair mechanism reduces damage.
                           * * *  DRAFT FINAL  * * *

-------
                                   -26-
    Soybeans are the crop that has been tested most  extensively.  These  field
studies conducted for a period of over five years  show that  for  a particular
cultivar reductions in yield of up to 25 percent are possible  for a  20 percent
depletion of ozone.

    Field experiments have also demonstrated that  competitive  balances between
planes can be influenced by higher UV-B.  The implications  cannot be
calculated, however, due to the lack of understanding about  current  ecosystem
dynamics and the paucity of field experiments on the subject.

    The use of selective breeding to choose genotypes insensitive to UV-B may
be possible.  However, because the genetic basis for resistance  is not
adequately understood, this mitigation approach remains uncertain.

    Consequently, while evidence indicates that yield from some  cultivars of
crops may be reduced, the magnitude and dimensions are uncertain.

    Based on laboratory experiments aquatic organisms appear to  have low
thresholds to UV-B exposure.  Enhanced UV-B would probably alter the community
composition of phytoplankton, which are at the bottom of the food chain  and
which must remain close to the waters surface to absorb sunlight.   Larvae of
commercially important aquatic organisms also appear subject to  damage  from
enhanced UV-B.  The great uncertainties, however, are the extent of  exposure
to enhanced UV-B in natural conditions  in which water mixing and turbulence
may play a role, and the life cycles of the organisms.  Current  information
suggests a significant risk.  For example, one study showed a 8% anchovy loss
for a 9% depletion.  But current knowledge is insufficient to determine  the
actual dimensions or magnitude of the risk.

RISKS TO POLYMERS

    Ultraviolet-B  radiation harms polymers, causing cracking,  yellowing, and
other effects that  reduce their useful  life.  Stabilizers can be added,  at a
cost, to reduce damage, although  in some cases they may also reduce product
viability.   Increases  in humidity and temperature could exacaberate harm to
polymers.

    Due to a  lack  of experimental data, uncertainty exists about the effects
of UV-B and ozone  depletion on polymers, requiring  approximate estimation
methods to be used.

    Only one  polymer has been analyzed  in  detail  -- polyvinylchloride (PVC).
Based on a single  study, 26% ozone depletion  by 2075 would cause a cumulative
economic damage of 4.7 billion dollars  (undiscounted)  in the U.S.

RISKS  TO TROPOSPHERIC  AIR POLLUTION

    One study recently analyzed  the  effects  of  increased UV-B on the formation
of  ground-based oxidants  (i.e.,  smog).   It showed that in three cities
 increases  in UV-B  could  increase  ground-based ozone (regulated by EPA at 0.12
ppm),  with global  warming excaberating  the situation  (Exhibit 17).  Ground-
based ozone would  also form earlier  on  the day,  exposing  larger numbers  of
people to  peak values.

                          * * *   DRAFT FINAL  * * *

-------
                                    -27-
                                EXHIBIT 17


                  Global Warming Would  Exacerbate Effects of
                       Depletion on  Ground-Based Ozone


                                     Nashville

                                      41.5%
                 17% Depletion
                 and
                 4°C Temperature <
                 Rise             ^
                                      17.7%
              4° C Temperature
              Rise
                                                  17% Depletion
                                                  Only
                           Increase in Ground-Based Ozone


                                    Philadelphia
                                      19.6%
                 17% Depletion
                 and
                 4°C Temperature
                 Rise
                                       6.3%
y///////.
              4° C Temperature
              Rise
                                                  17% Depletion
                                                  Only
                           Increase in Ground-Based Ozone
                 17% Depletion
                 and
                 4° C Temperature
                 Rise
Source:  Whitten and

        Gery  (1986)
                                     Los Angeles

                                       10.4%
                                                  4° C Temperature
                                                  Rise
                                                  17% Depletion
                                                 'Only
                           Increase in Ground-Based Ozone
                               * * *  DRAFT FINAL * * *

-------
                                   -28-
    In addition, a preliminary study indicates  a strong  relationship  between
UV-B and hydrogen peroxide, an oxidant and acid rain precursor.   In Los  Angeles
the effect of 33% depletion was to double hydrogen peroxide;  in  Philadelphia
it would increase by a factor of 16.  These findings need  to  be  verified in
chamber tests.

RISKS FROM  CLIMATE CHANGE

    CFCs and stratospheric modification may contribute as  much as 40-50% of
total predicted global warming in high trace gas growth  cases and 20-30* in
the central case.  Estimates of the effects of  climate change are in  early
stages of research.

Potential  Increases and Effects of Sea Level

    Different studies have analyzed the potential contributions  to sea level
rise from different sources.  Several have made estimates  of  thermal  expansion
due to global warming.  One study has also estimated alpine mountain  runoff
and its contribution to sea level rise, while others have  looked at the
potential contribution from deglaciation.  The estimates are  quite consistent
(Exhibit  18).

                               EXHIBIT 18

                     Estimates of Future Sea Level  Rise
                               (centimeters)

Year 2100 by Cause (Year 2085 for Revelle 1983):
                         Thermal    Alpine
                        Expansion  Glaciers  Greenland  Antarctica
Total
Revelle (1983)
Hoffman et al
Meier et al.
Thomas (1985)
Hoffman et al
. (1983)
(1985) c/

. (1986)
30
28-115
-
-
28-83
12
b/
10-30
-
12-37
12
b/
10-30
-
6-27
2
b/
-10-+100
0-200
12-220
70
56-345
50-200
-
57-368
    a/ Revelle attributes  16  on to other  factors.

    b/ Hoffman et al.  (1983)  assumed that the glacial contribution would be
    one to two times  the contribution of  thermal expansion.

    c/ NAS (1985) estimate includes extrapolation of thermal expansion from
    Revelle (1983).

    Sources:   Hoffman et al.  (1986); Meier et al.  (1985);
              Hoffman et al.  (1983): Revelle  (1983); Thomas  (1985).
                           * * *  DRAFT FINAL  *  *  *

-------
                                   -29-
    Sea level rise can be expected to innundate marshes, erode coastal areas,
increase flooding, and cause saltwater intrusion (Exhibit 19).

    One study estimated that a 100 to 200 cm sea level rise would eliminate 50
to 80% of coastal wetlands depending, in part, on whether new wetlands are
allowed to form or whether developed areas are protected.  Several case
studies have demonstrated that specific recreational beaches would disappear,
unless periodic beach and island nourishment with sand occurred.   Case studies
of Galveston and Charleston indicate that significant economic damage would
occur, particularly from flooding.  These studies also show that  anticipatory
planning can significantly reduce damages.

    Other studies suggest river deltas are particularly at risk from sea level
rise.  Much of the Mississippi delta is already expected to disappear over
time due to subsidence; sea level rise would accelerate this problem.  In
Bangladesh and Egypt, one study estimated that subsidence and global sea level
rise could cause displacement of 16-21 percent of Egypt's population and 9-21
percent of the population of Bangladesh.

Possible Effects on  Forests

    Climate models predict that a global warming of approximately 1.5°C to
4.5°C will be induced by a doubling of atmospheric C02 or equivalent radiative
increases from other trace gases.  This C02 doubling or  its equivalent is
likely to take place during the next 50 to 100 years.  The period 18,000 to 0
years B.P. is one possible analog for a global climate change of this
magnitude.  The geological record from this glacial to inter- glacial interval
provides a basis for qualitatively understanding how vegetation may change in
response to large climatic change, though historically this occurred over a
much  longer time period.

    The paleovegetational record shows that climatic change as large as that
expected to occur in response to a C02-doubling is likely to  induce
significant changes  in the composition and patterns of the world's biomes.
Changes of 2°C to 4°C have been significant enough to alter the composition of
biomes, and to cause new biomes to appear and others to  disappear.  At 18,000
B.P., the vegetation in Eastern North America was quite  distinct  from that of
the present day.  The cold/dry climate of that time seems to  have precluded
the widespread growth of birch, hemlock, beech, alder, hornbeam,  ash, elm and
chestnut, all o2 which are  fairly abundant in present-day deciduous  forest.
Southern pines were limited to Florida along with oak and hickory.

    Limited experiments  conducted with dynamic vegetation models  for North
America suggest that decreases in net biomass may occur  and that  significant
changes in species  composition are likely.  Experiments  with  one  model suggest
that  Eastern North  American biomass  may be reduced by 11 megagrams per hectare
 (10%  of live biomass) given the  equivalent of a doubled  C02 environment.
Plant taxa will respond  individually rather than as whole communities to
regional  changes  in climate variables.  At this time  such analyses must be
treated as only  suggestive  of the kinds of change that  could  occur.   Many
critical  processes  are  simplified or omitted  and the  actual situation  could be
worse or  better.
                           * * *  DRAFT FINAL  * * *

-------
Evolution  of March as  Sea  Level  Rises
                                                                                    EXHIBIT  19

                                                                                       Erosion;  The  Bruun  Rule
                                                                                     Saltwater  Intrusion
  5000 Yean Ago
                                                  Today
                 -••• I**    $•»<"•"«
                         Future
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Co»t«l •*c*b«» h»v« k«pt p«c« with tb« •lot
•>p«Bd*d ov«r tiM •• aw land* war* inuftdfi
rlttt f«it»r than tba ability of tba aarsh i
contract. Coaacmctlon of faulUiaad* to proi
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t*d. If lo tba futur*. ••• laval
to kaap paca, tba aartb araa will
tact acoooaiic davalapaiat Mf
* tu« to !•• l»v»l of I c*tt««» liw^l«t
•*••!»•! ly t*^ult* th« offihor* bottaa t
would b* tuppllMd fro* tb« up»«r y*rt o
f It «qu«l to I * p/(h*4)
                                                                                                  o tU« by >.  Th* a«c«*««ty S utd »'
                                                                                                  ito b««cb A,  Total •tor«lin« r*t*»i
                                                                                                                                                                IM •« CI/I
Percent of tid*l cjrcUs  In which •p*clft*4 concMtrat io* is vac***** at
Torr*td«U during • r«curr«nc* of th« 1**0'« drou«ht for thr*« ••• l«v«l
tc*narloi   TTi* 210 «| CI/I U>-«l U ch« EPA drinking w«t*r 
-------
                                   -31-
Possible  Effects on Crops

    Climate has had a significant impact on farm productivity and geographical
distribution of crops.  Examples include the 1983 drought which contributed to
a nearly 30% reduction in corn yields in the U.S., the persistent Great Plains
drought between 1932-1937 which contributed to nearly 200,000 farm
bankruptcies, and the climate shift of the Little Ice Age (1500-1800) which
led to the abandonment of agricultural settlements in Scotland and Norway.

    The main effects likely to occur at the field level will be physical
impacts of changes in thermal regimes, water conditions, and pest
infestations.  High temperatures have caused direct damage to crops such as
wheat and corn; moisture stress, often associated with elevated temperatures,
is harmful to corn, soybean and wheat during flowering and grain fill; and
increased pests are associated with higher, more favorable temperatures.

    Even relatively small increases in the mean temperature can increase the
probability of harmful effects in some regions.  Analysis of historical data
has shown that an increase of 1.7°C (3°F) in mean temperature changes the
likelihood of a five consecutive daily maximum temperature event of at least
35°C (95°F) by about a factor of three for a city like Des Moines.  In regions
where crops are grown close to their maximum tolerance limits, changes in
extreme temperature events may have significant harmful effects on crop growth
and yield.

    Current projections of the effects of climate change on agriculture are
limited because of uncertainties in predicting local temperature and
precipitation patterns using global climate models, and because of the need
for improved research studies using controlled atmospheres, statistical
regression models, dynamic crop models and integrated modeling approaches.

    Higher ambient C02 levels may enhance plant growth, decrease water use,
and thereby  increase crop yield and alter competitive balances in ecosystems.
These factors must be evaluated in conjunction with changes in climate
regimes.  Large uncertainties exist because few  long-term and multiple stress
studies have been completed.

Possible Effects on Water Resources

    There is evidence that climate change since  the last ice age  (18,000  years
B.P.) has significantly altered the  location of  lakes although the extent  of
present  day  lakes  is broadly  comparable  with  18,000 years B.P.  For  example,
there  is  evidence  indicating  the existence of  many tropical  lakes and swamps
in the Sahara, Arabian, and Thor Deserts around  9,000 to 8,000 years  B.P.

    The  inextricable  linkages between the water  cycle and climate ensure  that
future climate change will significantly alter hydrological processes
throughout the world.  All natural hydrological  processes -- precipitation,
infiltration,  storage and movement of soil moisture,  surface and  subsurface
runoff,  recharge of groundwater, and evapotranspiration  -- will be affected
                           * * *  DRAFT FINAL  * *

-------
                                   -32-
be affected if climate changes.  Until models of regional climate change are
improved, it will be difficult to obtain an understanding of the risks
associated with gloal warming.

Possible Effects on  Human  Health

    Weather has a profound effect on human health and well being.  It has been
demonstrated that weather impacts are associated with changes in birth rates,
outbreaks of pneumonia, influenza, and bronchitis, and related to other
morbidity effects and linked to pollen concentrations and high pollution
levels.

    Large increases in mortality have occurred during previous heat and cold
waves.  It is estimated that 1,327 fatalities occurred in the United States as
a result of the 1980 heat wave and Missouri alone accounted for over 25% of
that total.

    Hot weather extremes appear to have a more substantial impact on mortality
than cold wave episodes.  Most research indicates that mortality during
extreme heat events varies with age, sex, and race.  Acclimatization may
moderate the impact of successive heat waves over the short-term.

    Threshold temperatures for cities have been determined which represent
maximum and minimum temperatures associated with increases in total
mortality.  These threshold temperatures vary regionally, i.e., the threshold
temperature for winter mortality in mild southern cities such as Atlanta is
0°C and for more northerly cities such as Philadelphia, the threshold
temperature is -5°C.  Humidity and precipitation also have an important impact
on mortality, since it contributes to the body's ability to cool itself by
evaporation of perspiration.

    If  future global warming  induced by increased concentrations of trace
gases does occur, it has the potential to significantly affect human
mortality.  In one  study,  total summertime mortality in New York City was
estimated to increase by over  3,200 deaths per year for a 7°F trace
gas-induced warming without acclimatization.  If New Yorkers fully
acclimatize, the number of additional deaths is estimated to be no different
than  today.  It is  hypothesized that, if climate warming occurs, some
additional deaths are  likely  to occur because economic conditions and the
basic infrastructure of the city will prohibit  full acclimatization even if
behavior changes.
                           * * *  DRAFT FINAL  * * *

-------
                                   -33-
AN INTEGRATED ANALYSIS OF RISKS OF STRATOSPHERIC MODIFICATION

    In order to assess risks from stratospheric modification in  the  absence of any
future regulatory action, the various assumptions (e.g.,  trace gas growth,
atmospheric response, incidence of skin cancer, etc.) have to be linked  in  an
integrated modelling framework.  Since significant uncertainty exists  about each
component, a central case was estimated along with alternative assumptions.1
    1 The central case estimates reflect the most likely values  of key
assumptions and inputs used to model risks:

•   Annual production of CFC 11 and 12 grow at an annual average rate of  2.5
    percent from 1985 to 2050, and remains constant following 2050; growth  rates
    for other chlorine and bromine substances as described in Chapter 3.  The
    compounds analyzed include:  CFC-11, CFC-12, CFC-22, CFC-113, methyl
    chloroform, carbon tetrachloride, Halon-1211, and Halon-1301.  Emissions
    estimates reflect the storage of some substances in their end-use products  for
    many years.

•   Consensus estimates of the annual rates of increases in atmospheric
    concentrations of other trace gases are used:  carbon dioxide (C02) at  0.6
    percent; methane (CH4) at 1.0 percent; and nitrous oxide (N20) at 0.25
    percent.  Trace gas assumptions are discussed in Chapter 4.

•   A parameterized relationship between emissions of ozone modifiers, trace  gas
    concentrations and global ozone depletion is used.  This equation reflects  the
    results of a one-dimensional model of the atmosphere using the most recent
    estimates of reaction rates.  The parameterized atmospheric model (described
    in Chapter 17) was derived from the LLNL Model developed by Wuebbles  (reported
    in Chapter 5).

•   The  latitudinal distribution of ozone depletion is evaluated using the
    results of a time-dependent two-dimensional model of the atmosphere.  The
    latitudinal analysis of ozone depletion is presented in Chapter 17.

•   The  relationship between changes in ozone abundance and changes in UV flux
    reaching the earth's surface is based on estimates of a radiation model of  the
    atmosphere.  The estimates of UV flux are described in Chapter 17.

•   The  risks to human health due to increases  in UV are evaluated using middle
    estimates of dose-response coefficients developed in epidemiologic analyses in
    the  U.S.  The quantifiable risks to human health are described in Chapters  7,
    8, and  10.

•   The  middle estimate by  the National Academy  of Sciences  (NAS)  for the
    sensitivity of the global  climate to greenhouse gas forcings  is used -- 3.0°C
    equilibrium warming for a  doubling of  the concentration of  C02.  The National
    Academy of Sciences estimates are presented  in Chapter 6.   Recent analyses  of
    climate sensitivity indicate that a 4°C sensitivity may be  a preferred central
    case assumption  (Manabe and Wetherald  1986;  Washington and  Meehl  1984;  Hansen
    et al.  1984).
                           * * *  DRAFT FINAL  * *  *

-------
                                   -34-
    Exhibit 20 shows predicted depletion for a range of cases with varying
assumptions about trace gas growth.

                               EXHIBIT 20

             Global Average  Ozone Depletion:  Emission Scenarios
                          (LLNL 1-D Model  Results)
   2
   u
   O
   N
   0
       -10 -
       -15 -
        -20 -
        -25 -
        -30
          1935
                    2005
                             2025
                                       2045
                                                 2065
                                                          2085
Key Assumptions:

Common to Each Scenario

•   CH4 concentrations:  1% per year
•   C02 concentrations:  0.6% per year
•   N20 concentrations:  0.25% per year

Varying in  Each  Scenario

Annual Growth in CFC-11 and CFC-12 production
                   (%/year)
           Lowest
           Low
           Central
           High
           Highest
0.0
1.2
2.5
3.8
5.0
 Other CFCs,  and chlorinated  and  brominated compounds
 also growing.
                           *  * *   DRAFT FINAL  * * *

-------
                                   -35-
    Exhibit 21 shows predicted health  effects  in the U.S for the central case
assumptions.

                               EXHIBIT 21

                     Human Health Effects:  Central Case
       (Additional Cumulative Cases and Deaths by Population  Cohort)
       HEALTH EFFECT
 POPULATION

ALIVE TODAY
                                        a
      NUMBERS

BORN 1985-2029*
        NUMBERS

BORN 2030-2074°
Non-Melanoma Skin Tumors
Additional Basal Cases
Additional Squmaous Cases
Additional Deaths
Melanoma Skin Tumors
Additional Cases
Additional Deaths
Senile Cataract
Additional Cases

630,600
386,900
16,500

12,300
3,900

593,600

5,012,900
3,185,800
135,000

109,800
32,200

3,463,400

17,630,500
12,122,400
509,300

430,500
115,100

8,295,800
   Analysis period for health effects:  1985-2074.

   Analysis period for health effects:  1985-2118.

   Analysis period for health effects:  2030-2164.
     Exhibit  22 presents  limited evidence from case studies for other key
 effects  based on  the central case assumptions.

 Sensitivity to Assumptions About Greenhouse  Gases that Counter Depletion

     The  above case  assumes unconstrained greenhouse gas growth.  Exhibit 23
 examines an  alternative  set of assumptions which consider the possibility that
 future actions might be  taken by governments to limit climate change.
                           * *  *   DRAFT FINAL  * * *

-------
                             -36-
                         EXHIBIT 22

      Materials, Climate and Other Effects:   Central Case



     TYPE OF EFFECT                 EFFECT           UNITS


Effects Estimated Quantitatively for the U.S.

   Materials Damage a/                550      Present Value
                                               (millions of 1985
                                               dollars)

   Rise in Equilibrium                6.2      Degrees Centigrade
   Temperature by 2075 b/

   Sea Level Rise by 2075             101      Centimeters

Effects Based on Case Studies and Research in Early Stages

   Cost of Sea Level Rise         1,145-2,807  Present Value
   in Charleston and Galveston c/              (millions of 1985
                                               dollars)

   Reduction in Soybean Seed         14.3      Percent in Year 2075
   Yield d/

   Increase in Ground-Based       5.1-27.2     Percent in Year 2075
   Ozone e/

   Loss of Northern Anchovy       3.8-19.8     Percent in Year 2075
   Population f/

a/  Discounted over 1985-2075 using a real discount rate of 3
    percent.

b/  Estimated using an assumed climate  sensitivity of  3°C  (middle
    NAS estimate).  Recent analysis indicates that 4°C may be a
    preferred central case assumption.   Using a 4°C sensitivity, the
    estimated equilibrium warming in 2075  is about 8.4°C.

c/  Lowest  estimate with anticipation of sea level rise; highest
    estimate without  anticipation.

d/  Essex cultivar only  in years of average  current climate.

e/  Lowest  estimate is for Los Angeles, California; highest
    estimate  is  for Nashville, Tennessee.

f/  Lowest  estimate assumes  15-meter vertical mixing  of  the top
    ocean layer; highest estimate  assumes 10-meter vertical mixing.

                    * *  *  DRAFT FINAL   * *  *

-------
                                   •37-
                               EXHIBIT 23

             Global Average Ozone Depletion:  Scenario of Limits
                          to Future Global Warming
    2
    u

    0
    M
    0
           19S5
                    2005
                              2025
                                        2045
                                                 2065
                                                           2035
It shows the effects of ozone depletion if steps were taken to limit  growth as
trace gas emissions to the level of greenhouse warming of 3°C.   By limiting
the buffering of ozone depletion by the growth in these greenhouse gases,  the
negative effects of CFCs and halons on ozone in the stratosphere is increased.

    Exhibits 24 and 25 show the effects on health effects and other factors
for the same assumptions of limited greenhouse gas growth.

Comparison of One-Dimensional Model to a Two-Dimensional Model

    The estimates given above are derived from the one-dimensional model used
throughout this review.  Comparison of these global ozone depletion estimates
to those from a two-dimensional model, indicate that it produces levels of
ozone depletion slightly less than half of those by a two-dimensional model
(Exhibit 26).
                          * * *  DRAFT FINAL  * * *

-------
                           -38-
                         EXHIBIT 24

Cumulative Health Effects for  People  in U.S.  Alive Today and
    Born  in Next 88  Years With Greenhouse Gases Limited
       HEALTH EFFECT
LIMITS TO FUTURE GLOBAL WARMING
            *    Central Case
 3°C + 1.5°C      (no limit)
Non-Melanoma Skin Tumors

  Additional Basal Cases         50,984,500       23,274,000

  Additional Squamous Cases      41,814,400       15,695,100

  Additional Deaths               1,726,000          660,800

Melanoma Skin Tumors

  Additional Cases                1,137,600          552,600

  Additional Deaths                 308,500          151,200

Senile Cataract

  Additional Cases               22,817,600       12,352,800
  * Uncertain of +1.5°C due to uncertainty about true sensi-
 tivity of earth to radiative forcing (e.g., same greenhouse gas
 increase).
                   * *  *   DRAFT FINAL  * * *

-------
                                        -39-
                                    EXHIBIT 25

            Materials,  Climate,  and Other  Effects:   Scenarios of  Limits
                              to Future Global  Warming
       (Figures  in Parentheses are Percentage  Changes from Central  Case)
      TYPE OF EFFECT
                              LIMITS TO FUTURE GLOBAL WARMING
                                    3 C      Central Case
                                              (no  limit)
                                                                     UNITS
Effects Estimated  Quantitativetv for the U.S.

   Materials Damage a/             726           550
   Ri se in EquiIibrium
   Temperature by 2075

   Sea LeveI  R i se by 2075
                                  3.0
                                 (-52)
                                   76
                                 (-25)
Effects Based on Case
Studies and Research  in Early Stages
   Cost of Sea Level  Rise  in
   Charleston and Calveston b/
   Reduction in Soybean Seed
   Yield c/

   Increase in Ground-Based
   Ozone d/

   Loss of Northern Anchovy
   Population §/
                                967-2328
   6.2


   101




11U5-2807
                                 >19.0       1U.3


                               >9.U->50.0    5.1-27.2


                               >11.0->25.0   3.8-19.8
Present  Value
(millions of  1985 dollars)

Degrees  Centigrade


Centineters
Present Value
(mill ions of  1985
dol lars)

Percent in Year 2075
              Percent in Year 2075
              Percent in Year 2075
a/ Discounted over 1985-2075 using a real discount rate  of  3  percent.

b/ Lowest estimate with anticipation of sea level  rise;  highest estimate without
   anticipation.

c/ Essex cultivar only in  normal years.

d/ Lowest estimate is  for  Los Angeles, California; highest  estimate  is for Nashville,
   Tennessee.

e/ Lowest estimate 15-meter vertical mixing of the top ocean  layer; highest estimate
   10-meter vertical Mixing.
                              * *  *  DRAFT FINAL  * * *

-------
                                   -40-
                               EXHIBIT 26

               Global Average Ozone Depletion:  Comparison to
               Results  with  a  2-Dimensional Atmospheric Model
                                                         1-0 3 Permit
                                                         Emissions
                1985
                         IMS
                                   2005
                                             2015
                                                       202S
Sensitivity to Rate of CFC Growth

     As shown in Exhibit 20,  the amount of ozone depletion  is  sensitive  to  the
assumption about future growth of CFCs and other trace gases  (Exhibit  23).
Assuming that other gases continue to increase,  Exhibit  27  shows  the impact on
human health for different CFC growth scenarios.

Uncertainty About Health Dose-Repose Relationships

     Uncertainty exists about the appropriate dose-response relationship for
each of the human health effects.  Exhibit 28 shows an analysis of  the
statistical uncertainty for each of thes areas.

OVERALL ASSESSMENT OF UNCERTAINTY

     The largest quantitative uncertainties involve assumptions concerning
future emissions of CFCs; future greenhouse gas  growth;  the use of  2-D models
for predicting depletion, and uncertainties about dose-response parameters.
Qualitatively the uncertainties for effects include implications  of increased
immune suppression; dose-response relationships  for aquatics,  crops,
terrestial ecosystems; and a vary of climate impacts.  With respect to
modeling the atmospheric consequences of trace gas growth,  there  exists the
possibility that some overlooked or missing factor or oversimplified process
has lead to under- or over-predictions of changes in ozone.
                          * * *  DRAFT FINAL  * * *

-------
                                      -41-
                                   EXHIBIT  27

                      Human Health Effects:  Emissions Scenarios
      Additional Cumulative  Cases and Deaths Over Lifetimes of People Alive Today
            (Figures in  Parentheses  are Percent Changes  from Central Case)
                                   EMISSIONS SCENARIOS              EXTREME CASES
       HEALTH EFFECT            Low      Central       High       Lowest       Highest



Non-Melanoma Skin Tumors

  Additional Basal Cases     1,599,500   23,274,000  83,755,700   -1,616,100  135,317,800

  Additional Squamous Cases    823,400   15,695,100  71,808,100     -856,600  117,809,800

  Additional Deaths             35,700      660,800   2,952,400      -36,700    4,837,400

Melanoma Skin Tumors

  Additional Cases              47,300      552,600   1,897,400      -40,500    3,079,500

  Additional Deaths             12,100      151,200     502,800      -11,200      809,700

Senile Cataract

  Additional Cases             885,000   12,352,800  34,226,900   -1,112,100   53,429,800
                                * *  DRAFT FINAL  * * *

-------
                            -42-
                        EXHIBIT 28

Human Health  Effects:  Sensitivity to  Dose-Response Relationship
 Additional Cumulative Cases and Deaths Over Lifetimes of People
         in U.S.   Alive Today and Born in  Next 88 Years
                                 SENSITIVITY OF EFFECT TO UV DOSE
     HEALTH EFFECT               Low          Central          High
Non-Melanoma Skin Tumors
Additional Basal Cases
Additional Squamous Cases
Additional Deaths
Melanoma Skin Tumors
Additional Cases
Additional Deaths
Senile Cataract
Additional Cases

14,046,400
9,242,000
109,200

384,300
134,300

6,600,200

23,274,000
15,695,100
660,800

552,600
151,200

12,352,800

34,130,500
24,385,300
10,203,000

732,100
168,500

17,038,300
                    * * *  DRAFT FINAL * * *

-------
*"    ^ \        UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
     Dear  Collegue:

          Enclosed is  a  copy of  the  draft document  you requested
    entitled,   An  Asj5es,j>raent.  of_  the Ri..s.ks_ of.  St.jra£os_p_he]:.ic_
     Modification prepared  by the  Strategic Studies Staff of the U.S.
     EPA.   This document  was submitted to the Science  Advisory  Board
     on October 23,1986.   On November 24 and  25  the Science Advisory
     Board, chaired by Dr. Margaret Kripke will meet to review the
     document.

          The  review  process  of  this document follows the traditional
     procedure  used by  the Science Advisory Board.  This includes:

          - Public notice of  the Subcommittee's November 24-25 meeting
     in the  Federal  Register  (in  order to  conform to  the   legal
     requirements of  the  Federal Advisory Committee  Act).

          - Opportunity for succinct technical  presentations  to the
     Subcommittee by  interested  members of  the public  (the  total
     amount of time allotted for  such comments will  not  exceed one
     hour)

          - A  copy  of the  risk assessment  document  and comments
     received  will be available for review  at the Public Information
     Reference Unit,  (202) 382-5926, EPA Headquarters Library, 401 M
     St, SW Washington,  DC between the hours of 8:00  am and 4:30pm.
     The public docket number is A-86-18.


         - When the  SAB Subcommittee meets in November, there will  be
     an exchange of  scientific views between the  Committee  and the EPA
     staff. This informal exchange of  views will cover any questions
     concerning the  validity  of  the scientific assumptions, as well as
     the methodologies and conclusions  of the assessment document.
     The Subcommittee will then develop a consensus  position paper and
     a final report will be  prepared.   Following the finalization  of
     the text, the report will  be sent to the Science  Advisory Board
     Executive Committee  and then directly to the  EPA Administrator.
     EPA will then have time to respond to the Subcommittee's report.

          Written comments should  be addressed to John S.  Hoffman,  at
     PM 220, U.S. EPA, 401 M St,SW , Washington, DC 20460.  Comments
     are due to  the SAB  by November 14.  The public comment  period
     will be open until December 10.

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GLOBAL MODELING OF THE ULTRAVIOLET SOLAR FLUX INCIDENT ON




                      THE BIOSPHERE
                    George N. Serafino



               Applied Research Corporation




                   8201 Corporate Drive



                 Landover, Maryland 20785








                           and








                    John E. Frederick



          Department of the Geophysical Sciences



                The University of Chicago



                 5734 South Ellis Avenue




                 Chicago,  Illinois 60637

-------
                          Abstract



     Thi* report Summarizes an algorithm designed to




estimate the ultraviolet solar flux that reaches the Earth's




surface at any location on the globe and time of year.




Inputs consist of global ozone abundances, terrain height»




the distribution of cloudcover, and the albedos of clouds



and the underlying surface.  Intended users of the algorithm




include atmospheric scientists* the photobiology community,




and environmental policymakers.

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I.  Introduction




     The interaction of solar radiation with  the Earth  and




it* atmosphere is closely coupled to the planet's ability to




support life.  Ultraviolet solar radiation likely initiated




the chemical processes which led to formation of the first



organic molecules on the primitive Earth (eg. Ponnamperuma»




1981)i  while the development of a substantial ozone layer



created a surface environment where complex self-replicating




molecules could evolve.  The decreases shown by both the



absorption cross section of ozone and the DNA action




spectrum at wavelengths between 280 and 320 nm provide




persuasive evidence of the coupling that has existed between




the geophysical and biological realms which ultimately



provided for the evolution of higher life forms.



     Issues of more immediate practical concern center on




the observation that the incidence of various skin cancers



shows  latitudinal variations.  This appears related to the




biologically active ultraviolet flux reaching the surface of




the Earth.  While this fact alone is of great significance*



couplings of a more subtle nature apparently exist between




the radiation environment and biological systems.  A prime



example is  the work by DeFabo and Noonan (1983) which




indicates a  link between ultraviolet radiation dosage and



suppression of the  immune system  in  laboratory mice.



Photobiologists have adopted  the  term UV-A to refer to



radiation over the  wavelength range  320-^00  nm, while UV-B

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denotes the region 280-320 nm.   Absorption  by  ozone  and




atmospheric scattering reduce the solar  UV-B flux  at the




surface of the Earth to a small  fraction of what  Mould




otherwise exist.  The UV-A, being outside the  range  of




strong absorption by ozone* experiences  much  less




attenuation.




     This report describes the conceptual formulation of  an



algorithm designed to predict the UV-B and  UV-A radiation



fluxes as functions of wavelength at any point on the Earth



for any time of year.  Papers which summarize  the




mathematical methods used in the code already  exist  in the




published literature.  We make reference to these rather




than presenting details here.  The algorithm utilizes global




scale ozone measurements obtained by the Solar Backscatterea



Ultraviolet (SBUV) Spectral Radiometer carried on the Nimbus




7 satellite.  Ue combine this data set with additional



information on cloudcover and cloud transmission obtained




from independent sources.  While the development of the



algorithm is an exercise in radiative transfer and




atmospheric science* we  intend the final product to be a



tool for use by the photobiology community and environmental



policymakers.

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II. The Radiative Transfer  Formulation




     We divide the atmosphere into two parts*  (1)  the  clear



atmosphere above any cloudtops and (S) the  cloud  layer»  the



atmosphere beneath the cloud (the "sub-cloud  layer"),  and




the ground.  In the absence of clouds only  case  1  is




required.   When clouds are  present Me merge a  model of this




portion of the atmosphere onto the base of  the clear  sky



calculation.  We assume that the lower boundary  of the clear




atmosphere> being cloudtops or ground* is a Lambertian



surface of known albedo. A radiative transfer calculation




which includes all orders of multiple scattering and




absorption by ozone then gives the direct and  diffuse




components of solar flux incident on the cloudtops or, for




clear skies* on the ground.



     The downward diffuse flux, F (> ,6»T>, for  a wavelength




% » solar zenith angle 6* and optical depth T» can be




expressed as the sum of an  atmospheric scattering component



FC  - R / C1-RS(A »T->]                (2)

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Here T» i« the atmospheric  optical  depth  above the




reflecting surface (ground  or  cloudtop) of  albedo  R»




S< A »T"> represent* the backseattering  power  of the




atmosphere* and F (A »6,T)  measures the contribution  from




flux that has already reflected from the  lower boundary and




is then scattered back into the lower hemisphere.   The



advantage of the formulation in equations 1 and 2  is  that




the quantities FQ * F, » and S can be computed without



knowledge of the surface albedo.   In practice* we  calculate



these terms using the Herman and Browning (1965) clear sky,




multiple Rayleigh scattering model.




     For clear sky conditions the formulation summarized




above produces the UV-B and UV-A flux at  the ground as a



function of wavelength* solar zenith angle (local  time)* and




ozone amount.  Under cloudy sky conditions* however*  we must




define  the transmission and reflectivity of the cloud-



subcloud-ground  layer.  For this we use a two stream




radiative  transfer model coupled with the "adding method"



for a multi-layer atmosphere developed by Lacis and Hansen



(1974).  This approach divides the atmosphere into a series




of homogeneous layers where each layer has a  known



reflectivity and  transmission.  Clouds occupy the uppermost




layers* while the bottom layer is  the ground  with a



transmission of  zero.  The composite reflectivity and




transmission of  the multilayer system  is determined by



combining  the reflectivities and transmissions  of the



individual  layers with proper account  taken of  multiple

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reflection* of upward and downward directed  fluxes.   Lac is




and Hansen <197*»>  have presented quantitative  details of  the



technique.  The model adopts fractional  cloudcover  as a




function of latitude from Hughes (198<*>.   We assume a



mixture of thick low clouds* with an optical depth  for




scattering of 30*  and middle level clouds of optical depth



15 (Stephens* 1978).  We assume cloud drops  to be non-



absorbing in the UV-B and UV-A.  However, absorption of




radiation still occurs in the clouds owing to  the




tropospheric ozone amount included in the model.  The



calculations assume that 85 percent of the downward




radiation incident at the cloudtops is scattered into the




lower hemisphere.   The derived transmission of the cloud-




subcloud system multiplied by the total (direct plus



diffuse) flux incident on the cloudtops from equation 1




gives the flux at the ground.  Note that Me assume all




radiation transmitted through the cloud to be isotropic over




the lower hemisphere* consistent with a large optical depth




for scattering.



     The reflectivity and transmission of atmospheric layers



beneath the cloud deck are defined by expressions for a two




stream model as given by Coakley and Chylek (1975) and



Joseph et al.  (1976).  Each  layer ha* a known optical depth



and an ozone amount based on climatology supplied with the




SBUV data set.  To obtain the flux at the ground for  a



c1imatological fractional cloudcover* we simply combine



values derived separately for clear and cloudy  skies  using

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                                                            e






the weights 1-f and f respectively*  where  f  is  the




fractional cloudcover at the latitude of  interest.




     In principle on* could compute  the UV-B and UV-A fluxes



at the gro.und using a complete radiative  transfer




calculation for any combination of wavelength,  ozone




abundancet cloudcover* solar zenith  angle* and  ground



reflectivity.  In practice this is not necessary.  Instead




we generated three sets of flux tables* one with the base of



the clear atmosphere at 10OO mb* another  at 700 mb>  and the



last with the base at 400 mb.  Each table contains the




radiative transfer quantities of equations 1 and 2 for S3




wavelength bands which span the wavelength range 290 to 400




nm, 9 total column ozone amounts* and  13  solar  zenith




angles.  Surface reflectivities corresponding to the ground



or cloudtops need not enter the tables in view of the form




of equation 1.  Each table allows interpolation to obtain



surface fluxes for any ozone value and local time* while a



combination of all three tables provides  fluxes for varying



terrain heights and cloudcover conditions.  This flexibility




allows the algorithm to predict the ultraviolet radiation



environment at any location on the globe for any  time of



year by interpolation based on precomputed radiation tables.



Surface fluxes may refer to specific  local times  or  to



averages over  the daylight period at  any  location and date.

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III. The Input Data Sett




     The SBUV instrument provides the total  column ozone  and



vertical ozone profiles needed to evaluate terms in the




radiative transfer calculations.   We use SBUV column ozone




amounts averaged over one month time intervals and over all




longitudes in 10 degree wide latitude bands.  We associate



these means with the center of each month and latitude bin.




Interpolation in latitude and time then provides the ozone



amount for a specific location and day of the year.  Figure



1 illustrates the behavior of column ozone as a function of




latitude and month derived from SBUV.  We note that a very



recent revision in the SBUV data set uses improved




absorption cross sections and yields values approximately 6'/<




greater than those shown in Figure 1.  The current version




of  the global radiation algorithm uses the updated ozone




results.  The extraterrestrial solar irradiance. ozone



absorption cross sections, and Rayleigh scattering cross




sections used in the calculations are from Chapter 7 of



WHO/NASA (1986).

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                                                            10
IV.  Algorithm Operation and Sample Results




     The algorithm allows the user a high  degree of




flexibility in selecting parameters for a  given calculation.




Mandatory input* supplied by the user arei (1)  latitude and




longitude* (S) day number of the year, 1 through 365,  and




(3) local time.  As an alternative to local time the user



can choose to compute mean fluxes over the daylight portion




of a 5
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                                                            11
largest fluxes* <» watts per square meter,  reach  the ground




in the tropic* because the sun is most  nearly  overhead here*




•nd the atmospheric ozone Amounts are relatively small.  The



major feature of Figure 2 is the large variation in




radiation flux with latitude* especially  during  the winter




season.  In the Northern Hemisphere for December and January



the flux decreases by a factor of 10 between the equator and




50 degrees latitude.  During summer the latitudinal



gradients are much less pronounced than in winter, and one




must move from the tropics to 60 degrees to experience a




factor of two decrease in flux at the ground.   There is very




little change  in the 10:00 A.M. fluxes in the tropics over




the course of a year.  At middle latitudes* however* the



seasonal cycle can .range between a factor of two and ten



depending on  location.




     A calculation analogous to that in Figure 2 could be



done for the UV-A spectral region.  Although the contours




would be similar in shape* the gradients would be much less




pronounced because of the greatly reduced absorption by



ozone at wavelengths longward of 320 nm.  Figure 3




illustrates this behavior by giving contours of the ratio of



UV-B to UV-A  fluxes as a function of latitude and month at a



local time of  10:00 A.M.  Clearly* the UV-B flux  is much



smaller than  the UV-A* with  the ratio ranging from 2 to



7.SVC.  The most significant  information  in Figure 3 is the



differing latitudinal and  seasonal gradients shown by  the



UV-B and UV-A.  As one moves from the  tropics to  60 degrees

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latitude in winter,  the  UV-B  flux  decreases more  rapidly




than the UV-A by a factor  of  three to  four.   In summer  the



relative variation it much less  than a factor  of  two.




     The example* presented above  illustrate latitudinal  and



seasonal variations.   Future  updates of the algorithm  for




use in truly global  studies should include longitudinal



variations in both fractional cloudcover and ozone. Par




many applications* however* the  focus is on the radiation



environment at a specific  location as well as on  changes  in



dose rates with parameters such  as the ozone amount and




fractional cloudcover.  A  separate report by H. Pitcher and




J. Scotto now in preparation  will  describe such studies*



including the comparison of model  predictions with ground-




based measurements from Robertson-Berger meters.

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                                                            13
                         Reference*



Coakley, J. A., Jr.i  and P. Chylek, 1973:  The two-stream




approximation in radiative transfer! Including the angle of




incident radiation*  J. A_tmp_». Sc_i_. » 32, 409-418.








Dave* J. V.» and P.  M. Furukawa, 1966: Scattered Radiation



in the Ozone Absorption Bands at Selected Levels o_f_ a




Terrestrial Ravleiqh Atmosphere, Meteor. Monogr . , Vol. 7,



No. 29.








DeFabo» E. C., and F. M. Noonan, 1983: Mechanism of immune




suppression by ultraviolet radiation in vivo  I. Evidence



for the existence of a unique photoreceptor in skin and  its




role in photoimmunnology» J. E*p.  Med. > 15?» 8<»-98.








Herman. B. M., and S. R. Browning,  1965: A numerical



solution to the equation of radiative  transfer» J. Atmos.




Sci.. 22, 559-566.








Hughes, N. A., 1984: Global cloud  climatologies: A



historical review, J. Climate Appl. Meteor., 23, 724-751.








Joseph, J. H., W. J. Wiscombe, and J.  A. Weinman,  1976:  The



delta-Eddington approximation for  radiative flux  transfer,




J. Atmos. Sci.. 33,  175-204.

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Kalnay, E., et al., 1983: Documentation o_f  the GLAS Fourth




Order GDI.  Vo1ume li Model Documentation,  internal report,




Laboratory for Atmospheric Science** NASA/Goddard Space




Flight Center, Greenbelt, MO. 20771.









Lacis, A. A., and J. E. Hansen, 1974: A parameterization for




the absorption of solar radiation in the earth's atmosphere,




J. Atmos. Sci . . 3J., 118-133.








Ponnamperuma, C.» 1981: The quickening of life, in Fire of




Life, Smithsonian Exposition Books, W. W. Norton and




Company, New  York, 118-125.









Stephens, G.  L.« 1978: Radiative properties of extended




water clouds: Part 11, J. Atmos. Sci.. 35,  2111-2132.








WHO/NASA,  1986: Atmospheric Ozone 1985, World Meteorological




Organization, Geneva, Global Ozone Research and Monitoring




Project, Report Number 16.

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                                                            15
                      List of Figure*




Figure 1.  Contours of total  column ozone (mi 11i-atmosphere-



centimeter*) •• a function of latitude and month  derived




from the SBUV instrument.








Figure 2.  The latitudinal and monthly distribution of UV-B



radiation at the ground computed for clear sky conditions




and a local time of 10:00 A.M.  Contour values*  in watts per



square meter* include all wavelengths between 290 and 320



nm.








Figure 3.  The ratio of solar energy flux in the UV-B from




Figure 2 to that in the UV-A  (320-400 nm) as a function of




month and latitude.  Values refer to radiation reaching the




ground for 10:00 A.M. local time and clear sky conditions.




Contours are in percent  (7.5 means that the UV-B energy flux




is 7.5V. of that in the UV-A).

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    N
     - COLUMN OZONE
   60
   20
LU
O
1   °
  -20
  -40
  -60
  -80
    S
       N
M    A   M   J    J
      MONTH
S    O
 Figure 1

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                                     .-2,
 N
CD
 85
 65
 45
 25
  5
 -5
-25
-45
-65
-85
    Total UV-B Flux  at Ground (W-M )
     N  0  J  F
                                     N
                                   0.4
                        I  i 	I  J   I x
               MAMJJASO
                  Month
                                     Figure 2

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       Ratio  UV-B  UV-A (Units: |Q  )
 N
a>
  -25-
  -45 ;c
  r-65
  -85
     N  0
JFMAMJJA
        Month
S  0
                                     Figure 3

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                  IMPORTANT NOTE TO READERS


     EPA hatt .submitted a draft document,  An Assessment of the
Risks'of Stehcospheric Modification,  to the Science Advisorv
Board today (October 23,198*), and also has released it for public
review and comment.  On November ?4 and 25 the Science Advisory
Board, chaired hv Dr. Margaret Kripke of The University of Texas
Departnent of Immunoloav, will meet to review the document.

     Until the SAR review is completed and the document revised,
the Assessment will not represent the official views of EPA.  The
estimates of risks in the document and the numbers contained in
it should be viewed as preliminary. and EPA requests that thev not
be cited or quoted.

     The document contains no recommendations for risk management
actions.  Rather, it is a compilation of scientific assessments of
risks. 'Vhen reviewed and revised it will serve as the basis for
EPA decisionmaking.  Thus the review that in now being initiated
is solely a scientific review.

     The Assessment builds on the atmospheric assessments conducted
bv the World Meteroloaical Organization, NASA, NOAA, CMA, and other
national and international scientific organizations. Much of
this previous work has already been peer reviewed.

     The Assessment covers and integrates information in a variety
of areas: industrial emissions of trace gases that can modify
t^e stratosphere; biogenic emissions of such gases; possible
changes in atmospheric concentrations which mav occur in response
to these atmospheres; the response of ozone in the stratosphere
to these changes; the response of the global climate system to
stratospheric modification and trace gas build up; basal and
squamous skin cancers; melanoma; immune suppression bv ultra-
violet radlation;crop and terrestial ecosvstem effects; aquatic
systems effects; the effects of UV-R on polvmers; the effects of
iTV-3 on trooospheric air quality; sea level rise; and the  effects
of climate chanee.

     In some cases qualitative assessments are made of these
impact areas; in other cases quantitative estimates are made.
In all cases, uncertainties are identified and their ramifications
examined. An effort  is nade to examine how these areas are
linked  together  so that  the risks can he examined over time.

     The general conclusion of the Assessment as  it now stands
is that a number of  health and welfare impacts are  likelv  if emis-
sions of chlorofluorocarbons grow.  A variety of uncertain factors are
found to be important in determining  the magnitude  of  likelv
effects, including:  the  future growth of greenhouse gases  that
could warm the earth which would counter ozone depletion;  the
exact dose-response  relationships  for health effects;  the  rate
of chlorofluorocarbons and halon growth; and  the  actual  response

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of che acraoaphere to changes in crace eases.  As it now stands che
Assessment uaes conventional atmospheric chemistry in assessing
risks, arguing chac coo Liccle is underscood ahouc che Ancarccic
ozone hole co use ic co re-evaluate currenc models of che resc
of che world.

     The reviewed and revised Assessment will serve as a basis
for decisionmaking in FPA'S regulatory program.   F.PA is scheduled
co make a proposal which suggescs regulations or states there
is no need for regulation on Mav 1,1987 and to make a final
regulatorv decision November 1 , 1^87.  In addition, internacional
negociacions are underway under che Uniced Nacions Environmental
Programme Co develop a prococol Co limic chlorofluorocarbons
globally.

     For addicional informacion call:

             John S. "offman
             Chairman,Scracospheric Proceccion Task Force
             EPA.PM-221
             401 M Street, SW
             Washington, DC 20460
             (202) 3*2-4036

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