United States
Environmental Protection
Agency
r Office of Policy
 & Resource Management
 Washington, DC 20460
 JtiJ JT//V. ,
October 1983
EPA 230-09-007
Revised
ENVIRONMENT,
 PROTECTION
Projecting
Future Sea Level Rise

Methodology,
Estimates to the Year 2100,
& Research Needs
                     DALLAS, TBM<

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                                                           C_
    PROJECTING FUTURE SEA LEVEL RISE


Methodology, Estimates to the Year 2100,

           and Research Needs
                   By

          John S. Hoffman, EPA
         Dale Keyes, Consultant
          James G. Titus, EPA
              A Report of:

      The Strategic Studies Staff
       Office of Policy Analysis
Office of Policy and Resource Management
  U.S. Environmental Protection Agency
      401 M Street, S.to. (PM-221)
        Washington, D.C.  20460
             (202) 382-5484

          2nd Edition, Revised

            October 24, 1983

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                         TABLE OF CONTENTS

                                                             Page

PREFACE  	    iii

ACKNOWLEDGMENTS  	    v

REPORT SUMMARY AND  FINDINGS	    vi

CHAPTER  1
INTRODUCTION  	    1

CHAPTER  2
THE SCIENTIFIC BASIS  FOR PROJECTING SEA LEVEL RISE  	    4

CHAPTER  3
THE APPROACH, ASSUMPTIONS,  AND MODELS USED TO
ESTIMATE SEA  LEVEL  RISE  	    13

CHAPTER  4
SEA LEVEL SCENARIOS TO THE  YEAR 2100 	    38

CHAPTER  5
IMPACTS  OF SEA LEVEL  RISE 	    41

CHAPTER  6
RESEARCH NEEDED  TO  IMPROVE
ESTIMATES OF  SEA LEVEL RISE 	    51

APPENDIX A  SUMMARY OF SEA LEVEL RISE SCENARIOS,
              INCLUDING  SPECIAL CASES OF INCREASED
              VOLCANIC ACTVITY AND CHANGES IN
              SOLAR IRRADIATION 	    59

APPENDIX B  MODELS, ANALYTICAL METHODS, AND
              ASSUMPTIONS USED FOR ESTIMATING
              THE SCENARIOS OF SEA LEVEL RISE 	    63

APPENDIX C  METHODS OF ESTIMATING
              SNOW  AND ICE  CONTRIBUTION 	  101

BIBLIOGRAPHY  	   115

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                              - Ill -






                             PREFACE






     The primary objective of this report is to estimate the




range of future sea level rise.  This information should help




coastal engineers, planners, coastal zone managers, water supply




and quality planners, and site planners to make better decisions




in coastal areas.  Scientists and federal research policy makers




can use this report in choosing research to improve sea level




rise estimates.




     This report has undergone an extensive peer review to ensure




its accuracy and completeness.  Nevertheless better estimates




of sea level rise will be forthcoming as scientific knowledge




improves.




     No EPA policy is implied in this document.  Comments are



welcome and should be sent to John Hoffman, PM-221, Strategic




Studies Staff, EPA, Washington, D.C.  20460.

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                             - V -






                         ACKNOWLEDGMENTS






     Several people made valuable contributions to this study.



Dr. Alan Truelove of Pechan and Associates did much of the early




computer programming.  Dr. Sergej Lebedeff, Dr. Gary Russell,




Dr. Andrew Lacis, and Dr. James Hansen of the Goddard Institute




for Space Studies (GISS) provided computer programs and technical




advice on the temperature-flux equations, thermal-expansion




model, and ice-sheet melting.  Dr. Robert Thomas and Dr. David




Thompson of the Jet Propulsion Laboratory provided information




on glacial processes.  Dr. William Emanuel of Oak Ridge National




Laboratories provided the computer program and technical advice




on the carbon-cycle model.  C02 projections were derived from




runs of a modified version of the World Energy Model provided by




the Institute of Energy Analysis, Oak Ridge Associated Universities,




Loren Dunn of EPA made valuable contributions to earlier versions




of this effort.   Wynne Cougill and Steven Seidel made editorial




suggestions.  Tom Glover provided graphics and Carolyn Acklin typed




numerous drafts.




     We would like to thank more than one hundred peer reviewers,




too numerous to name, who took time to comment on this report.




All errors, omissions and inaccuracies, however, are the




responsibilities of  the authors.

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                              - VI -
                   REPORT SUMMARY AND FINDINGS
     Concentrations of atmospheric CC>2 and other greenhouse gases
will continue to increase in coming decades.   Two National Academy
of Sciences panels have concluded that higher levels of these
gases will almost certainly produce a large global warming.
That warming, by thermally expanding the oceans and by causing
the transfer of ice and snow resting on land to the oceans,
should raise sea level substantially faster than the rise that
has taken place during the past century.

     Although current knowledge is inadequate to make a precise
prediction of future sea level rise, it is sufficient to predict
the likely range.  Many factors were considered in generating
the estimates of sea level rise contained in this report:
population and productivity growth, atmospheric and climatic
change, and oceanic and glacial response.  High and low assump-
tions for these principal determinants of sea level rise were
derived from the literature.  When linked together the various
assumptions allowed the estimation of high and low paths of future
sea level rise.  Based on this work, the following findings can
be stated:

(1)  GLOBAL SEA LEVEL WILL ALMOST CERTAINLY RISE IN COMING DECADES.

        A global rise of between 144 cm (4.8 feet) and 217 cm
        (7 feet) by 2100 is most likely.

        A global rise as low as 56 cm (1.9 feet) or as high as
        345 cm (11 feet) by 2100 cannot be ruled out.

        Along most of the Atlantic and Gulf Coasts of the United
        States, the rise will be 18 to 24 cm (0.6 to 0.8 feet)
        more than the global average.

(2)  ESTIMATES OF FUTURE SEA LEVEL RISE CAN BE USED TO REDUCE
     ITS ADVERSE IMPACTS.

        Sea level rise will increase shoreline retreat, erosion,
        flooding, and saltwater intrusion in coastal areas.
        Important economic impacts could result.

        Many, if not most of the adverse economic impacts of sea
        level rise can be avoided if timely actions are taken in
        anticipation of these effects.

        Professionals and policymakers need to assess the
        vulnerability of forthcoming decisions and the existing
        infrastructure to sea level rise.

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                            - VI 1 -
3)   THE RANGE OF FUTURE SEA LEVEL RISE ESTIMATES COULD BE NARROWED
    BY ACCELERATING RESEARCH.

    -  Differences in estimates of sea level rise are due to
       deficiencies in scientific knowledge and in the methods
       used for constructing estimates.  These deficiencies
       can be corrected.

       The most important research opportunities for improving
       sea level rise estimates are in estimating the transfer
       of ice and snow from land to sea, understanding the
       growth of the minor trace gases, and narrowing estimates
       of the sensitivity of the climate system to increased
       greenhouse gases.  Many opportunities exist for improving
       knowledge in these areas.

       Under current funding,  estimates of sea level rise will
       improve very slowly.

    -  Greater and more secure funding of interdisciplinary
       teams could produce a more rapid improvement in
       estimates.

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                           CHAPTER 1




                          INTRODUCTION






     Sea level can be expected to rise substantially throughout




the coming decades as a result of a global warming caused by




rising concentrations of atmospheric carbon dioxide,/ methane,



nitrous oxide, and chlorofluorocarbons.  The anticipated sea




level rise would increase coastal erosion and flooding;




groundwater tables would rise; and saltwater would intrude




into rivers, bays, and aquifers.^/




     Most coastal planners and decision makers are not considering




the effects of sea level rise.  Consequently, facilities are




being located without adequate consideration of the costs of




protecting them from erosion, flooding, or storm waves; important




environmental protection decisions are being based on inadequate




assessments of their future effectiveness; and entire communities




are being planned without adequate consideration of the




coastal works that will be necessary to protect their physical




infrastructures and capital investments.^/  Decision makers




and technical personnel need estimates of sea level rise to




evaluate the vulnerability of their decisions to changing risks.



     A tremendous reserve of knowledge has been accumulated by




natural and social scientists about the factors that will




determine sea level rise - population growth, climatic change,




oceanic heat absorption, glacial discharge, and atmospheric




composition.  This study uses that knowledge to project low and

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                              - 2 -


high ranges for future sea level rise.   Because the range of

assumptions used to project sea level rise varied from the very

conservative to the less restrictive, the estimates produced

here are likely to encompass the true rate of future sea level

rise.

     This report is organized as follows:

     o  Chapter 2 reviews the scientific basis for the
        belief that global warming will occur and cause sea
        level to rise.

     o  Chapter 3 presents the approach, the assumptions, and
        the models used to estimate sea level rise.

     o  Chapter 4 presents the results of our analysis: the
        low, high, and mid-range sea level rise scenarios.

     o  Chapter 5 reviews the research conducted on the impacts
        of sea level rise and discusses the need for further
        research on this subject.

     o  Chapter 6 presents a review of the research under way
        to improve estimates of sea level rise, along with
        options for accelerating the efforts to improve these
        estimates.

     o  Appendix A provides a summary of a larger set of sea level
        rise scenarios, including "special case" scenarios.

     o  Appendix 8 provides technical details of the models and
        assumptions used to generate the scenarios on thermal
        expansion.

     o  Appendix C provides details on the methods used for
        estimating snow and ice contributions, including a
        detailed analysis of the melting estimated under doubled
        CC>2 in a three-dimensional global climate model.

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                             - 3 -


Each chapter is followed by end notes that provide references

and explanations of the text.  It should be noted that the

estimates of sea level rise presented in this report differ

from those of the peer review and first edition (July, 1983)

because of improvements made in the treatment of trace gases.


                     END NOTES TO CHAPTER 1

1.   Charney, Jules, et al., 1979.  Carbon Dioxide and Climate:
    A Scientific Assessment.  Washington, D.C.:  National
    Academy of Sciences Press.  The warming predicted
    in this report is 1.5C to 4.5C for a doubling of
    C02.

2.   For an overview of the impacts of sea level rise and
    decisions that may be influenced, see:
    Titus, James G.,  et al., 1983.  Sea Level Rise Conference
    Document (draft).  Washington, D.C.: EPA., or
    Earth,  Michael C.  and James G. Titus,  (eds).  Sea Level
    Rise to the Year 2100.  Stroudsburg, PA: Hutchinson Ross
    (in press).

    For example, the 100-year floodplain defined in Federal
    Emergency Management Agency (FEMA)  maps is being used at
    EPA in making many decisions for coastal areas.  The maps
    have not, however, included any sea level rise in setting
    the flood boundaries.  Consequently, facilities may face
    greater hazards or have shorter useful lives than planned
    for.

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                             - 4 -






                           CHAPTER 2




       THE SCIENTIFIC BASIS FOR PROJECTING SEA LEVEL RISE






     Global sea level depends primarily on three factors:




(1) the total amount of water that rests in ocean basins rather




than on land; (2) ocean temperatures at various depths, which




determine ocean density and volume; and (3) the shape (bathymetry)




of the ocean floors.^/  Global warming could increase the




water resting in the oceans and the volume of that water, and




thereby raise sea level.  Because changes in bathymetry are




slow and unlikely to accelerate, this report considers only




the first two factors.




     This chapter discusses the scientific basis for expecting




a global warming to occur, and the linkages between that warming




and sea level.






GREENHOUSE GASES HELP DETERMINE THE PLANET'S TEMPERATURE




     The earth's temperature is determined by three factors:




the sunlight it receives, the sunlight it reflects, and the



infrared radiation absorbed by the atmosphere ._2/  Without the




influence of the atmosphere, incoming visible radiation (in




the form of sunlight) and outgoing radiation (in the form of




invisible infrared radiation) would balance to yield a certain




surface temperature.  However, the atmosphere contains gases




such as CO2 and water vapor that absorb some of the infrared




radiation.  These gases are warmed by the radiation and radiate




energy back to the earth's surface, raising its temperature.

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                                - 5 -


The  larger the percentage of  infrared radiation blocked by

the  atmosphere,  the warmer  the earth's surface temperature.

This  feature of  CC>2 and certain other gases is known  as the

"greenhouse effect."

      The greenhouse effect  is an important  factor determining

a planet's temperature, as  observations of  the temperatures of

other planets confirm (see  Table 2-1)./


                              TABLE 2 - 1

     THE GREENHOUSE EFFECT ON THE  INNER PLANETS: PREDICTION AND OBSERVATIONS

VENUS
EARTH
MARS
Sunlight
Received
(watts per
square meter)
2613
1367
589
Sunlight
Reflected
(percentage)
75
30
15
Temperature
Without An
Atmosphere
-40C
-18C
-56C
"Opacity"
Of Atmosphere
To Infrared*
~ 100
~ .1
Predicted
Temperature
With Simple
Models**
429C
17C
-52C
Actual
Temperature
427C
15C
-53C
                 Higher number indicates greater ability to trap infrared radiation.
                 *Average of two simple models: radiative equilibrium and corrective
                 equilibrium.
             Source: Modified from Hansen, J. Lacis, A. and Rind, D., "Climate Trends Due to
                 Increasing Greenhouse Gases", Coastal Zone 83. New York: ASCE, 1983.
Contrary to popular  belief, Venus is not hotter than Earth

because  it is nearer to the sun,  but because its atmosphere is

97 percent CC>2.  Although Venus  receives more sunlight

(2613  watts per square meter)  than Earth (1367 watts per  square

meter),  it reflects  75 percent of this radiation (which explains

its brightness), compared with 30 percent  for Earth.   If  the

atmospheres of the planets did not differ  in their ability to

absorb infrared, Earth, with  its  lower reflectivity, would be

23C degrees warmer  than Venus.   Similarly,  with its very low

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                             - 6 -






reflectivity, Mars would be only 15C cooler than Earth.




     However, these planets have atmospheres with very different




capabilites of absorbing infrared.  The atmosphere of Mars has




almost no water vapor and a low level of CO2.  According to




simple models of the greenhouse effect, its temperature should




rise only slightly.  In contrast, according to the same models,




Venus's atmosphere of 97 percent CC>2 should raise its temperature




to a scorching 432C (775F), and Earth's atmosphere of 0.03




percent CC>2 and considerable water vapor should warm it by




30C to an average of 17C (63F).  Space probes to Mars and




Venus and measurements on Earth confirm that their actual




temperatures rise as predicted.




     This and other evidence has led scientists to believe




that as atmospheric levels of CC>2 and other greenhouse gases




increase, Earth's temperature will rise.  Using more comprehensive




models of the greenhouse effect, it has been relatively simple




to estimate that if no other changes take place in atmospheric




composition (i.e., concentration of other greenhouse gases) or




the albedo (reflectivity) of the planet, a doubling of atmospheric




CC>2 concentrations will warm the earth's surface temperature




1.2C.f/




     Projecting the extent of the future warming is complicated




by the fact that the initial warming will change reflectivity




and atmospheric composition in a way that will almost certainly




amplify the direct warming.  For example, the 1.2C temperature

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                             - 7 -






rise will increase water vapor levels in the atmosphere,




trapping more infrared radiation, and will also melt snow and




ice, decreasing the reflectivity of the earth.  Other climatic




effects, such as changes in cloud cover and cloud heights,




could increase or diminish these amplifications by amounts




that cannot be predicted accurately.



     The 1979 report of the National Academy of Sciences (NAS),




prepared by a review panel of leading climatologists, reflected




the agreement of the scientific community on the effects of




these feedbacks.  The panel members summarized their view by




stating:  "We have tried but have been unable to find any




overlooked physical effect that could reduce the currently




estimated global warming due to a doubling of C02 to negligible




proportions. . . . "jV  Unfortunately, the panel's agreement




that a large warming will occur did not permit it to develop




a narrow range for the estimated global temperature increase.




However, it was able to conclude that the earth's equilibrium




temperature increase for doubled CC>2 would be at least 1.5C




(2.7F)  and not more than of 4.5 (8.1F).




      Since 1979, scientific consensus has continued to grow




that the warming will be significant.  In 1982, a second NAS




panel reviewed new evidence and confirmed the conclusions of




the first panel._/  More recently, the World Meteorological




Organization and other researchers have concluded that other



gases whose atmospheric concentrations are increasing could




double the warming from CO9 alone. /  Thus, by the time CO.-,
                          ^                              ^

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doubles, the earth's total equilibrium temperature increase




is likely to be between 3C to 9C (5.4F to 16.2F).






CONCENTRATIONS OF GREENHOUSE GASES WILL ALMOST CERTAINLY DOUBLE




IN THE NEXT CENTURY



     In the past 180 years, atmospheric CO2 appears to have




risen approximately 20 percent, from between 260 and 290 ppm




to 340 ppm.  Very accurate monitoring began in 1958; since then,




atmospheric C02 has increased 8 percent, from 315 ppm to




340 ppm._^/




     Atmospheric levels of other gases have also risen.  Methane




increased annually by about 1 to 2 percent from 1970 to 1980,




chlorofluorocarbons by about 6 percent over the same period.




and nitrous oxide by about 0.2 percent per year from 1975




to 1980.V



     Economic activities have caused most of these increases.




For CO2, the most important cause of emissions has been the



combustion of oil, gas, and coal, with deforestation probably




contributing a small percentage.  Burning fossil fuels (hydro-




carbons) oxidizes carbon (C   + 2O   -> CO2), inevitably



releasing CO2-




     Future energy use and fuel selection will thus be the




primary determinants of the rate of C02 emissions.  Because




fossil fuels have important competitive advantages and play a




critical role in existing energy systems, their use is expected




to grow even if radical policies are undertaken to curtail their




use.  For example, Seidel and Keyes found that even a 300 percent




worldwide tax on fossil fuel use would delay a 2C temperature

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                             - 9 -






rise only five years.10/



     Because only a fraction of the emissions will remain in the




atmosphere, concentrations of atmospheric CC>2 cannot be predicted




by emissions alone.  Nevertheless, although disagreement exists




about the exact fraction, an almost universal consensus exists




that it will be great enough to ensure that atmospheric CC>2




levels will at least double in the next century.H/




     The future rates of increase for the other greenhouse gases




are less certain.  Much less is known about the sources




of methane, nitrous oxide, and chlorofluorocarbonsj^/ than the




sources of CC>2.  Furthermore, scientific understanding about




the fate of these gases once they enter the atmosphere is also




insufficient.  Nevertheless, atmospheric concentrations of




these gases are likely to increase substantially, and in the




case of chlorofluorocarbons, probably at a rate faster than CC>2.






THE OCEANS WILL ALSO INFLUENCE THE RATE OF FUTURE WARMING




     The rate of future warming will depend on more than the




earth's equilibrium temperature sensitivity and the rate of



increase in atmospheric C02 and other greenhouse gases.  It




will also depend on the time it takes for the climatic system




to reach the equilibrium temperature.



     The most important factor delaying the warming will be




the oceans' capacity to absorb heat that would otherwise warm




the atmosphere.^/  As surface air temperatures increase, a




temperature difference will develop between the surfaces of




the atmosphere and the oceans, causing heat to be moved to

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                             - 10 -


the oceans.  This heat will slowly pass downward to the lower

and cooler layers.  In this way, the oceans will act as heat

"sinks", somewhat delaying the full atmospheric warming.


EXPECTED TEMPERATURE INCREASES WILL BE SIGNIFICANT

      The expected global warming will be large compared to

historical temperature changes, and even more significant

compared to historical rates of temperature change.  In the last

two million years, the earth nas never been more than 2 to 3C

warmer than it is today.^/  In the last hundred thousand years,

it has been at most 1C warmer, and in the last thousand years,

at most 0.5C warmer.  Since the Wisconsin Ice Age (18,000 years

ago), the earth has warmed about 4C,/ and in the last century,

about 0.4C._J_^/  The projected warming for the next century would

be ten times as rapid as the Historical warming trend.

     The expected warming will also be large compared to geo-

graphical temperature differences.  A 3C warming would leave

San Francisco as warm as San Diego is today.  A 9C warming

would raise New York City's average temperature to the current

temperature of Daytona Beach, Florida.


THERMAL EXPANSION AND GLACIAL DISCHARGES COULD RAISE SEA LEVEL

     As global temperature rises, the sea level can be raised

in two ways:

     o  Thermal expansion

        Warming will decrease the density of ocean water, and
        thus increase its volume.  Because the same water will
        take up more space, the levels of the oceans will
        rise.  The rate of this rise directly depends on the
        amount of heat the oceans absorb.

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                             - 11 -
     o  Transfer of snow and ice from land to sea

        Warming can transfer snow and ice from land to sea by
        melting (if the meltwater runs off into the ocean) or
        deglaciation (glaciers breaking up or moving more
        rapidly into the ocean).  Sea level will rise as a result
        if these effects are not offset by the additional
        accumulation of snowfall on land.  Both of these effects
        are likely to occur with the warming predicted for the
        next century.  The rate at which they would occur,
        however, is less certain than that of thermal expansion
        and may not be proportional to the rate of warming.
        Deglaciation, in particular, may be a phenomenon in
        which a threshold exists.  Once this threshold is
        passed, the deglaciation may become a self-reinforcing
        process, whose timing depends on many things other
        than the magnitude of the warming.

     Geologic history indicates that these physical mechanisms

describe the behavior of the earth.  During warmer periods in

earth's history, sea level has been higher than in colder

periods, varying by over one hundred meters.

                     END NOTES TO CHAPTER 2

_!/   Winds, currents, and land subsidence and emergence may
     cause local sea level to change at rates different from
     global sea level.  For specific applications, the global
     estimates in this document should be adjusted by comparing
     historical local and global sea level trends.

_2/   Hansen, James E., A. Lacis, and D. Rind, 1983.  "Climatic
     trends due to increasing greenhouse gases," in Coastal
     Zone '83, Orville T. Magoon, ed.  New York: American
     Society of Civil Engineers. 3:2796-810.

V   Ibid.

V   Ibid.

_5/   Charney, Jules, et al., 1979.  Carbon Dioxide and Climate:
     A Scientific Assessment.  Washington, D.C.:  National
     Academy of Sciences Press.

6/   Smagorinsky, J. , 1982.  Carbon Dioxide and Climate;  A
     Second Assessment.  Washington, D.C.:  National Academy of
     Sciences Press.

7/   World Meteorological Organization, Sept. 1982.  WHO Global
     Ozone Research and Monitoring Project, Report No. 14 and
     Lacis, A., et al., 1982.  "Greenhouse effect of trace gases,
     1970-1980."  Geophysical Research Letters.  81:10:1035-8.

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                             - 12 -
Q_/   Keeling, C.D., et al., 1976. "Atmospheric carbon dioxide
     variations at Mauna Loa Observatory, Hawaii." Tellus,  28,
     and Rotty, Ralph, 1979. "Energy demand and global climate,"
     in Man's Impact on Climate, Wilfred Bach, et al., eds.  New
     York: Elsevier Scientific Publishing.

9_/   World Meteorological Organization, op. cit.

10/  Seidel, Stephen and Dale Keyes, 1983. Can We Delay A
     Greenhouse Warming? Washington, D.C:  U.S. Environmental
     Protection Agency.  These authors demonstrate that strong
     efforts to curtail fossil fuel growth, such as a tax that
     quadruples the costs of these fuels, will delay the increase
     in emission levels and temperature rise by only a few years.
     An unconventional counterview that argues that it is theo-
     retically possible to reverse the growth is provided in
     Lovins, A., et al., 1981.  Least Cost Energy.  Andover,
     Mass: Brick House Publishing Company.

ll/  Keeling, C.D., op. cit., and Rotty, R., op. cit.

12_/  Chlorofluorocarbons will have two effects on climate.
     Their radiative effect will be warming.  Although ozone
     absorbs infrared radiation, the depletion of ozone in the
     upper stratosphere by CFCs will have a slight warming
     effect; the increased incoming ultraviolet radiation will
     be greater than the increased outgoing infrared radiation.
     Other perturbants, such as nitrogen oxides from airplanes,
     may increase ozone in the lower stratosphere, which because
     of pressure broadening, would make ozone a better infrared
     obsorber, thus making increases at this lower altitude pro-
     duce a net warming.  Although the total temperature effect
     of the changes in stratospheric ozone are still uncertain,
     the warming contributed by this factor may be significant.
     See Wuebbles, D., 1983.  "Effect of coupled anthropogenic
     perturbations on stratospheric ozone," Journal of Geophysical
     Research.  88:C2:1444-1456.

13/  Charney, J., op. cit., and Smagornisky, J., op. cit.  It
     is estimated that the oceans take several decades to feel
     the full effect of atmospheric warming.  Thus, rnucn of
     the equilbirium warming from greenhouse gases added to
     the atmosphere in the 1970s has not yet occurred.

j.4/  Flohn, H., 1981.  Life on a Warmer Earth.  Laxenburg,
     Austria: International Institute for Applied Systems
     Analysis.

15/  Hansen, James E., A. Lacis, and D. Rind, 1983. op. cit.

16/  Hansen, James E., A. Lacis, and D. Rind, 1981.  "Climate
     impact of increasing atmospheric carbon dioxide," Science.
     213:4511:957-66.

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                             - 13 -
                           CHAPTER 3

             THE APPROACH, ASSUMPTIONS, AND MODELS
                USED TO ESTIMATE SEA LEVEL RISE
     Estimating global sea level rise requires considering all

of the possible changes in the social and natural systems that

could influence future climate and sea level./  Existing

scientific knowledge is inadequate to make a precise prediction

of the extent of these changes.  Consequently, we generated a

range of estimates, called scenarios.

     Each scenario used a different set of assumptions  (see

Figure 3-1).  For each factor that could affect sea level, a

range of assumptions was developed by consulting the literature

and the appropriate scientists.  Thus, the full set of

assumptions covered the likely ranges for each factor, although

not necessarily the most extreme possibilities.

     Models were selected that allowed various assumptions

to be combined to generate yearly estimates of sea level

rise.  The models were chosen for their ability to accomplish

this task in a reliable, flexible, and cost-effective manner.

     Many scenarios were generated, but four critical ones

were named.  The "low scenario" consists of the most conservative

assumptions for each factor, while the "high scenario" consists

of the least conservative.  Although the determinants of sea

level rise are not likely to be all at the high ends or low

ends of their ranges, these possibilities cannot be ruled out.

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                              - 14 -
                            FIGURE 3-1

               SUMMARY OF HIGH ALS1D LOW ASSUMPTIONS
                 USED TO ESTIMATE SEA LEVEL RISE
                                       Assumption
                               Low
High
Population Growth 	  All scenarios assumed the world
                            will reach zero population growth
                            by 2075

Productivity Growth	  2.2% per year;        3.5% per year;
                            decreases to          decreases to
                            1.7% by 2100          2.2 % by 2100

Energy Technologies	  Best estimate,        Best estimates
                            Nuclear costs halved
                            arbitrarily.

Unexpected Additions	  None                  None
To Fossil Fuel Base

Energy Conservation	  All Countries Move Toward High Efficiency
                            (60% improvement in energy efficiency)-

Fraction Airborne (CO2)   53%                   ORNL Model; 60%
                                                  increases to 80 %

Nitrous Oxide	  0.2% per year         0.7% per year
                            growth                growth

Chlorfluorocarbons	  Emissions increase    Emissions increase
                            0.7% of 1980 level    3.8% of 1980 level
                            per year              per year

                            60-year half-life for CFC13 and 120-year
                            half-life for CF2Cl2

Methane	  1% per year growth    2% per year growth

Temperature Sensitivity	  1.5C for CO2         4.5C for CO2
                            doubling              doubling

Heat Diffusion of Ocean	  1.18 cm2/sec          1.9cm2/sec

Glacial Discharge	  Equal to Thermal      Twice Thermal
                            Expansion             Expansion

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                             - 15 -






     Two mid-range scenarios were developed.  They differ only




in their estimates of snow and ice contributions to sea level




rise; the estimates of the mass transfer of ice and snow from



land to sea are much less reliable than estimates of thermal




expansion.  The mid-range scenarios used assumptions that fell




between those used in the low and high scenarios (except in




the case of fraction airborne, where we used the ORNL model).




Although it is currently impossible to estimate probabilities,




we believe that the actual sea level rise will probably fall




between the two mid-range scenarios.




     The remainder of this chapter presents the assumptions




and models used to develop the scenarios.  Technical details




about the assumptions and models are provided in Appendix B.






YEARLY RISES IN SEA LEVEL WERE SIMULATED




     The yearly rise in sea level can be estimated by project-




ing yearly changes in the natural systems that determine it.




Four systems must be considered: atmospheric composition,




the climate, the oceans, and the cryosphere (the part of the




world that is ice or snow).  Changes in the atmosphere will




produce changes in temperature, which in turn produce thermal




expansion and the transfer of snow and ice from land to sea




(Figure 3-2).  Below, we also discuss possible changes in




other factors that determine global temperature, such as changes




in solar irradiation or volcanic aerosols.  (A permament




increase in the average level of aerosols would block sunlight




and cool the earth.)

-------
                                - 16 -
Atmospheric
Composition
 Other
 Climate
 Forcings
                              Figure 3-2
                       Yearly Modeling Sequence
                     Temperature
                      Change
Thermal
Expansion
Snow/Ice
Transfer
To Sea
                   Global Sea
                   Level Rise
    Atmospheric Composition

         Projecting changes in the atmospheric concentrations of

    CC>2 and other greenhouse gases required projecting emissions of

    these gases and their fate as a result of atmospheric chemistry

    and other biogeochemical cycles that can create and destroy

    them or remove them from the air.  In general, only a percentage

    of the emissions of each gas is retained in the atmosphere in

    a chemical form that absorbs infrared radiation.

         Estimating future C02 emissions required estimating future

    economic growth and fuel use.  Because economic growth is

    determined by the rate of population increase, productivity

    growth, and technological change, it was necessary to make

    assumptions about each of these factors and to integrate them

    in a consistent manner.

-------
                             - 17 -


     The following assumptions were used:

       0  Worldwide Population Growth was assumed to level
          off by 2075 for all scenarios, based on the work
          of Keyfitz et al ./

       0  Productivity Growth for labor was assumed to decline
          for both the high and low scenarios.

             -  In the high scenario, the growth rate
                began at 3.5 percent (per year) in 1980
                and linearly decreased to 2.2 percent by 2100.

                In the low scenario it linearly declined from
                2.2 percent in 1980 to 1.7 percent by 2100.

          The past 30 years have experienced a higher rate of
          productivity growth than either of these assumptions.

       0  Energy Production Technologies for various
          fuels were assumed to improve:

                for the low scenario, a best guess of future
                technologies and costs was used.

                for the high scenario the same estimates
                were used except the cost of nuclear
                energy was assumed to be cut in half in 1983.

       0  Fossil Energy Resources were assumed to stay at
          current levels with no new major discoveries.

         Energy Use per unit of output (measured in GNP)
          was assumed to decline by over 60 percent between
          1975 and 2100, reflecting two assumptions:
          (1) as economies develop, they will become more
          service oriented, and (2) energy technologies
          will become more efficient, partly in response to
          higher prices.

     A world energy model developed by the Institute for Energy

Analysis at Oak Ridge Associated Universities was used to inte-

grate the assumptions.^/  The model divides the world into nine

regional sectors.   Market mechanisms are used to select energy

sources and trade supplies in and between each region.  C02

emissions are generated by using well-established coefficients

for each fuel.

-------
     As mentioned, not all the CC>2 emissions remain in the

atmosphere.  Some are removed by green plants, and some are

absorbed by the oceans.  Unfortunately, knowledge of these

percentages is uncertain because the movement of carbon between

various "storage compartments" in the earth (the oceans,

biosphere, and the atmosphere) is only partially understood.

Two assumptions were made for predicting the fraction airborne:

     o  For the high scenario, a model of the carbon cycle
        developed at Oak Ridge National Laboratories (ORNL)
        was used ,_4/  The model represents, at a very high
        level of aggregation, many of the physical and
        chemical mechanisms that regulate the exchanges of
        carbon between the various natural compartments that
        absorb and release it.  The fraction airborne increased
        over time from 60 to 80 percent.

     o  For the low scenario, the percentage of carbon dioxide
        remaining in the atmosphere was assumed to be equal to
        its historical average of 53 percent.^/  This assump-
        tion is conservative for several reasons.  Like a
        sponge, the upper layers of the oceans have a limited
        absorption capacity.^/  Thus, as the emissions of
        CO2 increase, the percentage taken up by the oceans
        should decrease.  Also, warming of the oceans and the
        resulting changes in circulation could lower the capacity
        of the oceans to absorb C02._

     o  For the mid-range scenario, the ORNL model was used.

     High and low assumptions about CO2 emissions and the

fraction airborne were used to generate high and low estimates

of the yearly increase in atmospheric CO2  Under the low scen-

ario, atmospheric concentrations of CO2 will double by 2085,

for the high scenario, by 2055.

-------
                             - 19 -


     Projections of the concentrations of chlorofluorocarbons

and other trace gases involved much less sophistication than

our projections of CO2 concentrations.^'

     o  The low scenario assumed that emissions of chloro-
        fluorocarbons grew at 0.7 percent of the 1980 level
        (1.8 million kg) annually until being capped in 2020
        and that CFC13 (CFC-11) and CF2C12 (CFC-12) have
        half-lives of 60 and 120 years, respectively.

     o  The mid-range scenario assumed that emmissions of
        CFC13 and CF2C12 grew at 2.5 percent of the 1980 level
        (6.4 million kg) per year until 2020 and then are
        capped.

     o  The high scenario assumed that emissions of CFC13
        and CF2C12 grew at 3.8 percent of the 1980 level
        (9.8 million kg) per year until being capped in 2020.

The low assumption implies that atmospheric concentrations

will gradually approach an equilibrium concentration by 2100.

Although the high assumption implies that concentrations will

grow faster, it is not really an upper bound for likely future

concentrations.  It is possible that chlorofluorocarbon

emissions will never be capped, or that their use in developing

countries will parallel that of the developed countries

(a growth not anticipated in the high scenario).

     Nitrous oxide concentrations are also assumed to increase:^/

     o  The low scenario assumed 0.2 percent per year growth.

     o  The mid-range scenario assumed 0.45 percent per year
        growth.

     o  The high scenario assumed 0.7 percent per year growth.

-------
                             - 20 -


     Finally, methane is also assumed to grow:10/

     o  The low scenario assumed 1.0 percent growth per year.

     o  The mid-range scenario assumed 1.5 percent growth per
        year.

     o  The high scenario assumed 2.0 percent growth per year.

     Our analysis did not consider changes in ozone concentra-

tions at different altitudes, which may prove to be important.

Ozone depletion in the upper stratosphere caused by chlorofluro-

carbon emissions will tend to have a warming effect because

the loss of ozones'  infrared absorbing capibility at this

altitude will be more than offset by the additional U-V energy

allowed to penetrate to the earth's surface.  Higher ozone

levels in the lower stratosphere and upper troposphere, caused

by NOX emissions from airplanes, will cause additional warming

because at those altitudes the additional infrared that is

absorbed outweighs the reduction in ultraviolet that penetrates

to the surface._/ other minor greenhouse gases, such as CCl/,

CF4, NH3, and C2C13F3 (CFC-113) could also contribute to the

warming, but were not considered in this analysis.


Climatic Responses

     As the atmospheric abundance of gases that absorb infrared

radiation increases, the earth's temperature will rise.  The

extent of the ultimate warming will depend on how much the

initial warming alters the levels of other infrared-absorbing

gases such as water vapor, or its reflectivity, by changing

ice and cloud cover.l^/  These "feedbacks" may amplify the

-------
                             - 21 -


initial warming considerably.  Because the magnitudes of these

factors are not precisely known, a large range of temperature

changes was used to represent all of these uncertainties:

     o  The high scenario used the National Academy of Sciences'
        (NAS) estimate of a 4.5C rise for a CC>2 doubling.

     o  The mid-range scenario used the NAS middle estimate
        of 3.0C.

     o  The low scenario used the NAS low estimate of 1.5C.

     To integrate these assumptions about thermal sensitivity

and the changes in atmospheric concentrations, we used an equa-

tion obtained from the Goddard Institute for Space Studies

based on a one-dimensional radiative convective model.  (See

Appendix B).   Coupled with a box-diffusion model that

calculates the heat absorbed by oceans, the equation allowed a

consistent integration of changes in greenhouse gases, thermal

sensitivity,  and the oceans' absorption of heat.13/


Thermal Expansion of Ocean Waters

     Because  ocean waters circulate slowly, the deeper layers

of the ocean  will warm very slowly, and for our purposes, can

be ignored.  As the top layers warm, however, the ocean's

volume will expand.  Although the percentage expansion is

small, the resulting sea level rise could be significant from

the human perspective.

-------
                             - 22 -


     As discussed, the downward movement of heat was projected

with a simple box diffusion model.  While this model does not

represent the ocean circulation processes that actually

transport heat, it is probably a good surrogate for the likely

effects of such processes for the time span of 100 years.

Nevertheless, to ensure the validity of. the sea level rise

estimates, we used different assumptions:

     o  For the high assumption, a rate of heat diffusion
        compatible with higher estimates of observed movement of
        chemical and radioactive tracers was used (1.9 cm^/sec).

     o  E'or the low assumption, a rate of 1.18 cm^/sec was used,
        which is compatible with a more conservative
        interpretation of tracer studies.14/

     o  For the mid-range assumption, the average of the high
        and low assumptions (1.54 cm^/sec) was used.

     The expansion of the seas was then computed using known

coefficients of expansion for the temperature, salinity, and

pressure of each ocean layer.  We did not disaggregate thermal

expansion to reflect the geographical variation of ocean

temperatures.  Because water expands by different amounts at

different temperatures, disaggregation would improve sea level

rise estimates.  However, the one-dimensional description of

temperature and salinity provides a good first approximation.


The Cryosphere

     Most discussions concerning sea level rise have focused

solely on the possible contributions of ice and snow resting

below sea level in West Antarctica moving into the sea,

-------
                             - 23 -


while only a few articles have discussed thermal expansion.

Yet no glaciologist has estimated the potential contributions of

ice and snow to sea level in the next century.  In this section,

we discuss the several methods developed to perform this task.

Because the contributions of ice and snow to sea level rise could

be more important than thermal expansion, these methods should

be improved as soon as possible.


     Size and Potential Source of the Land-Based Contributions

     The amount of water contained in the ice and snow of

Antarctica, Greenland, Northern Europe, Asia, and North America

or in alpine glaciers is equivalent to about 70 meters of sea

level rise  (see Table 3-1).  The Arctic Ocean consists of sea

ice; therefore, its melting or breakup would not directly

raise sea level.

     Global warming can influence the percentage of the earth's

water resting on land by several means:

     o   It can melt ice and snow.  Melt water that runs off
         into the sea will raise sea level.

     o   It can increase the rate of flow of land-based ice
         sheets toward the sea.  This deglaciation would add
         ice to the oceans, thereby raising sea level.

     o   It can cause the atmosphere to carry more moisture to
         cold areas in the form of snow, thereby increasing
         snowfall accumulation and decreasing sea level.

Estimates of ice and snow contributions to sea level rise

can be made for each of these sources separately, or through

an aggregate estimating method.  Both approaches are used

here.

-------
                                   - 24 -


                                 TABLE 3-1

                        DISTRIBUTION OF ICE AND SNOW
                                         Area
                                 Volume
               Sea-Level
               Equivalent
Snow and Ice on Land
  Antarctica 1,2
  Greenland
  Small Ice Caps and Mountain Glaciers

Ground Ice (Excluding Antarctica)
  Continuous
  Discontinuous
Sea Ice

  Arctic:

  Antarctic:
Max.
Min.
Max.
Min.
                                         106km2
                          13.9
                           1.8
                           0.5
                           7.6
                          17.3
15.5
 8.4
20.0
 2.5
                                 106km3
                                 water
         28.0
          2.7
          0.24
5.0x104
2.0x104
3.0x104
5.0x103
Total Land Ice, Sea Ice and Snow
                                                             m
            70
             7
             0.3
                      1.0
Jan.

July:

Global Mean
N.
S.
N.
S.
Annual
Hemisphere
Hemisphere
Hemisphere
Hemisphere

58
18
14
25
59
1  Excludes peripheral, floating ice shelves (which do not affect
   sea level).

2  Roughly 10  percent of the Antarctic ice is in West Antarctica,
   and 90 percent is in East Antarctica.

Source:  N. Untersteiner,  "Sea ice and ice sheets role in climatic
         variations, Appendix 7," of GARP Pub. series 16: Physical
         Basis of Climate  and Climate Modeling.  World Meteorological
         Council of Scientific Unions, 206-24.  April 1975.

-------
                             - 25 -






     Predicting Snow and Ice Contribution Using Climate Models




     The most comprehensive tool for understanding climatic




change is the three-dimensional general circulation model




(GCM).  By solving a series of equations that represent the




fundamental laws of atmospheric structure and motion, such




models simulate the earth's weather on an hour-by-hour basis,




moving moisture and heat upwards and downwards, north and south,




east and west.  Although the models represent the actual atmos-




phere, solar irradiation, and the reflectivity of the earth with




a fair degree of accuracy, the topography used is coarse;




variations in large geographic regions are averaged together,




and each grid is treated as a plateau.




     By accumulating hourly and then daily weather statistics,




these models can generate years of data that represent the




climate of different regions.  Since the models do not yet




represent all of the processes that determine climate, one




finds some discrepencies.  Nevertheless, in most aspects, a




GCM simulates weather fronts realistically: rain, snow, heat




and cold are generated by the same mechanisms active in the




actual climate system.  By comparing projections of these



models (assuming today's CC>2 levels) against observed weather




and climate, GCMs ahve been shown to accurately reproduce




the world's weather patterns.

-------
                             - 26 -






     Several research groups have developed GCMs to explore




the effects of changes in the atmosphere's composition:




NOAA Geophysical Fluid Dynamics Laboratory (GFDL), the National




Center for Atmospheric Research (NCAR), and the Goddard Insti-




tute for Space Studies (GISS) have undertaken three well-known




efforts in the United States.^/  Each group has run its GCM




assuming the current atmosphere and doubled CC>2 concentrations.




While some of the model predictions differ about climatic




change, they are qualitatively similar.



     The GISS group has used its model to estimate the size




and geographical distribution of snow and ice in a warmer




world.  In fact, the group has done two doubled CC>2 experiments,



which differed only in their techniques for computing sea ice,




a key factor in determining the effects of atmospheric change




on Antarctica.  One model run started with somewhat more sea




ice, and one with somewhat less sea ice than currently exists in




Antarctica.  This provided a method to check the sensitivity



of the models to this initial condition.




     Both doubled C0'2 runs showed a substantial net melting




of land-based snow and ice.  Both "control" runs (i.e., using




current atmosphere and climate) showed nearly stable amounts




of snow and ice.  Thus, the results of the four runs increase




our confidence that global warming will significantly decrease




snow and ice resting on land.  The run deemed most accurate




showed a melting equivalent to a sea level rise of about one

-------
                             - 27 -






centimeter per year.^2/  (See Appendix C for details and



possible sources of error.)  Snowfall accumulation increased




in the run, but was overwhelmed by additional melting.  This




contrasted sharply with the results of the model runs using




today's temperature and CC>2, which showed almost stable




levels of ice and snow on land.




     These results need to be analyzed in greater depth than




was possible for this study, and model experiments should be




made with a more realistic treatment of ice sheet decay.




Studies should also be made using other GCMs, and collateral




evidence should be reviewed and integrated into the analysis.




Nevertheless, these two GCM experiments provide evidence that




a global warming would decrease the mass of the ice sheets




by the melting and ensuing runoff.




     One aspect of the GISS results that particularly needs




more analysis is the runoff of meltwater, not all of which




will escape to the sea.  In many fringe areas of the ice sheets,




where much of the melting will take place, most of the water




probably will run off into the ocean; however, the percentage of



runoff will be low in the antarctic interior.  Water that does




not run off will percolate into the ice and refreeze, which may




cause ice softening and crevasing.




     Glaciologists should use GCM outputs and information about




glaciers and the topography of the land underlying ice to




estimate the percentage of meltwater that will run off.  They




should also consider the degree to which changes in the physical

-------
                             - 28 -


characteristics of the ice sheet induced by refreezing will

lead to faster deglaciation. (A brief discussion appears in

the next section and in Appendix C.)

     Another important feature of the GISS modeling is that the

estimated melting of one centimeter per year was computed on

the basis of a world whose atmospheric levels of C02 have

already doubled.  Thus, the GCM results do not directly provide

a realistic time trend of sea level rise as CC>2 and other

greenhouse gases approach and then exceed this level of warming.

Computation of a time trend would have required estimating

(1) the percentage of the meltwater that runs off into the

oceans; (2) the degree to which the meltwater that does not

run off accelerates glacial movement; and (3) the scale of

melting that occurs as the earth warms.  These steps could not

be undertaken in this study.  Thus, instead of directly using

the one centimeter per year of melting as a scenario, the GISS

output was taken as a qualitative confirmation that ice and

snow can be expected to contribute significantly to sea level

rise.

     Deglaciation as a Source of Land-to-Sea Transfer of
     Snow and Ice

     The possibility of a major deglaciation (the removal of

ice by a process other than melting in place) cannot be ignored.

Geological evidence suggests that changes in global temperatures

can cause the large ice sheets that rest on Antarctica to break

up and "fall" into the oceans.  For example, during the last

-------
                             - 29 -






interglacial (120,000 years ago), which was about 1C warmer




than today, the West Antarctic ice sheet may have completely




disappeared.^/




     Several ice sheets that contain significant quantities of




water are thought to be vulnerable to warming.  Thousands of




feet thick and resting mainly on land, these sheets are held




in place and prevented from entering the ocean by floating




"ice shelves" and pinnings below sea level.  As global warming




occurs, the waters around these shelves and pinnings may become




warmer and melt them, allowing the ice sheets to begin to slide




into the oceans.  Furthermore, meltwater that does not run off,




but percolates into the sheets and then refreezes, will tend to




soften the ice, making rapid movement of ice more likely.




Polar warming, which may be several times the magnitude of the




average global increase, thus makes it possible for "the bottle




to be uncorked."




     Because it is marine-based (resting on the ocean floor),



the ice sheet most vulnerable to such a deglaciation is the




West Antarctic ice sheet.  If all of that ice enters the ocean,




sea level will rise five to six meters.  Bentley has estimated




500 years, and Hughes 200 years, as the earliest time this




could possibly happen.^/  Although both estimates were




made in the absence of detailed information about melting




rates, sea ice retreat, and ocean and air temperatures, the




possibility of a complete disintegration in 200 to 500 years




cannot be ruled out.

-------
                             - 30 -


     Accurate estimation of the partial deglaciation of the

West Antarctic, East Antarctic, and Greenland ice sheets for

the next 120 years will require detailed studies of the specific

ice sheets.  Such studies should consider such factors as the

predicted temperature of the upper surface of the ice, surface

precipitation rates, ocean water temperatures, melting of ice

shelves from the bottom, speeds of ocean currents and their

ability to remove ice, the specific topography of the "gates"

(narrow areas that constrict the flow of ice), and the specific

location of grounding lines (land on which marine ice sheets

rest)._^0/  These factors will determine the speed of discharges.

Unfortunately, such studies have not yet been made for deglaciation

in the next century.

     Method Used to Estimate Snow and Ice Transfers from Land
     to Sea

     In the absence of appropriate studies of the various ice

fields, another approach had to be used that was much less

direct:

     o  A range of historic sea level rise estimates was
        gathered from the literature.

     o  An estimate of the historical sea level rise
        attributable to thermal expansion of the oceans was
        obtained from the literature.

     o  High and low ratios of ice and snow contributions to
        thermal expansion were computed using different estimates
        of the historical sea level rise with the single estimate
        of past thermal expansion.

     o  These ratios were assumed to remain constant in the future
        (implying that snow and ice contributions will proceed
        in marginal steps and that deglaciation, when averaged
        across all ice sheets, will also be a proportional
        phenomenon).

-------
                             - 31 -








     Estimates of the Last Century's Sea Level Rise




     In the last century, measurements of tidal heights have




been collected in harbors around the world.   On the basis of these




measurements, several researchers have concluded that worldwide




sea level has been rising.  (See Table 3-2 on the next page.)




     Differences between sea level rise estimates can be attri-




buted to several factors that make precise interpretation of the




data difficult.  Tidal gauges are influenced by local conditions




that do not influence worldwide sea level, such as river flow,




weather, and emergence or submergence of land.  Furthermore,




they are not distributed uniformly, and large parts of the




oceans are unmeasured.




     To overcome these problems, the various researchers employed




different approaches.  Some researchers averaged all available




stations.  Others chose a few stations in each typical geographic




zone and assumed them to be "representative."  At least one




group of researchers also attempted to factor out local tectonic




influences.^/  Despite the differences, however, the estimates




of sea level rise have been remarkably similar.  Most of the



researchers have concluded that worldwide sea level has risen




between 10 and 15 centimeters in the last century.22/

-------
                              -32-
                           TABLE 3-2

               ESTIMATES OF GLOBAL SEA LEVEL RISE

                        (cm per century)
Author
Thorarinsson (1940)

Gutenberg (1941)

Kuenen (1950)

Lisitzin (1958)

Wexler (1961)

Fairbridge and Krebs (1962)

Hicks (1978)

Emery (1980)

Gornitz et al (1982)

Barnett (1983)
Estimate

>  5 cm

  11 + 8 cm

  12 to 14 cm

  11.2 +_ 3.6 cm

  11.8 cm

  12 cm

  15 cm (U.S. only)

  30 cm

  12 cm (10 cm excluding
           long-term trend)
  15 cm
Sources:  Adopted from Barnett (1983) and Hicks (1978)

-------
                             - 33 -


     Determining the Ratios

     Using available estimates on past temperatures and the

rates of heat absorption in the oceans, Gornitz et al. estimated

past sea level rise due to thermal expansion to be 4 to 5 cm

the last century.23/

     o  For the low scenario, a 10-centimeter estimate of
        historicalsea level rise was used, thus implying a
        one-to-one ratio of the contribution of snow and ice
        to thermal expansion.

     o  For the high scenario, the higher sea level rise
        estimate of 15 cm was used, thus implying a ratio
        of two-to-one.

     Deficiencies in Our Estimates of Snow and Ice Contribution

     Although the GISS 3-D experiments yield a similar magnitude

for the rate of sea level rise as the ratio method, we have no

illusions about the adequacy of these projections.  If estimates

based on process models of deglaciation had been available, we

would have used them.   The ratios depend on estimates of change

which are themselves subject to mis-estimation.  Futhermore,

the physical basis for extrapolating the historical ratio

into the future is weak at best.   Past "associations" may

not continue in the face of much larger temperature increases.

     To remedy this situation, EPA and NASA have assembled

a team of glaciologists, oceanographers, and climatologists,

who, with limited funding, will use "process models" and

judgment to estimate a range for  possible meltwater runoff

-------
                             - 34 -


and deglaciation.  A comprehensive well-funded effort, however,

is still not on the research agenda of any federal agency.


CHANGES IN VOLCANIC AEROSOLS AND SOLAR IRRADIATION COULD
INFLUENCE CLIMATE

     From decade to decade solar irradiation and volcanic

aerosols in the atmosphere may vary.  An increase in aerosols

can have a cooling effect, while an increase in solar irradiation

will have a warming effect.  In coming decades it is likely

that there will be fluctuations for both factors, but there is

no reason to expect a consistent long-range trend.  Nevertheless,

to test tne possible influence of a strong shift in these

factors, these changes were examined:

     o  For the minimum case, we assumed high volcanic
        activity and a reduction in solar radiation.  A level
        of optical thickness was chosen that was five times
        the historical average over the last 80 years.24/
        A linear trend equal to a 0.5 percent reduction in
        solar radiation by 2100 was assumed.25/

     o  For the maximum case, we assumed solar irradiation
        increased by a linear trend to a 0.5 percent increase
        by 2100, with no change in volcanic activity.

     o  For the high volcanic case, we assumed high volcanic
        activity, but no change in the solar constant.


These and other special-case scenarios are reported in

Appendix A.  They suggest that the greenhouse effect is not

likely to be overwhelmed by volcanoes or changes in solar

irradiation.

-------
                              -  35  -
                       END NOTES  CHAPTER 3
      The figure below shows a  schematic  relationship of the
      factors considered in estimating  the sea level rise:
                           BASIS FOR SCENARIOS
POPULATION
GROWTH
PRODUCTIVITY
GROWTH
COST OF
ENERGY
TECHNOLOGIES

ENERGY
USE PER
UNIT OUTPUT
ATMOSPHERIC
GROWTH TRACE
GASES



1
ATMOSPHERIC
co2


CLI
SOLAR IRRADIATION


MATE
RESPONSE



VOLCANIC
AEROSOLS
I
THERMAL SENSITIVITY OF CLIMATE
SYSTEM TO CHANGES IN GREENHOUSE
GASES AND OTHER FORCIf
IGS


COEFFICIENTS
OF HEAT
DIFFUSION


THERMAL
EXPANSION
OF OCEAN'S
VOLUME
1



"ICE/SNOW-


WATER
MASS ADDED
TO OCEANS




LEVEL RISE

ESTIMATED
RATIO OF
"ICE/SNOW^
TO THERMAL
EXPANSION

                             SEA LEVEL RISE
                For wch factor or r.lrtorhlp high ml tow
                                  wn itovrtopM imMg th. publW.l Hwratur.
2.
3.
4.
5.
Keyfitz, Nathan,  et al.,  1983.  Global Population  (1975-2075)
and Labor  Force  (1975-2050).  Oak Ridge, TN: Oak Ridge
Associated Universities,  Institute for Energy Analysis.

Edmonds, Jae,  and John Reilly, 1982b.  "Global  energy and
C02 to the year  2050." Washington, D.C.: Oak Ridge  Asso-
ciated Universities.

Emanuel, W. R.,  and Killough, G. G., computer tape  provided
with 17-layer  ocean model.   Oak Ridge, TN: Oak  Ridge
National Laboratories.

Siegenthaler,  Ulrich,  1983.  "Uptake of excess C02 by  an
outcrop diffusion model of  the ocean."  Journal of
Geophysical Research.  88:06:3599-608.

-------
                             - 36 -
6.    Broecker,  Wallace Smith,  and Tsung-Hung Peng,  1982.
     Tracers in the Sea.   Palisades,  N.Y.:  Lament - Doherty
     Geological Observatory,  Columbia University.

7.    Ibid.

8.    Gibbs,  Michael,  Current  and Future CFG Production and Use,
     Washington, U.C.: ICF,  1983.

9.    Weiss,  R.F., Keeling,  C.D., and  Craig, H.,  "The Determi-
     nation  of  Tropospheric  Nitrous Oxide," Journal of
     Geophysical Research,  Vol.  86, No. 68, August 20, 1981,
     pp.  7197-7202.

10.   Rasmussen, R.A.,  Khalil,  M.A.K., "Increase  in the
     Concentration of  Atmospheric Methane"  Atmospheric
     Environment, Vol. 15,  No.  5, 1981, pp. 883-886.

11.   Lacis,  A., personal  communication, October,  1983.

12.   Cloud responses  would  affect the total amplification
     because cloud cover,  heights, and their optical properties
     (the amount of sunlight  they reflect)  could  influence
     and  change the radiation balance and the earth's
     temperature positively or negatively.

13.   Hansen, James E., et  al.  1981.,  "Climate impact of increasing
     atmospheric carbon dioxide." Science.  213:4511:957-66.
     The  equation was  modified by A.  Lacis  to allow the trace
     gases to be considered.   A box diffusion model portrays
     the  ocean  as a column  of  water and treats the movement of
     heat as a  passive tracer.   The GISS group adpoted the
     model from Oeschger,  H.,  et al., 1975.  Tellus. 27:168.

14.   Broecker,  Wallace Smith,  Tsung-Hung Peng, and R. Engh, 1980.
     "Modeling  the carbon  system," Radiocarbon.  22:3:565:-98.

15.   For  example, an  article  in Newsweek, ("Is Antarctica
     Shrinking", October  5,  1981) focused solely  on the rise
     in sea  level that might  be caused by ice transfers,
     completely ignoring  thermal expansion.

16.   Manabe, Sykuro,  and  Richard T. Wetherald, 1975.  "The
     effects of doubling  the  CO2 concentration on the climate
     of a general circulation model." Journal of  the Atmospheric
     Sciences.   32:1:3.

     Hansen, James, E., et.  al., 1983. "Efficient three-dimensional
     global  models for climate studies: models I  and II."
     Monthly Weather  Review.  111:4:609:62.

-------
                             - 37 -
     Washington, W.M. and D.L. Williamson, 1977. "A description
     of the NCAR global circulation models in methods of
     computational physics," in General Circulation Models
     of the Atmosphere, J. Chang, ed.   New York:  Academic
     Press, 17:111-172

17.  Russell, G.; see Appendix C of this report.

18.  Mercer, J.H., 1978.  "West Antarctica ice sheet and CC>2
     greenhouse effect:  a threat of disaster." Nature.
     271:5643:321.

19.  Bentley, Charles R., 1983. "West Antarctic ice sheet:
     diagnosis and prognosis," in Proceedings; Carbon Dioxide
     Research Conference; Carbon Dioxide, Science and Consensus
     1983,  Washington, DC:  Department of Energy. U.S. CONF-820970

     Hughes, T., 1983. "The stability of the west Antarctic ice
     sheet:  what will happen," in Proceedings;  Carbon Dioxide
     Research Conference: Carbon Dioxide, Science and Consensus
     1983.   Washington, DC: U.S. Department of Energy. CONF-820970,

20.  Ibid.

21.  Gornitz, Vivian, S. Lebedeff, and J. Hansen, 1982.  "Global
     sea level trend in the past century." Science.   215:26:1611-4

22.  Barnett, T.P., 1983.  "Global sea level: estimating and
     explaining apparent changes," in Coastal Zone '83, Orville
     T. Magoon, editor. New York: American Society of Civil
     Engineers.  3:2777-84.

23.  Gornitz, V., S. Lebedeff, and J. Hansen, op. cit.

24.  Lamb,  H.H.,  1970.   "Volcanic dust in the atmosphere."
     Philosophical Transactions of the Royal Society.  London
     Series A, 255:425.

25.  Sofia, S., and A.S. Endal, 1982. "Solar variability."
     Reviews of Space Physics.

-------
                             - 38 -


                           CHAPTER 4

              SEA LEVEL SCENARIOS TO THE YEAR 2100


     This chapter presents our estimates of sea level rise, using

the methods described in the previous chapter.  It also discusses

alternative approaches for pro3ecting sea level rise that yield

similar estimates, increasing our confidence in these results.

     Table 4-1 presents the four major scenarios.   The low and

high scenarios use low and high assumptions, respectively, for

each of the factors influencing sea level rise.  The two mid-range

scenarios use the medium estimate of sea level rise attributable

to thermal expansion.  However, given the greater uncertainty

about snow and ice contributions to sea level rise, the mid-range

high and mid-range low use the two-to-one and one-to-one

assumptions for glacial contributions to sea level rise,

respectively.



                           TABLE 4.1

               SCENARIOS OF FUTURE SEA LEVEL RISE
                         (centimeters)

                                    Year

                 2000      2025
Scenario

High

Mid-range high

Mid-range low

Low

Current Trends  2.0-3.0   4.5-6.8  7.0-10.5  9.5-14.3  12.0-18.0
2000
17.1
13.2
8.8
4.8
2025
54.9
39.3
26.2
13.0
2050
116.7
78.9
52.6
23.8
2075
211.5
136.8
91.2
38.0
2100
345.0
216.6
144.4
56.2

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                             - 39 -






     We believe that the actual rate of sea level rise is more




likely to fall between the two mid-range estimates than outside




of them.   Because the high and low scenarios employ more extreme




assumptions, neither is likely to occur.  However, the possibility




can not be ruled out.






SEA LEVEL RISE WILL ACCELERATE UNDER ALL ASSUMPTIONS




     Even in the low scenario, sea level will rise twice as




fast as its historical rate in the next 20 years, and from




2000 to 2025, at three times the historical rate.  In the high




scenario, the sea will rise about ten times its historical




rate from 1980 to 2025.  Over the last quarter of the 21st




century,  the high scenario predicts the sea to rise at over 40




times the historical rate.




     The  mid-range scenarios predict that from 1980 to 2000,




sea level will rise almost as much as it has in the last century.




Given local trends on much of the East and Gulf Coasts of the




United States, shoreline retreat in the next 20 years could




be one-half that of the past century.  In the following 25 years,



worldwide sea level would rise at about eight times the historical




rate, creating much greater erosion and flooding problems.




Thus, in  the next four decades (within the lifetimes of many



projects  now under design) the sea is likely to rise twice as




much as it has in the last century.






AN ALTERNATIVE METHOD PRODUCES SIMILAR ESTIMATES OF SEA LEVEL RISE




     To cross check our projections, we estimated sea level




changes by another method: extrapolating past associations

-------
                             - 40 -



between temperature and sea level.  Sea level rise in the last

century has been estimated at 10 to 15 cm (4 to 6 inches).

The surface temperature rise for the same period has been

estimated at 0.4C.  Thus, the ratio of sea level rise to

temperature is somewhere between 25 and 37 cm for each degree.

Including the effects of trace gases, global warming should be

equivalent to at least a quadrupling of C02 by 2100, which

would raise surface air temperatures by 3.0C to 9.0 (based

on the National Academy of Sciences' range for climate

sensitivity, ignoring delays caused by the heat absorbing-

capacities of the oceans).  Using the 25 cm to 37 cm ratio for

the 3C to 9C range yields sea level rises of 75 cm to 333 cm,

These estimates are in line with those produced by our more

elaborate approach.

     One other result is worth noting.  Using a time series

regression, Chylek and Kellogg estimated a 10 cm to 25 cm sea

level rise per 1C temperature rise.  For a temperature rise

of the magnitude projected, here, their result is consistent

with a sea level rise of 30 cm to 225 cm.^/


                     END NOTES TO CHAPTER 4

1.   Chylek, Peter, and William Kellogg, 1982. "The Sea Level
     Climate Connection," unpublished paper, National Center
     for Atmospheric Research, Boulder, Colorado.

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                             - 41 -


                           CHAPTER 5

                   IMPACTS OF SEA LEVEL RISE


     The objective of this report is to project sea level

rise, not to evaluate its impacts.  Nevertheless/ because our

reason for estimating sea level rise is to help decision makers

and professionals anticipate its effects and evaluate its

importance, we provide a brief discussion of the impacts in

this section.


THE MOST SIGNIFICANT DIRECT IMPACTS WILL BE SHORELINE RETREAT,
INCREASED FLOODING, AND SALT INTRUSION

     Sea level rise will have three major types of physical

effects: shoreline retreat,  increased flooding, and landward

movement of saltwater.  Shorelines will retreat because very

low land will be innundated  and other land along the shore

will erode.  For example, a  thirty centimeter (one foot) rise

in sea level would erode most sandy beaches along the U.S.

Atlantic and Gulf Coasts at  least thirty meters (one hundred

feet).

     Even the historical sea level rise trend may be causing

significant erosion._/  Most shorelines are maintained by the

balance between sediment eroded by storms and sediment deposited

back on the beach by waves during calm periods.  However, a

rise in sea level allows storm waves to strike and erode the

beach farther inland, and makes calm waves less effective at

"dredging" sand from the ocean floor and redepositing it onto

the beach.

     The Bruun Rule (illustrated by Figure 5-l)^/, a method

-------
                             - 42 -



for quantifying the erosion impact, has been validated by

field tests on the Great Lakes.jV  The shore maintains the

equilibrium profile shown by the solid line.  When sea level

rises, this profile must also rise, which requires additional

sediment equal to b'.   Unless sediment is transported into the

area by currents or by mechanical dredges, ocean waves will

provide the sediment by eroding enough sand from the upper

portion of the beach to equal _b, producing the new profile

shown by the dotted line.  Applications of this theory have

concluded that a rise in sea level of one centimeter can cause

the shore to erode between one hundred and one thousand

centimeters on the Atlantic and Gulf coasts of the United States,

                           FIGURE 5-1
                          BRUUN RULE
                  BEACH

                 ,  x     SEA LEVEL   INITIAL SEA LEVEL
                 \b\  XAFTER RISE  /	\
     BOTTOM PROFILE/
     AFTER SEA
     LEVEL RISE
INITIAL BOTTOM
   PROFILE
                                    LIMITING DEPTH 
                                    BETWEEN PREDOMINANT
                                    NEARSHORE AND
                                    OFFSHORE MATERIAL
      SHORE EROSION FOLLOWING A RISE IN SEA LEVEL ACCORDING TO
      THE BRUNN RULE (AFTER SCHWARTZ 1967) "THE BRUNN THEORY OF
      SEA LEVEL RISE AS A CAUSE OF SHORE EROSION, " ADOPTED FROM
      THE JOURNAL OF GEOLOGY, 75, 76-92.

-------
                             - 43 -






     Low-lying areas not lost to a rising sea will experience




increased flooding, for a number of reasons.  The higher sea




level will provide a higher base on which storm surges can




build.  Beach erosion and deeper water may allow large waves




to strike further inland.  Finally, higher water tables will




decrease the land's drainage capacity, increasing runoff




during storms.




     Sea level rise will also cause salt water to move landward,




intruding into groundwaters, rivers, and estuaries.  In some




rivers, salt may move upstream tens of kilometers.  This effect




may alter local availability of fresh water and alter ecosystems




in some areas.^/






IMPACTS WILL DEPEND ON HOW PEOPLE ANTICIPATE SEA LEVEL RISE




     Economic and environmental impacts will depend on how well




people anticipate and plan for the physical changes associated




with sea level rise.  As busineses, governments, and individuals




make decisions in coastal and low-lying areas, they have the




opportunity to adjust to sea level rise before it occurs, which




will decrease the eventual impacts of erosion, flooding, and




saltwater intrusion.




     Many decisions have outcomes that last long enough to be



affected by sea level rise, e.g., where to locate roads,




wastewater treatment plants, and chemical and nuclear waste




storage facilities,  (See Table 5-1.)  A coastal highway may




determine development patterns long after the pavement and the




structures along the road have been replaced.  Similarly, although




a nuclear power plant built today may only be designed to operate

-------
                                   -44-


                            TABLE 5-1

CATEGORIES OF DECISIONS SEA LEVEL RISE WILL INFLUENCE


  LOCATIONAL DECISIONS


        WHERE TO PUT PRIVATE DEVELOPMENT AND REDEVELOPMENT

         -HOUSING
         - FACTORIES
         - RESORTS
         - ENERGY FACILITIES
         - HAZARDOUS WASTE SITES

        PUBLIC DEVELOPMENT DECISIONS-ROADS
         - UTILITIES
         - PORT INFRASTRUCTURES
         - PARKS
         - BRIDGES

        PURCHASE OF LANDS FOR CONSERVATION


  STRUCTURAL AND SITE DESIGN DECISIONS
        HOW TO BUILD FACILITIES

         - THEIR MOVABLILITY
         - SITE CONTOURING
         - CONSTRUCTION TYPE AND QUALITY
         - PLANNED LIFETIME OF STRUCTURE

        R&D ON HOW TO IMPROVE OPTIONS

         - SUCH AS MAKING STRUCTURES MORE "SEA LEVEL RESISTANT"
         - MAKING STRUCTURES MOVE MOVABLE

        HOW TO MAKE LOW-COST DESIGN CHANGES TO REDUCE ADVERSE EFFECTS


  PROTECTIVE MEASURES AGAINST FLOODS AND EROSION
        PROTECTIVE FACILITIES SUCH AS SEAWALLS

         - HEIGHT
         - TYPE
         - FOUNDATION SIZE (SO THEY CAN BE EXPANDED LATER)

        BEACH NOURISHMENT DECISIONS

        VEGETATION PLANTING AND MAINTENANCE DECISIONS

        RIVER CHANNELING AND RECHANNELING DECISIONS

        LAND ACQUISITION AND SET ASIDE FOR PUBLIC AND PRIVATE WORKS
         FOR FUTURE PROTECTION

        LOCAL ZONING AND OTHER LAND-USE CONTROLS TO REDUCE DEVELOPMENT
         IN WRONG AREAS

        FLOOD PROTECTION REQUIREMENTS FOR HAZARDOUS FACILITIES

   DECISIONS ABOUT FLOOD MITIGATION PLANNING
        EVACUATION PLANS

        POST-DISASTER PLANS

        INSURANCE POLICIES, SUBSIDIES AND COSTS

-------
                             - 45 -


for 30 years, its location may become the only available site

for power generation in a given region for hundreds of years.

     The wide range of sea level rise scenarios makes planning

more difficult than it would be if we were certain about a

particular forecast.  Nevertheless, prudence demands that

decision makers plan for at least the low sea level rise scenario,

which would change many decisions.  For other decisions, the

low scenario presents few risks, but the high scenario would

pose major problems.  In such cases risk analysis can be used to

balance the benefits and costs of various planning options for

for each sea level rise scenario.


QUANTITATIVE ESTIMATES SHOW LARGE PHYSICAL EFFECTS
AND ECOLMOMIC IMPACTS FROM ANTICIPATED SEA LEVEL RISE

     Few studies of the physical consequences of sea level

rise have been undertaken.  Schneider and Chen concluded that

a 4.7-meter (15-foot) rise in sea level would innundate over

one-fourth of Louisiana and Florida, as well as one-eighth of

Delaware, Maryland, and the District of Columbia.5/

     EPA has funded case studies on the impacts of sea level

rise for the areas around Charleston, South Carolina and

Galveston, Texas.  Detailed results of these studies are

available in Sea Level Rise Conference Document.6/ A forth-

coming book entitled Sea Level Rise to the Year 2100, will

contain papers by the same researchers, as well as the reactions

of coastal decision makers who attended that conference.^/

-------
                             - 46 -






     Both case studies found that sea level rise will have




significant impacts.  Research Planning Institute concluded




that a 1.5 meter (five foot) rise in sea level would innundate




one-quarter of Charleston if no additional bulkheads or seawalls



were constructed.^/  They also calculated that areas in




Charleston that are now flooded once every 100 years would be




flooded once every 10 years.  Leatherman concluded that a




1.5 meter rise would claim much less land around Galveston,




provided that the existing network of levees and seawalls were




maintained.^/  However, he estimated that such a rise would




double the area flooded every 15 years.  Because Galveston




is already vulnerable to storms, Gibbs concluded that the




resulting annual storm damage in this area would increase to




$105 million from $23 million._W




     Quantitative projections of the effects of sea level rise




on salinity in surfacewater and groundwater have only been made




in limited cases.  The Delaware River Basin Commission has




estimated the effects of historical sea level trends on salt




concentrations in the Delaware River./ it plans to examine



the effects of the scenarios reported here, which may threaten




aquifers recharged by the river and possibly Philadelphia's




current water intakes during droughts  However, no comprehensive




analyses have been undertaken of salinity intrusions from sea




level rise.

-------
                             - 47 -






   CURRENT AND FUTURE EFFORTS TO STUDY SEA LEVEL RISE IMPACTS



     The National Academy of Engineering's Marine Board plans




to assess the engineering implications of sea level rise. -*-2/




Port and coastal structures are designed for lifetimes of 100




years and possibly longer.  The Marine Board is interested




in determining whether the evidence of possible sea level rise




justifies designing structures to withstand such a rise.  It




also intends to determine whether the existing network of tidal




gauge stations is sufficient to detect a CO2~induced rise




in global sea level.   EPA is working with the Delaware River




Basin Commission to determine the impact of sea level rise on




drinking water.  Projects in Maryland, New Jersey, and New




York are being considered, and others are being sought, j-3/




     The prospect of  sea level rise of the magnitude estimated




in this study is so new, however, that much more basic research




and study needs to be done on its effects, the methods for




estimating them, and on the economic importance of anticipating




the rise.




     A variety of academic and professional disciplines need to



define research and action agendas for understanding and




preparing for sea level rise.  B'or example, planners should




review zoning standards and architects should review building




codes.   Coastal geologists should develop better means of




projecting erosion.  Paleo-sea-level researchers should consider




how their substantial body of knowledge can be used for

-------
                             - 48 -


understanding the response of the land to sea level change,

for validating climatic models, and for adjusting global sea

level estimates by regional influences.^/

     The need for additional research is further underscored

by EPA's pilot studies, which demonstrate that half the damages

can be prevented with adequate planning.  Ignoring this

opportunity could be very costly to society.  In the next

chapter, we discuss the research necessary to improve sea

level rise projections.  However, preparing for sea level rise

will also require a much better understanding of its effects.


                     END NOTES TO CHAPTER 5
1.   Pilkey, Orrin, et al., 1981.  Saving the American Beach;
     A Position Paper by Concerned Coastal Geologists.  Results
     of the Skidaway Institute of Oceanography Conference on
     America's Eroding Shoreline.  Savanah:  Skidaway Institute
     of Oceanography.

2.   Bruun, Per, 1962.  "Sea level rise as a cause of shore
     erosion." Journal of Waterways and Harbors Division.
     New York: American Society of Civil Engineers.  1:116-30.

     Schwartz, M.L. 1967.  "The Bruun theory of sea level rise
     as a cause of shore erosion."  Journal of Geology.  75:76-92,

3.   Hands, Edward B., 1980.  Prediction of Shore Retreat and
     Nearshore Profile Adjustments to Rising Water Levels on
     the Great Lakes, Technical^ Paper Number 80-7.  Fort
     Belvoir, VA:  US Army Corps of Engineers, Coastal
     Engineering Researcn Center.

     Weggel, J.R., 1979.  AMethod for Estimating Long-Term
     Erosion Rates from a Long-Term Rise in Water Level,
     Coastal Engineering Aid Number 79-2.  Fort. Belvoir, VA:
     U.S.  Army Corps of Engineers, Coastal Engineering Research
     Center.

-------
                             - 49 -
4.   Haskin, H.H., and Tweed, S.M., 1976.  Oyster Setting and
     Early Spat Survival at Critical Salinity Levels on Natural
     Seed Oyster Beds of Delaware Bay.  New Brunswick, NJ:
     Water Resources Research Institute, Rutgers University.

5.   Schneider, Stephen H. and Robert S. Chen, 1980.  "Carbon
     dioxide flooding:  physical factors and climatic impact,"
     Annual Review of Energy.  5:107-40.

6.   This Document is Available from EPA.

7.   Barth, Michael and James Titus, eds.  Sea Level Rise to The
     Year 2100. Stroudsburg, PA: Hutchinson Ross, (in press).

8.   Kana, Timothy w., et al., 1983.  "Shoreline changes due
     to various sea level rise scenarios," in Coastal Zone '83
     Orville T. Magoon, ed.  New York:  American Society of
     Civil Engineers.  3:2768-76.

     Kana, Timothy W., et al., "The Physical Impact of Sea Level
     in the Area of Charleston,  South Carolina," in Barth, Michael
     and James Titus, eds., op.  cit.

9.   Leatherman, Stephen, 1983.   "Geomorphic effects of projected
     sea level rise:  a case study of Galveston Bay, Texas,"
     in Coastal Zone '83, Orville T. Magoon, ed.  New York:
     American Society of Civil Engineers.  3:2890-901.

     Leatherman, Stephen, "Coastal Geomorphic Responses to
     Sea Level Rise: Galveston Bay, Texas," in Barth, Michael
     and James Titus, eds., op.  cit.

10.  Gibbs, Michael, 1983.  "Economic effects, and value of
     information on sea level rise," in Coastal Zone '83,
     Orville T. Magoon, ed.  New York:  American Society of
     Civil Engineers.  3:2754-67.

     Gibbs, Michael, "Economic Analysis of Sea Level Rise:
     Methods and Results," in Barth, Michael and James Titus,
     op. cit.

11.  Hull, C.H.J., and R.C. Tortoriello, 1979.  "Sea level
     trend and salinity in the Delaware estuary."  Staff paper.
     West Trenton:  Delaware River Basin Commission.

12.  Gallagher, Aurora, personal communication to James Titus,
     Marine Board, National Academy of Sciences, 2101
     Constitution Avenue, N.W.,  Washington, D.C. 20418.

-------
                             - 50 -
13.   Interested parties should contact:   James Titus.
     U.S.  EPA,  (PM-220) Washington,  D.C.  20460.

14.   Lisle,  L.D.,  1982.  "Annotated  bibliography of sea level
     changes along the Atlantic and  Gulf  coasts of North America."
     Shore and  Beach.   50:3.

     Shennan,  Ian, University of Durham,  personal communication
     with  John  S.  Hoffman

-------
                             - 51 -
                           CHAPTER 6

                   RESEARCH NEEDED TO IMPROVE
                   ESTIMATES OF SEA LEVEL RISE
     Little research has been conducted to estimate future sea

level rise.  Improving the scenarios developed in this report

will require appropriate research and accurate monitoring of

the underlying physical systems.  Although some of the scientific

problems may resist solution, a larger and better-focused

research effort could solve most of them in time for the resulting

information to be useful to coastal decision makers.  A key

determinant of progress will be the priority society attaches

to this research.

     This chapter examines the sources of variation in the

estimates of sea level rise, to help identify the most promising

opportunities for additional research.  It also discusses

principles for managing this research.


MONITORING SEA LEVEL WILL NOT BE SUFFICIENT

     The low and high scenarios differ by a factor of six.

This range makes it difficult for managers to decide how to

reduce the adverse impacts of sea level rise.  A "wait and see"

approach would eventually reveal which scenario is most accurate.

But because most forthcoming decisions cannot be postponed

the several decades that this might require, these managers

need a smaller uncertainty range.  This can be achieved by

reducing the uncertainties surrounding the individual assumptions

that must be made to project sea level rise.

-------
                             - 52 -


     Interpreting the observed sea level rise will be difficult.

Many factors that cause short-term variations in global

temperature and sea level have not been modeled, including the

internal dynamics of the climate system, changes in ocean

circulation, and year-to-year fluctuations in volcanic activity.

Thus, if the sea rises 9 to 13 centimeters by 2000 (the most

probable range), then it will be difficult to determine the

amount of this rise caused by the greenhouse warming, as

opposed to temporary fluctuations caused by other factors,

unless better monitoring and research is undertaken.   It will

be even more difficult to determine the percentage of the rise

that should be attributed to thermal expansion versus glacial

contribution.  Better research and monitioring could  help

ensure that our ability to forecast sea level rise improves as

additional data becomes available.


UNDERSTANDING THE SOURCES OF DIFFERENCES BETWEEN SCENARIOS CAN
HELP FOCUS RESEARCH PRIORITIES

     The estimates of thermal expansion vary by a factor of four.

However, the greatest source of uncertainty is the rate of

transfer of snow and ice from land to sea, which varies by a

factor of eight between the low and high scenarios.  Unfortunately,

there has been insufficient funding of coordinated work between

glaciologists, climate modelers, and Southern Hemisphere

oceanographers to estimate this important source of sea level

rise.

     Examining the sources of uncertainty is a first step

toward developing research priorities.  Figure 6-1 shows the

-------
                             - 53 -






contribution of each major factor to the current uncertainty




of sea level rise from thermal expansion, using the low scenario




as a baseline.   Assumptions were changed one-at-a-time from



low to high for each factor.  The first four factors (CC>2



emissions, chlorofluorocarbons, nitrous oxide, and methane)




were approximately additive in their effects.  Because the



other factors were not, changing them in a different order




would change these estimates somewhat.  Nevertheless, this




figure conveys  the relative importance of the uncertainties



for each of the various factors in 25-year time spans.



     This figure reveals some important insights for setting




research priorities.  The best way to improve estimates of sea



level rise to the year 2025 would be to improve estimates of




temperature (climate) sensitivity, and next, the concentrations




of the trace gases.   In the longer term, the level of CC>2 becomes



quite important.



     The atmospheric fraction airborne for CC>2 and diffusivity



do not appear to be  the major sources of uncertainty.  It is



possible that increasing temperatures may stratify the ocean,



and increase fraction airborne and decrease diffusivity beyond



the ranges of our assumptions.  However, although these effects



would both raise atmospheric temperatures, their effects on sea



level rise would tend to offset one another.




     Appendix A shows that in the long run, the impact of



extreme and unexpected forms of natural variation (volcanoes



and solar radiation) are unlikely to be important, except in




the early stages when they could mask the overall trend.

-------
                                 -  54 -


Unless these factors are  carefully monitored, their variability

could reduce the  ability  of scientists to  understand the

other factors.




                               Figure 6-1

            RELATIVE CONTRIBUTION OF FACTORS TO THE DIFFERENCE
          IN SEA LEVEL RISE BETWEEN THE HIGH AND LOW SCENARIOS
                                                                  C02
                                                                Fraction
                                                                Airborne
QC
_C
05
O



I
Q
     o>
     Q_
         30 -
         10-
                                                                Thermal
                                                                Sensitivity
                                                                Heat
                                                                Diffusivity
                                                                CFCs
                                                            C0?
                                                            Emissions
             2000
                    2025
2050
2075
2100
     NOTE: Factors were evaluated in the order that they appear starting at the top.

-------
                             - 55 -


OPPORTUNITIES EXIST FOR MORE RESEARCH

     The greatest needs are:

     o  projecting the transfer of ice and snow from land
        to sea;

     o  estimating the atmospheric changes in the trace gases
        methane, nitrous oxide, and the chlorofluorocarbons;
        and

     o  estimating the sensitivity of the climatic system to
        atmospheric and other changes.

     As discussed earlier, in response to these findings, EPA,

in cooperation with NASA, has already initiated work to improve

our understanding of snow and ice melting, oceanic warming

around Antarctica, and glacial ice discharge.  An inter-

disciplinary team of scientists from the Goddard Institute

for Space Studies (GISS), NASA, and Lamont Doherty Geological

Observatory has formed to improve the scenarios.  They will

use output from the GISS general circulation models; ice sheet/ice

shelf process models; estimates of oceanic changes provided by

a southern hemisphere oceanographer; and a thorough literature

review of ice fields.

     In early 1984, another scenario report will be issued

that incorporates the results of this project and refines the

thermal expansion model so that it reflects a geographically

disaggregated absorbtion of heat by the world's oceans.  That

effort should increase the reliability of the scenarios somewhat.

In the longer term, however, more precise and reliable estimates

of sea level rise will become available only if efforts are

made to improve our underlying knowledge of the relevant

natural systems.

-------
                             - 56 -



     Several projects need to be undertaken to improve the

basic scientific understanding of glacial processes:

     o  Better Monitoring of the Ice Packs

        The amount of ice and snow in all ice fields must be
        carefully tracked, probably with a combination of
        observations from space and land.

     o  Experiments with Ice Sheets

        Basic aspects of ice processes must be studied,
        especially those that relate friction and ice
        movement and the influence of warming and refreezing
        on the forces that determine ice movement.

     o  BetterTopographical Surveys

        Land under ice sheets that could affect the rate
        of discharge must be mapped better.

     o  Parametric Studies with ice Models

        Studies that consider different interpretations
        of ice processes and environmental conditions need
        to be conducted with ice sheet and ice -shelf models.

     o  Improvements in Polar Climatology, Sea Ice, and
        Oceanography in Climatic Models

        Representations of the climatic processes,  melting
        of sea ice, and the oceanographic processes need to
        be improved, with interdisciplinary teams contributing
        to ensure that general circulation models treat these
        areas realistically.

    A major effort should be undertaken to narrow the uncertain-

ties regarding trace gases.

     o  Develop Better Estimates of Sources and Sinks

        Research has been insufficient to even determine
        the origins and fates of these gases

     o  Develop a Better Understanding of Atmospheric Chemistry

        The interactions of these gases in the atmosphere
        greatly influence their abundance, and should be better
        assessed.

-------
                             - 57 -


     o  Integrate Atmospheric Chemistry and Climatic
        Modeling

        Because atmospheric chemistry depends on temperatures
        and atmospheric mixing, atmospheric chemists and climate
        modelers must work in closer contact with each other.

     Knowledge of the speed of climatic change and the sensi-

tivity of the climatic system to changes in atmospheric composi-

tion can be greatly enhanced in several ways.

     o  Develop a Better Representation of the Oceans

        Dynamic ocean models can be integrated into general
        circulation models in realistic ways in the next 10
        years only if a major, well-funded effort is undertaken.
        This is critical to producing a more valid geographical
        distribution of precipitation and temperature changes
        needed to estimate ice and snow changes.

     o   Improve Data on Clouds

         Better observational data, a better theoretical under-
         standing, and a better computational representation
         of cloud processes can reduce tne uncertainty of the
         effect that clouds have on thermal sensitivity.

     o   Expand Computing Capability

         The acquisition and use of appropriately sized computers
         would allow more experiments, with different
         representations of various processes, to be run in
         general circulation models and also provide greater
         geographical resolution.  These efforts would allow
         quantification of the uncertainties in regional
         precipitation, which would considerably improve estimates
         of ice melting and snowfall.

     Sufficient personnel and resources are available to sustain

present efforts.  Over the longer term, however, progress will

require training new people.  While not particularly costly,

this process takes time.  Delaying its start would diminish

society's ability to accelerate research later.

-------
                             - 58 -
RESEARCH CAN BE MANAGED MORE EFFECTIVELY

     Research to improve estimates of sea level rise should

have three primary objectives:

     o  Establish interdisciplinary Teams of Sufficient Size

        Progress will be impeded if interdisciplinary teams
        are not developed and brought to work together on a
        long-term basis.  They must be large enough to address
        difficult long-term problems.

     o  Provide Long-Term and Secure Financial Support

        Interaisciplinary scientific teams will not evolve
        unless financial support is secure.   The development
        and maturation of research efforts depends on a steady
        source of funding.   These teams should be directed by
        eminent scientists.

     o  Develop Long-Term and Geographically Extensive Data
        Sets

        Efforts to collect  data must ensure that geographically
        extensive data sets are collected over long periods of
        time without interruptions.  The greater the extent
        and detail of the data, the more scientists can test
        their models for realism.

     Although success in scientific research cannot be guaranteed,

it can easily be thwarted by failing to develop the conditions

that make it possible.  The interdisciplinary nature of projecting

sea level rise makes management of research a particularly

important part of ensuring  progress.  The opportunity exists;

the decision facing society is whether or not to employ the

resources needed to meet this challenge.

-------
                               -59-
                            APPENDIX A

      SUMMARY OF SEA LEVEL RISE SCENARIOS INCLUDING SPECIAL
             CASES OF INCREASED VOLCANIC ACTIVITY AND
                    CHANGES IN SOLAR RADIATION
The abbreviations used in the following tables are explained below:

CO2 Scenario

     no growth -- constant (1975) emissions
     low growth  low (1.674 %) annual growth in emissions
     medium growth -- medium (2.074 %) annual growth in emissions
     high growth  high (2.345 %) annual growth in emissions

Thermal Sensitivity (Te)
     low  1.5C per doubling of CO2
     medium  3.0C per doubling of CO2
     high  4.5C per doubling of CO2
CH4 Scenarios
     no growth -- constant 1980 concentrations
     vl (very low growth)  0.5 % annual compound growth
     Ig (low growth) -- 1.0 % annual compound growth
     med (medium growth)  1.5 % annual compound growth
     hg (high growth) -- 2.0 % annual compound growth
     vh (very high growth)  2.5 % annual compound growth
N?0 Scenarios
     no growth -- constant 1980 atmospheric concentrations
     vl (very low growth)   0.1 % annual compound growth
     Ig (low growth)  0.2 % annual compound growth
     med (medium growth) -- 0.45 % annaul compound growth
     hg (high growth)  0.70 % annual compound growth
     vh (very high growth)  0.90 % annual compound growth


CFC Scenarios

     no growth -- constant 1980 emissions
     Ig (low growth)  1.8 million kg annual growth to 2020
     med (medium growth) -- 6.4 million kg annual growth to 2020
     hg (high growth)  9.8 million kg annual growth to 2020
     vg (very high growth)  11.6 million kg annual growth to 2100

All Scenarios assume that  emissions are constant after 2020 and that
the half-lives of CF2Cl2 (CFC-12)  and CFC13 (CFC-11) are 120
and 60 years (i.e., "lifetimes" are 150 and 75 years) respectively.

-------
                                   -60-
Volcanic Activity

     average -- Historical average optical depth value of .007
     high -- optical depth of .037 (average of highest two decades
             in last century. Both values are dimensionless;  see
             Appendix B)

Solar Luminosity

     average -- no net change in historical luminosity
     low -- Linear decrease from historical average to 0.5 %  less
            in 2100
     high -- Linear increase from historical average to 0.5%  more
            in 2100
Diffusivity Coefficient (k)

     very low  0.20 cm2/sec
     low  1.18 cm2/sec
     medium  1.54 cm^/sec
     high  1.9 cm2/sec
     very high  4.0 cm^/sec


CO? Retention (Fraction Airborne)

     ORNL  estimates from the ORNL carbon cycle model (.6 to .8)
     low --  a constant traction of 0.53

-------
                                                             -61-
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-------
                                        -62-


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-------
                              - 63 -
                            APPENDIX B

           MODELS, ANALYTICAL METHODS, AND ASSUMPTIONS
       USED FOR ESTIMATING THE SCENARIOS OF SEA LEVEL RISE
     Estimating the sea level rise produced by the temperature

increases that will be associated with rises in atmospheric

concentrations of C02 and other greenhouse gases required

integrating a variety of data, assumptions, and physical and

behavioral relationships (see Figure B-l).  For this integra-

tion, three models were used in this study.  The first is a world

energy and C02 emission model obtained from the Institute for

Energy Analysis (IEA) of the Oak Ridge Associated Universities.

The second is a regression equation that simplifies a one-dimen-

sional radiative/convective atmospheric temperature model obtained

from Dr. James Hansen of the Goddard Institute for Space Studies

(GISS).  This model also represents heat flux into the ocean and

computes sea level rise from thermal expansion of the ocean

layers.  The third, used in only some scenarios, is a global

carbon cycle model obtained from Dr. William Emanuel of the

Environmental Sciences Division, of the Oak Ridge National

Laboratory (ORNL).

     All three models were received from their developers in the

form of FORTRAN source programs and were installed on the EPA

computer located in North Carolina.  Throughout this appendix,

the models will be referenced as the IEA, GISS, and ORNL models.

-------
                                FIGURE  B-1

     KEY COMPONENTS OF THE ANALYTICAL  METHODOLOGY
POPULATION
  GROWTH
ASSUMPTIONS
       ENERGY COST
       ASSUMPTIONS
                             IEA ENERGY/CO2 MODEL

                           ENERGY - C02 EMISSION RELATIONSHIPS

                           ENERGY SUPPLY FUNCTIONS

                           ENERGY DEMAND FUNCTIONS
PRODUCTIVITY
  CHANGES
ASSUMPTIONS
                                FOSSIL FUEL CARBON
                                EMISSIONS OVER TIME
      NATURALC02SOURCES

      C02 SINKS
      FLOWS BETWEEN SOURCES
       AND SINKS
                                                             ASSUME CONSTANT
                                                             ATMOSPHERIC
                                                             C02RETENTION
ATMOSPHERIC CO
/ATMOSPHERIC (SEA SURFACE)
\TEMPERATURE OVER TIME
                  HEAT
                 DIFFUSION
                ASSUMPTIONS
                              SEA LEVEL THERMAL
                                 EXPANSION
C      ICE/SNOW
     ONTRIBUTION
          TOTAL SEA LEVEL
               RISE
                                                    TRACE GAS
                                                     GROWTH
                                                    ASSUMPTIONS
ASSUMPTIONS
ABOUT OTHER
FORCINGS
                       GISS MODEL
                                            ATMOSPHERIC C02 - TEMPERATURE
                                             RELATIONSHIPS
                                            OCEAN RESPONSES TO TEMPERATURE
                                        THERMAL
                 BOX DIFFUSION OCEAN MODEL - EXPANSION
                                        EQUATION

-------
                              - 65 -






     In addition to changing some of the parameters and operational




procedures of both the GISS and ORNL models, additional programs



were developed to provide simple interfaces between these two




models and to permit more rapid and extensive sensitivity analyses.




Separate sections of this appendix describe the individual models



and procedures for operating and combining them in the context




of this study, as well as the specific assumptions used to run




the scenarios.






THE ORGANIZING FRAMEWORK USED



     The assumptions, relationships, and models used to estimate




sea level rise are shown in Figure B-l.  The key variables are



described as primary inputs or outputs of the three models or



are subsumed in the internal structures of the models.




     As shown in Figure B-l, the three models are operated in



sequence.  The IEA model is first run to generate future energy



use and carbon emission scenarios.  The ORNL model (or an assumed




constant fraction of CO2 airborne) is next used to translate



fossil-fuel carbon emissions into atmospheric CO2 levels.  The



GISS model is finally employed to translate increases in C02



concentrations into atmospheric temperature increases and sea




level rise.  (The temperature of the atmosphere at the earth's



surface is assumed equal to the temperature of the ocean's top



layer.) The GISS model uses a variety of key assumptions as




inputs: trace gas growth, thermal sensitivity of the atmosphere,



and changes in other forcings.

-------
                              - 66 -






     The process of running the models is not perfectly sequen-




tial.  The ORNL and GISS models are coupled in an iterative




fashion for those analyses where the ORNL model is run. (This



is discussed below under the heading "Coupling the ORNL and GISS



Models.")   Endnote 1 presents the rationale for coupling ORNL




and GISS models and compares results using the two basic analytical



approaches.






MODEL DESCRIPTIONS



     Three models will be described: the IEA world energy model,



the ORNL carbon cycle model, and the GISS climate equation ocean



heat diffusion model.




The IEA Long-Term Global Model



     The IEA/ORAU model was developed by Jae Edmonds and John




Reilly at the Institute for Energy Analysis as an assessment



tool for policy analysis._2/  It provides a consistent represen-



tation of economic, demographic, technical, and policy factors



as they affect energy use and production and CO2 emissions.



     The global model is dissaggregated into nine regions (see



Figure B-2).  Its time horizon is long-term  from 1975 to



2100  with benchmark years 2000, 2025, 2050, and 2075.



Projections beyond 2050 have not been examined in detail for



reasonableness of parameters and model structure.  Eleven



types of primary energy in six major categories are currently




considered (see Table B-l).  In addition to the supply and demand




for energy by region and forecast period, the model also estimates

-------
                                 -67-
                              FIGUKE  B-2

              GEOPOLITICAL DIVISIONS IN THE  IEA MODEL
  K.y:

  1. USA
  2. OECO WEST (Carudl Hid WUm Europ*)
  3 JANZ (Japan. Auilrln >nd Ntw Zwlandl
  4 EUSSR (EnternEurop* wid USSR)
  6. ACENP (AiiHt Camrilly PUnned)
  6. MlDEST (Mldli El)
  7 AFR (Alricj)
  6 LA Ilitin Anwricl)
  9. SEASIA (South md Eul Ami
world  and  regional  energy prices  consistent  with overall  global

energy  balance.   The  structure,  data base,  output,  and  usage of

the model  are extensively documented.^/

Energy  Demand

     Energy demand  for each of  the six major fuel  categories is

developed  for each  of the nine  regions separately.   Five major

exogenous  inputs  determine energy demand:  population,  economic

activity,  technological  change,  energy prices, and  energy taxes

and tariffs.

-------
                             -68-
                    TABLE B-1

     PRIMARY FUEL TYPES IN THE IEA MODEL


OIL

     CONVENTIONAL

     UNCONVENTIONAL (ENHANCED RECOVERY, SHALE OIL,
     AND TAR SANDS)

     SYNTHETIC (FROM COAL AND BIOMASS)


GAS

     CONVENTIONAL

     UNCONVENTIONAL (DEEP WELLS, TIGHT FORMATIONS)

     SYNTHETIC (FROM COAL AND BIOMASS)


SOLIDS

     COAL

     BIOMASS

RESOURCE-CONSTRAINED RENEWABLES
    HYDROELECTRIC

NUCLEAR
SOLAR
     SOLAR ELECTRIC (OTHER SOLAR IS ASSOCIATED WITH
     CONSERVATION)

-------
                              - 69 -






     An estimate of GNP for each region is used as a proxy for



the overall level of economic activity and as an index of income.



While the level of GNP is an input to the system, it is derived




from assumptions on demographic growth and levels of labor




productivity.




     World population was assumed to stabilize by 2075, based on




work done by Keyfitz et al.^/  Labor productivity growth for




the high scenario was assumed to be 3.2 percent per year in 1980,



declining linearly to 2.2 percent per year by 2100.



     In the low scenario, labor productivity growth was assumed to




start at 2.2 percent per year in 1980 and to decline linearly to



1.7 percent per year by 2100.  Both the high and low estimates of



productivity growth utilize rates below the average rate of increase




around the world in the last thirty years.  The mid-range estimate



was an interpolation of the two curves.




     The energy technology parameter is a time-dependent index of




energy productivity, given constant energy prices and real incomes.



That is to say, it reflects improvements in energy efficiency



beyond those stimulated by increases in real prices or decreases



in real income.  In the past, technological progress has had an



important influence on energy use in the manufacturing sector of



advanced economies.  The inclusion of an energy technology para-




meter allows scenarios to be developed which incorporate either




continued improvements or technological stagnation as an integral



part of energy use scenarios.  A constant improvement of 25

-------
                              - 70 -






percent for each 25-year period was assumed for the industrial




sector in all OECD countries (no change was assumed for the




other sectors for these countries), and a 10 percent improvement



was assumed for the single aggregate sector in other countries.




     The final energy factor which influences demand is energy



price.  Each region has a unique set of energy prices which are




derived from world prices (determined in the energy balance




component of the model), transportation costs, and region-specific




taxes and tariffs.  The model can be modified to accommodate



non-trading regions for any fuel or set of fuels.  It is assumed



that no trade is carried on between regions in solar, nuclear,



or hydroelectric power, but that all regions trade other types of



fuels.




     The four secondary fuels (refined oil, refined gas, refined




coal, and electricity) are consumed to produce energy services.



In the three OECD regions (Regions 1, 2, and 3 in Figure B-2),



energy is consumed by three end-use sectors: residential/commer-



cial, industrial, and transportation.  In the remaining regions,



final energy is consumed by a single aggregate sector.



     The demand for energy services in each region's end-use




sector(s) is determined by the cost of providing these services,




and the levels of income and population.  The mix of secondary




fuels used to provide these services is determined by the relative



costs of providing the services using each alternative fuel.

-------
                              - 71 -


     The price of secondary fossil fuels is a function of the

regional price of primary fuels and the cost of refining:

                        Pjr = Pir(9ij) + hj

                        Pir = (Pi + TRir) TXir


Where:  Pjr is the price of secondary fuel j in region r;
        Pir is the price of primary fuel i in region r;
        gij is the efficiency of refining i into j ; hj is
        the nonenergy cost of refining; P^ is the world
        market price of fuel i; TRir is the cost of
        transporting fuel i to region r, and TXir are
        taxes on fuel i in region r.

     The demand for fuels to provide electric power is then

determined by the relative prices of the alternative electricity-

generating fuels.  Likewise, the demand for synthetic oil and

gas from coal and biomass are functions of oil and gas prices.

Finally, production levels of primary energy sources are derived

from the demand for secondary fuels.

Energy Supply

     Three generic energy supply categories are distinguished:

resource-constrained conventional energy, resource-constrained

renewable energy, and unconstrained energy resources.  There are

eight different supply modes across these categories, as shown

in Table B-2.  Production of conventional gas and oil are repre-

sented by a logistics curve which reflects historical supply

levels and estimates of remaining deposits:

                        F(t) = exp(a + bt)
                      l-F(t)
Where: F(t) is the cumulative fraction of the total resource
     exploited by time t, and a and b are empirical parameters.

-------
                                - 72 -



Production  rates of these  fuels are thus insensitive  to price

levels.




                            TABLE B-2

                 DISTRIBUTION OF IEA FUEL TYPES
                   ACROSS SUPPLY CATEGORIES


                        Supply Categories
     Resource-
     Constrained
     Conventional
     Energy
    Conventional Oil
    Conventional Gas
Resource-
Constrained
Renewable
Energy
Hydro, Bioniass
Unconstrained
Energy
Resources
Unconventional Oil
 (primarily oil shale)
Unconventional Gas
 (primarily gas)
Synthetic Gas
 (from solids)
Synthetic Oil
 (from solids)
Coal
Solar
Nuclear
     Production levels  of  unconventional oil and gas,  nuclear,

solar, and  solids (coal and biomass)  are modeled as  "backstop

technologies."  That  is, a base level of production  is assumed  to

be generated over time  if  real prices remain constant.  Shorter-

term supply schedules are  then superimposed on these long-term

trends to reflect the increase or decrease in production due to

-------
                              - 73 -


price rises or declines.  If the price falls below a breakthrough

price level, then production ceases.  These relationships are

encompassed in the following general expression:

                        P = a [exp(g/b)C]


Where:  P is the price of the backstop fuel; a is the break-
        through price; b is a parameter which determines the
        "normal" backstop price; c is a price-elasticity con-
        trol parameter; and g is the ratio of output in year t
        to the base level associated with the backstop price.


     Production levels of synthetic oil and gas are driven by the

cost of solids, the cost of producing the synthetic fuel, and

associated nonenergy costs.  The share of coal or biomass

allocated to the production of synfuels is specified by a logit

share equation, with the relative cost of synfuels versus other

sources of gas and oil and the price elasticity of production as

key terms.

     Resource-constrained renewable fuels are considered constant-

flow sources.  That is, the rates of energy production are limited

by the availability of the resource.

     For the high scenario the price of supplying each energy

source was the "best guess" of the experts familiar with the

respective sources.  For the low scenario the cost of nuclear

energy was halved starting in 1980.

Energy Balance

     The supply and demand modules each generate energy supply

and demand estimates based on exogenous input assumptions and

-------
                              - 74 -








energy prices.  If energy supply and demand match when summed




across all trading regions in each group for each fuel, then the



global energy system balances.  Such a result is unlikely at any



arbitrary set of initial energy prices.




     The energy balance component of the model is a set of




rules for choosing energy prices which, on successive attempts,




brings supply and demand nearer a systemwide balance.  Successive



energy price vectors are chosen until energy markets balance



within a prespecified bound.  Figure B-3 displays the interactions



necessary to achieve a global energy balance.




CO2 Release




     Given the solution from the energy balance component of the




model, the calculation of CC>2 emissions rates is conceptually




straightforward.  The problem merely requires the application of



appropriate carbon coefficients (carbon release per unit of energy)




at the points in the energy flow where carbon is released.  Carbon



release is associated with the consumption of oil, gas, and coal.



Large amounts of CO2 are released from the production of shale



oil from carbonate rock and from the production of synthetic



fuels from coal.  A zero-carbon-release coefficient is assigned




to biomass, nuclear, hydro, solar, and conservation.  Table B-3



shows the CC>2 emission coefficients used in the IEA model.

-------
                                - 75 -
                             FIGURE B-3

         SUMMARY OF INFORMATION FLOWS AND PROCEDURES IN THE IEA
             MODEL TO BALANCE ENERGY SUPPLIES AND DEMANDS
                                r
REGIONAL
POPULATIONS



REGIONAL
LABOR
FORCES

REGIONAL
LABOR




REGIONAL
GNP

TECHNO-
             PRODUC-
             TIVITIES
LOGICAL
CHANGE
                                   REGIONAL
                                   ENERGY
                                   DEMANDS
                                                   GLOBAL
                                                  SUPPLIES
                                                    AND
                                                  DEMANDS
                                   REGIONAL
                                    ENERGY
                                   SUPPLIES
Model Results
     Three  separate scenarios were examined in conjunction with
this study:
     1.   High economic growth with the more expensive  nuclear
          power production  costs produced  a 2.345% annual  growth
          in carbon emissions.

     2.   Slow economic growth with the more expensive  nuclear
          power production  costs produced  2.074% annual  growth
          in carbon emissions.

-------
                             - 76 -

                       TABLE B-3
     CO 2 COEFFICIENTS FOR CARBON-PRODUCING
                FUELS IN THE CO? MODEL
 FUEL                                    CARBON RELEASED
                                (TERAGRAMS OF CARBON PER EXAJOULE)
 LIQUIDS                                         19.7
 GASES                                          13.8
 COAL                                           23.9
 CARBONATE ROCK (SHALE) MINING AND PROCESSING       27.9
 COAL LIQUIFACTION                               18.9
 COAL GASIFICATION                                26.9
     3.   Slow economic  growth  with  halved  nuclear power production
         costs produced a  1.674%  annual  growth  in carbon emissions.
     The CC>2 emissions  used  for  the three  scenarios  are depicted
in Figure B-4.
Reasonableness of  the Assumptions
     The forces that determine emission  trends  -- long-term
population, labor  force, and productivity  growth, changes  in  energy
supply and demand, additions to  the resource  base, and  the  inter-
action of these factors in a supply-demand framework -- are
difficult to project.   For example, energy technologies could
change much more radically than  currently  foreseen.   Large-scale
biomass production might become  much more  feasible in the  next
century as an energy  source  if recombinant DNA  and other biotech-
nologies produce supercrops; large  fossil-fuel  reserves might be
discovered, which would radically decrease fossil-fuels costs;

-------
                                  17-
                                FIGURE B-4

                    GLOBAL CO2 EMISSIONS,  1975-2100
                         (Billions of Tons of Carbon)
m
cc
3
CO
O
LL
O
CO
O
en
     90
     80
     70
60
50
     40
     30
     20
     10
         1975
               2000
2025       2050

    YEAR
2075
2100

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                              - 78 -






new technologies might be developed that vastly reduce the costs



of extracting hydrocarbons from shale or tar sand;  or nuclear




fusion might become a commercial reality sooner than expected.




Any of these "surprises" would alter fuel use and emissions in




ways unanticipated by our analysis.  Although counting on such




surprises would be foolish for a study like this, our conclusions



must be tempered by the realization that the future may be very




different from the extensive range of possibilities currently




envisioned as possible.




     With respect to the scenarios generated, the assumption that



nuclear energy costs could be instantaneously halved in 1980 is



overly optimistic.  It was used simply to test the implications



of a radical shift in the cost of a major energy source that does



not emit CO2-  Other experiments with the model, such as doubling




or tripling the cost of fossil fuels, had negligible effects on




atmospheric temperatures.^/




     Although the IEA energy model was designed for long-range policy



analysis and satisfies this overriding objective, it does not con-



sider the capital constraints that may limit the rates of substi-



tution among competing fuels.  By ignoring potential bottlenecks



that could result, the model tends to overestimate the degree




to which rapid change in energy supplies is possible.  However,




since the results of this study (projections of sea level rise)



were relatively insensitive to energy projections, this limitation




of the IEA model is not critical.

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                              - 79 -






THE ORNL CARBON CYCLE MODEL



     The Oak Ridge National Laboratory carbon cycle model repre-



sents flows and stocks of carbon on a global scale._5/  Terrestrial



carbon is modeled in considerable detail, while ocean carbon is




represented by a simple box-diffusion model.  A general overview



of the model is presented here.




     Figure B-5 depicts the overall structure of the model.



Carbon in living material is divided between ground vegetation,



the wood parts of trees, and the non-wood parts of trees.  Dead



organic matter is divided between detritus/decomposer and active



soil carbon.  Finally, carbon in the oceans is subdivided into




surface (less than 260 meters below sea level) and deep layers.




     For each of the carbon reservoirs, equations specify maximum




stocks of carbon and rates of flow into and out of the reservoirs.



In general, terrestrial flows are modeled as linearly dependent



on carbon content of the i   donor reservoir (F^- = a C^) or as




a more complicated logistics function.  (Details of the structural



equations can be found in Emanuel, et al., 1981.)



     The logistic functions for trees include terms for carbon



release to the atmosphere from forest clearing.  Permanent forest



clearing is reflected by reductions in the parameters governing



storage capacity.  Where clearing is temporary, reestablishment



of forests occurs in a delayed exponential fashion.  (No future




clearing option was assumed in this study.)

-------
                              -  80  -
                            FIGURE B-5

          STRUCTURE OF THE ORNL CARBON CYCLE MODEL
                                              ORNL - DWG B1 6057 ESD
ATMOSPHERE
   GROUND
 VEGETATION
NONWOODY PARTS
   TREES
                        WOODY PARTS
                           TREES
                   DETRITUS/
                  DECOMPOSERS
                  ACTIVE SOIL
                   CARBON
SURFACE OCEAN
                             DEEP OCEAN
           MNM,cM      FROM AN UpDATED MANUSCRIPT BY W.R.
           EMANUEL AND OTHER AT OAK RIDGE NATIONAL LABORATORY.


     Net uptake  of  carbon by the oceans  is limited by  the  avail-

ability of carbonate  ions.  The rate at  which gaseous  CC>2  dissolves

in seawater  depends on the rate of  reaction with CO3,  which is

the first  step of a process by which CC>2 is incorporated into

various  seawater carbonate compounds.

      The  rate at which  carbon  flows among the  various  reservoirs

 is generally dependent  on  atmospheric temperatures.   Sensitivity

 to  temperature  is  significant,  because a  rise  in temperature  is

 likely to accompany  an  increase in  atmospheric CO2.   The original

-------
                              - 81 -






version of the ORNL represented this temperature-CC>2 relationship



by a simple exponential equation, rather than through a series of



heat-flux equations.  This portion of the model was replaced by



the relatively sophisticated heat-flux relationships in the



GISS model, by coupling the two models (see the discussion under




"Coupling the GISS and ORNL Models").



     The model inputs are estimates of fossil-fuel carbon emis-




sions on a yearly or longer time period basis from 1980 until




some future year.  (The IEA model estimates are on a 25-year



basis.  Estimates were provided on a 5-year basis by interpola-



tion of the 25-year estimate.)  Outputs are atmospheric CO2 for




5-year intervals.



     The model simulates historical patterns of carbon cycling




from 1740 to 1980 on an annual basis.  The resulting time trend




in CO2 was modified slightly so that the concentration in 1980



was 339 ppm.  This corresponds to the level estimated by the GISS



model in 1980, given estimates of fossil fuel carbon emissions in



1975 (the starting point of the IEA model) used in this study.



The model was then run to produce estimates of atmospheric C02



from 1980 to 2100.



Reasonableness of the Assumptions



     The fraction of carbon emissions retained in the atmosphere



is the product of a complex biogeochemical cycle that evolves




over time.  Evidence indicates that as the atmospheric concentration

-------
of CC>2 increases, the fraction retained in the atmosphere



will also increase.   Consequently, using a constant fraction




airborne is a very conservative assumption.



     The number chosen for the low estimate was 53%, the best




estimate of the historical fraction airborne.^/  A lower number




could have been chosen, based on the work of Woodwell et al.,



which states that past estimates of the biosphere's contribution




were too low arid thus caused fraction airborne estimates to be



too high.V



     Lugo and other biologists, along with Broecker and other



oceanographers, however,- have challenged the Woodwell estimates./




Broecker has shown that the oceans do not have the physical




capacity to absorb CC>2 contributions from the biosphere as quickly



as Woodwell had originally estimated, and Lugo has shown that




Woodwell underestimated tropical forest regrowth, thereby over-



estimating net forest contributions.




     Although it is a strong challenge to the Woodwell estimate,



the rebuttal is not absolutely conclusive.  Nevertheless, because



all carbon cycle models show fraction airborne increasing over



time, use of 53 percent probably constitutes a very conservative




estimate of retained CC>2 emissions.  The ORNL model modifies



the fraction airborne over time by taking into account water




heating and changes in ocean chemistry as well as temperature-




sensitive changes in carbon flows among all compartments.

-------
                              - 83 -






     Even the URNL carbon cycle model, however, is oversimpli-




fied, representing the oceans as a layered vertical column or box,




and the biosphere by only a few types of vegetation.  Ocean dynamics




are far more complex, containing complicated and interdependent




vertical and horizontal transports.  Ocean chemistry is not well




represented in models of the carbon cycle, and sources and sinks




may be over- or underestimated.




     The impacts of CO2 and temperature change on photosynthesis




and changes in ecosystems are not considered by these models.




The inaccuracies produced by such emissions have not been estimated.






INCREASES IN CONCENTRATIONS OF TRACE GASES
     Increases in the concentrations of trace gases will add




significantly to the warming from CO2-  This report considers




four of the most important gases: methane, nitrous oxide, CF2C12




(CFC-12), and CFC13 (CFC-11).




     Scientific knowledge of these gases is sufficient to separately




project emissions and atmospheric residence time only for chloro-




fluorocarbons.  We assume that the half-lives of CFC13 and CF2Cl2



will be 60 and 120 years, respectively.  The low, mid-range, and




high scenarios assume that emissions will increase annually by




0.7, 2.5, and 3.8 percent of the 1980 level until 2020.   Because




these emissions will also cause depletion of stratospheric ozone,




we assume that additional restrictions will be placed on their use




and that emissions will remain constant after 2020.  Because of




the long residence times for these gases, their concentrations

-------
                              - 84 -


will continue to increase throughout the twentyfirst century in

all scenarios.    Table B-5 shows the resulting concentrations

of these gases in 25-year intervals.
                            TABLE B-5

              CONCENTRATIONS OF CHLOROFLUOROCARBONS
                       (parts per billion)
                               Year
                    1980
2000
2020
2040
2060
2080
2100
Low Scenario
CFC13 (CFC-11)
CF2Cl2 (CFC-12)
Mid-Range Scenario
CFC13
CF2C12
High Scenario
CFC13
CF2C12
.18
.31

.18
.31

.18
.31
.37
.69

.41
.76

.44
.84
.54
1.06

.69
1.34

.79
1.64
.68
1.44

.95
1.94

1.14
2.51
.79
1.73

1.15
2.46

1.40
3.27
.88
2.00

1.30
2.91

1.60
3.93
.94
2.25

1.42
3.32

1.76
4.51
     Existing knowledge of the environmental fates of methane

and nitrous oxide did not permit us to model the biogeochemical

cycles for these gases.  Instead, we projected their concentrations

directly.  For the low scenario, we assumed that the historical

trends in the concentrations of methane and nitrous oxide would

continue; for the mid-range and high scenarios, we assumed that

they would accelerate.  The concentration of nitrous oxide was

assumed to increase from the 1980 level (0.3 ppm) geometrically

by 0.2, 0.45, and 0.7 percent per year for the three scenarios

-------
                               -85-
(Weiss, 1981).  The concentration of methane was assumed to

increase annually by 1.0, 1.5, and 2.0 percent for the three

scenarios from the 1980 level of 1.6 ppm (Rasmussen, 1981).


SEA LEVEL RISE MODEL AND THE GISS ATMOSPHERIC TEMPERATURE

     The GISS model used in this study was based on a one-dimen-

sional radiative-convective (RC) model for estimating temperature

increases associated with atmospheric CC^ rises.^/  A routine for

estimating sea level rises in response to temperature fluxes

generated by atmospheric forcings was added for this study.

     The RC model computes vertical temperature profiles over

time from net radiative and convective energy fluxes.  Radiative

fluxes, in turn, depend on changes in atmospheric gases, especially

CC>2, and on the associated feedback effects.  The GISS equation

used here is based on an empirical fit to the RC model.

     The fitted equation, described in Hanser. et al., was modified

by Lacis for this study to incorporate trace greenhouse gases.

Heat Flux Computations

     The heat flux into the earth's surface is estimated by an

equation that contains all key temperature-related terms:

F(t) = 2.6xlO~5( A C02)       - 5.88xlQ-3(  A T) + 3.685xlO"4 ( A T)2
       [1 +.0022( n C02)]'6      T0              "TT2
                                   t^                ^

     - 4.172xlO~7 ( A C02) ( A T) + 1.197x10-3 ( A CH4)-5
        Te

     + 5.88x10-3 ( A N20)-6 + S.lSxlO"4 (  A CCS) + 3.78xlO~4 ( A CC2)

     - 1.197xlO-4 ( A CH4)( N20) - 2.40x10-2 ( A V) - 2.10xlO~3 ( A V)2
     - 1.17x10-3 ( A T)( A V) + 3.184X10-1 ( A S)

-------
                              - 86 -
Where:  F(t) is the heat flux as a function of time in cal min 1 cm 2

           A C02 is the change in atmospheric CC>2 from the 1880
              value (293 ppm) in ppm.
           A T is the change in atmospheric temperature (surface
              level) from the 1880 value in C
           A CH4 is the change in atmospheric CH4 from the 1880
              value (1.6 ppm) in ppm.
           A N20 is the change in atmospheric N20 from the 1880
              value ( .300 ppm) in ppm.
           A CC3 is the change in CC^F from the 1880 value
              (0 ppb) in ppb.
           A CC2 is the change in CC12F2 from the 1880 value
              (0 ppb) in ppb.
           ^ V is the change in atmospheric optical depth from
              a baseline level due to volcanic activity in dimen-
              sionless units.
           A S is the change in solar luminosity from a baseline
              level in fractional units.
           A Te is the temperature equilibrium sensitivity -- the
              assumed temperature rise when CC>2 doubles from the
              1880 level (from 293 to 586 ppm).

     The heat flux is estimated for time periods ranging from

each month to each year (a semimonthly time step was used in this

study).  The appropriate  A T value for calculating F(t) in each

time period (t=n) is the value estimated for the previous period

(t=n-l).  For a simple one-layer ocean model,  A T is obtained by

solving the following differential equation:

                           d A T = F(t)
                            dt      C0

Where:  Co is the heat capacity of the mixed layer of the

ocean per unit area (cal cm~2).

     Estimates of heat flux from the empirical equation described

above were compared by Lacis with the RC model calculations.  The

two estimates agreed to within one percent for CC>2 values of 0 to

1220 ppm, and to within 5 percent for CC>2 values of 1220 to

-------
                              - 87 -


1700 ppm.^y   Values for the parameters in the empirical

heat-flux equation were obtained as follows:

      A  CC>2:  value obtained from the IEA and ORNL models;
      A  CH4-.  1.6 ppm from 1880 to 1980; concentrations after 1980
              increase as described in section on trace gases.
      A  N20:  0.300 ppm in from 1880 to 1980; concentrations after
              1980 increase as described in section on trace gases,
      A  CC2 and  A CCS:  See Table B-5.

      A V: constant 0.007 or 0.037 each year for 1980 to 2100

      A S: 0 for 1880 to 2100; or 0 for 1880 to 1980 and increased

           or decreased by 0.005% per year for 1980 to 2100.

      Te: 1.5C, 3.0*C, and 4.5*C.


Changes in Volcano Aerosols and Solar Irradiation

     For special cases changes in aerosols and solar luminosity

were considered.  Aerosols and dust that are produced by volcanoes

can lower global temperatures by increasing reflection of incoming

energy.  A higher estimate of optical depth than the baseline was

used as a special case.

     Baseline optical depth = .007 each year (dimensionless units)
     High optical depth = .037  each year (dimensionless units)

     An optical depth of 0.037  is the highest twenty-year

average in the last century, while 0.007 is the average over

the period 1900-1980.  No basis exists for assigning a different

value across a whole century.  To sustain the high value over

the next 120 years would require a continuation of levels of

volcanic activity that have been sustained for decades, at most,

in recorded history.

     Recent evidence indicates some possible shifts in solar

luminosity making the term "solar constant" a bit of a misnomer.

-------
                               -88-


Two special case scenarios were considered:

        Special Cases: 0.5% increase over 100 years and

                       0.5% decrease over 100 years

     A one-half percent decrease in solar luminosity is much

greater than would be likely in the time period under considera-

tion.  However, even such an improbably large variation would not

overwhelm the greenhouse effect.


Diffusion of Heat in the Ocean

     The ocean model consists of a mixed layer of depth Hm = 100m

and a thermocline with 62 layers and depth H = 900m.  The mixed

layer temperature is assumed to be independent of depth, while

the thermocline temperatures are defined by a diffusion equa-

tion with constant thermal diffusivity.   The layering is different

from that used in the ORNL model, but the difference is not of

importance in generating the expansion.

     The temperature change in the mixed layer ( A Tm) is a solu-

tion of the equation:

                cHm  d A Tm   = F(t) - FD(t)
                      dt

where c is the heat capacity of water, Hm is the depth of the

mixed layer, F(t) is the heat flux from the atmosphere into the

ocean and

                FD(t) =  - x aA T
                              3 z z=Hm


is the heat flux from the thermocline into the mixed layer.

-------
                              - 89 -


Note that our z-axis is directed toward the bottom of the ocean.

Also, we use g, cm, sec and cal, so the heat conductivity lamda

is n.umercially equal to the heat diffusivity K.  Values for

diffusivity were set at either 1.18 or 1.9 cm2/sec.  (Special

scenarios investigated values of 0.2 and 4.0 cm^/sec.)

     The temperature change in the thermoclir.e ( ^ T) is determined

by the diffusion equation:

               c SA T(z,t)  = k  a2A T(z,t)
                    3 t             6 z2

     The boundary conditions for  A T are:

                       A T =  A Tm  at z = Hm

and zero heat flux at the bottom of the thermocline:

           ISA T   = 0 at z = H + Hm.
              3 z
Thus it is assumed that no energy escapes through the lower

boundary of the thermocline.  Note that  A Tm and  A T are

temperature changes of the mixed layer and the thermocline

between the initial time (1880) and time t.  It is assumed that

in the year 1880  A Tm =  A T =  and thus that the ocean

temperature was in a state of equilibrium with the atmosphere at

that time.

     Required input data are atmospheric CC>2 levels on a yearly

or longer time period.  Five-year estimates were obtained from

the ORNL, or alternatively, by multiplying a fixed-retention

factor times the interpolated five-year estimates of carbon

-------
                              - 90 -


emissions from the IEA model.  GISS outputs are estimates of

ocean temperature increases on a five year basis.

     The use of diffusivity coefficients as a surrogate for all

circulation processes that transport heat may fail to describe

the time paths well, with the downward heat transport in the

latter period probably being overestimated because of increasing

oceanic stability.  Nevertheless this method simplified the

problem substantially and a range of different possible coeffi-

cients was used to investigate the sensitivity of the overall

estimate to the rate of downward heat transport.

These coefficients are:

               High:   = 1.9 cm2/sec
                Low:   = 1.18 cm2/sec
  Special Scenarios:   = 0.2 cm2/sec  (minimum)
                       = 4.0 cm^/sec  (maximum)

     The range of coefficients used, 1.18 to 1.9 cm^/sec

is representative of mean oceanwide mixing rates as determined

by the NSF-sponsored transient tracer experiment and others.

Variation in estimates of the exact value of the data depend

on the tracer used and the statistical method of computing

the global mean.   We tested 0.2 and 4.0 cm2/sec to account

for the possibility of dramatic changes in ocean transports due

to deglaciation and climate change.

-------
                              - 91 -



Sea Level Rise

     Given a time trend in ocean temperature rise, the sea

level change is estimated as:

                              Hm+H
                        A H = r dz A a
                              o     a

where a is the specific volume and  ^ a is its change due to

thermal expansion.  For this computation an ocean temperature of

10C and salinity of 35 per mille are used.  In other words, the

mixed layer and each of the 62 layers in the thermocline expand to

a degree that reflects the average pressure, and the rise in

temperature of the layer (as reflected by the change in density).

The average global rise in sea level is the output from this

component of the model.


Crustal Movements

     Systematic changes in the topography of earth's land or

oceans can alter apparent sea level.  No changes were assumed

however, because global variations occur over a vastly longer

time scale than the 120 year period considered here.  Clark et al.

estimated that long-term isostatic adjustment of the earth's

surface has caused a worldwide sea level change of 1 meter per

5000 years (2 centimeters per century).^/  In certain regions,

coastal movements can substantially increase or decrease local

sea level rise.  However, such trends are likely to balance out

worldwide.

-------
                              - 92 -








COUPLING THE QRNL AND GISS MODELS




     The general .methodology for estimating thermal expansion of



the oceans was outlined in Figure B-l.   Of the two pathways for




translating carbon emissions from fossil fuel combustion into




atmospheric CO2 concentrations (assuming a retention factor and



running the ORNL model), this section focuses on the use of the




ORNL model.  As discussed previously, using the ORNL model to




estimate atmospheric concentrations of  C02 requires the coupling



of the ORNL and GISS models and an iterative procedure using the



GISS model alone.  The discussion in this section emphasizes the




sequence of actions employed to couple  the two models, and the



procedures for iterating within the GISS model.




Calculating Initial Temperature vs. Time Curves




     The starting point for the analyses that use the ORNL



model is the estimation of a family of  temperature-time curves




using the GISS model.  These curves are employed in the ORNL



model to describe a range of future increases in sea surface



temperature (in response to rising atmospheric CO2) which, in



turn, will affect the rate of CO2 exchange among sources and




sinks.  Essentially, the time trends of temperature, generated



by a fairly sophisticated treatment of  heat flux in the GISS



model, replace the very simple CO2~temperature relationships in




the ORNL model.  The treatment of heat flux in the GISS model is



still a highly simplified representation of real ocean transports,

-------
                              - 93 -






as discussed above.



     To generate the GISS temperature-time curves, it is first




necessary to estimate an atmospheric CC^-time curve, since this is



the main driving function for the GISS model.  The most straight-




forward approach is to apply a constant retention factor to the




time trend of CC>2 emissions generated by the IEA model.   In other



words, the first step in this approach appears identical to the




other methodological approach.  in fact, a modification was



employed for these analyses:  changing retention factors (from



about 0.6 in 1980 to about 0.8 in 2100) were used to generate




the preliminary atmospheric C02~time curves.




     The GISS model was then run with high and low temperature/



C02 sensitivity (Te) values, with and without trace gases, to




produce a family of curves of sea-surface temperature versus time.




(Values for solar luminosity, volcanic activity,  and heat diffu-



sivity were specified in each scenario.)  These curves are repre-




sented by a quadratic equation of temperature versus time with




parameters a and b.  The parameter a is the temperature difference



between 2100 and 1980; b is the temperature difference between




2040 and 1980 divided by a.  These parameters are then used to



calculate coefficients for the quadratic equation T = ct + dt2 + 293,



where T is the temperature rise after 1980 (K),  and t is the number



of years after 1980.

-------
                              - 94 -
     Four new curves reflecting the extreme values observed for a




and b were then specified:



                               a
            Highest
            Lowest
                      Highest
Case 1
Case 3
           Lowest
Case 2
Case 4
These curves bound all possible changes in temperature, given the




time trend in atmospheric CC>2 specified previously.  The four



combinations of values for a and b are then transmitted to the




ORNL model.




Calculating CO2 v. Time Curves with the QRNL Model



     The ORNL model is next employed to estimate future increases




in atmospheric CC-2, using the fossil-fuel CC>2 emission scenarios




from the IEA model and the four sea-surface-temperature time



trends from the GISS model.  Since four separate temperature/




time curves are employed, four separate CC^-time curves are



generated as output.  Each CC>2 curve is represented by estimates



of atmospheric CC>2 concentrations in 10-year intervals from 1980



to 2100.  Thus, a 4 by 13 matrix of values (corresponding to the



four time v. temperature curves and the thirteen inclusive




decades between 1980 and 2100) is generated as output.






Estimating Final Temperature v. Time Curves




     The four "refined" time projections of CC>2 are returned to



the GISS model to obtain a consensus temperature versus time

-------
                              - 95 -






curve.  This is accomplished by selecting one of the CC>2 curves



as a starting point.  (Tests have demonstrated that starting from




any one of the four curves will yield tne same result.)  The GISS



model is then run to obtain a corresponding temperature curve



from 1980 to 2100.  This temperature curve is compared with the




four temperature curves originally generated by the GISS model



and transmsitted to the ORNL model.  The new temperature curve is




composed by interpolating among the four previous curves, and




a new C02 curve is estimated corresponding to the interpolated



temperature curve.  (In essence, this is a two-way interpolation



for each 10-year interval.)  The whole process is repeated until




two successive temperature curves closely approximate each other.



Usually, this takes no more than two iterations.




     To check the "accuracy" of such an iterative approach, the




final temperature-time curve from GISS was used as input to the



ORNL model for a small sample of runs.  The resulting CO2~time



curve from ORNL was compared with the final C02~time curve in GISS.




In all cases, the two agreed within 2 ppm for each 10-year interval



Estimating the Contribution of Thermal Expansion to Sea Level Rise



     Once the final projections of expansion to sea level rise are




obtained, the equations in GISS relating ocean volume, temperature,



and pressure described previously are employed to estimate thermal



expansion.  The increase in ocean volume is then translated into




global mean sea level rise.

-------
                         - 96 -
                END NOTES TO APPENDIX B
The rationale for coupling the GISS and ORNL models in this
fashion is based on (a) the sensitivity of many C02 uptake
and release equations to temperature in the ORNL model, and
(b) the more sophisticated treatment of heat flows and
temperature changes in response to C02 increases in the GISS
model.  An alternative approach would be to replace the simple
temperature equations in the ORNL model with the GISS equa-
tions, in essence combining the two models.  However, the
ORNL model is much more expensive to run than the GISS model.
Thus, the coupled approach employed here is a cost-effective
way to upgrade the treatment of temperature in the carbon
cycle model.

To illustrate the difference in results between the two basic
analytical approaches (fixed-retention factor with the GISS
model v. coupled ORNL-GISS modeling), we have listed
estimated atmospheric CO2 levels and sea level rise from
1980 to 2100 in the following table for each approach.
Two sets of results are listed for the coupled ORNL-GISS
modeling results  the initial outputs from the ORNL and
the final outputs from the GISS model.  As shown, the
coupled ORNL-GISS approach produces higher estimates than
the fixed-retention-factor approach.  This is reflected
in the retention factor inferred from the ORNL-GISS modeling,
which varies from 0.53 in 1980 to 0.72 in 2100.

A second observation concerns differences between the two
sets of ORNL-GISS outputs.  The initial ORNL CO2 (or sea
level rise) time curve is higher than the final iteration
from GISS, reflecting the fact that the ORNL results repre-
sent one of the four extreme temperature-versus-time curves.
The final iteration from GISS is a C02 time curve interpolated
among the extremes, as discussed in the section on coupling
the ORNL and GISS models.

-------
                               - 97 -
        ESTIMATED ATMOSPHERIC C02 LEVELS AND SEA LEVEL RISE
             USING THE TWO BASIC ANALYTICAL APPROACHES

        (High-Growth Scenario, High-Temperature Sensitivity,
                          No Trace Gases)
      Fixed-Retention Factor
Coupled ORNL-GISS Modeling

(0.
53A)*
Ini
tial
ORNL Results

1980
1990
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100

CO2 Level
(ppm)
339
354
370
392
420
457
511
584
676
787
919
1083
1281

Sea Level
Rise (cm)
0
0.99
2.22
3.72
5.58
7.88
10.80
14.52
19.13
24.68
31.19
38.71
47.31

CO 2
Level
(ppm)
339
359
382
412
451
502
578
681
814
979
1181
1439
1756
Sea
Level
Rise
(cm)
0
1.06
2.47
4.27
6.57
9.45
13.15
17.86
23.71
30.77
39.04
48.63
59.59
Final
Iteration

CO2
Level
(ppm)
339
356
375
401
436
482
555
654
784
947
1147
1403
1720
GISS
Results
Sea
Level
Rise
(cm)
0
1.02
2.32
3.95
6.03
8.66
12.09
16.56
22.19
29.05
37.16
46.62
57.48
* A is a conversion factor to convert tons of carbon retained in
  the atmosphere into ppm of CO2.   A = 0.472 Gigatons of Carbon
  per ppm of CO2.

-------
                              - 98 -
 2/   Edmonds, Jae and John Reilly, 1982b.  Global Energy and CQ2
         to the Year 2Q50.   Oak Ridye, TN:  Institute for Energy
         Analysis, Oak Ridge Associated Universities.

      Edmonds, Jae, John Reilly, and Rayola Dougher, 1981.
         Determinants of Global Energy Demand to the Year 2050.
         Oak Ridge, TN:  Institute for Energy Analysis, Oak Ridge
         Associated Universities.

 3/   Keyfitz, Nathan, et al. 1983.  Global Population (1975-2075)
         and Labor Force (1975-2050).  Oak Ridge, TN : Oak Ridge
         institute for Energy Analysis, Oak Ridge Associated
         Universities.

 4/   Seidel, Stephen and Dale Keyes, 1983.  Can We Delay A
         Greenhouse Warming?. Washington, DC:  U.S. Environmental
         Protection Agency.

 jj/   Emanuel, William R. ,  G.G. Killough, and J.S. Olson, 1981.
         "Modeling the circulation of carbon in the world's
         terrestrial ecosystems," in Modeling the Global Carbon
         CycleScope 16, Bert Bolin, et al., eds., New York: John
         Wiley.

 6/   Rust, Bert W., Ralph Rotty, and Gregg Marland, 1979.
        "Inferences drawn from atmospheric CO2 data."  Journal
        of Geophysical Research.  84:C6:3115-22.

 !_/   Woe-dwell, G.M. 1978.   "The carbon dioxide question."
         Scientific American.  238:34-43.

 __/   Lugo, Ariel, 1980.  "Are tropical forest ecosystems a new
         sink?" in The Role of Tropical Forests in the World
         Carbon Cycle, Sandra Brown, Ariel Lugo,  and Beth Liegel,
         editors.  Washington, D.C.: U.S. Department of Energy
         #CONF 800350. 1-18.

      Broecker, W.S., Tsung-Hung Peng, and R. Engh,  1980.  "Modeling
         the carbon system." Radiocarbon.  22:3:565-98.

9_/    Hansen, James E.,  et al. 1981.  "Climate impact of increasing
         atmospheric carbon dioxide."  Science. 213:4511:957-66.

10/   Lacis, A., personal communication.  Lacis,  A., et al. 1981.
         "Greenhouse effect of trace gases, 1970-1980." Geophyscial
         Research Letters.  81:10:1035-8.

-------
ll/   Sofia,  S.,  and A.S.  Endal,  1982.   "Solar variability."
         Reviews  of Space  Physics.

12/   Clark,  J.A.,  W.E.  Farrell,  and W.R.  Peltier,  1978.   "Global
        changes in  postglacial sea  level:   a numerical calculation."
        Quarternary Research.   9:265-87.

-------
                             - 101 -


                            APPENDIX C

         METHODS OF ESTIMATING SNOW AND ICE CONTRIBUTION
     This appendix reviews the results and methods used to gene-
rate the estimates of ice melting in the doubled C02 experiments
with the GISS general circulation model (GCM) and presents the
methods used to estimate snow and ice contributions in the
scenarios.

              GLACIAL MASS BALANCE IN GISS GCM
                       by Gary Russell
              Goddard Institute for Space Studies

     The GCM doubled C02 experiments imply a sea level rise of

13.5 mm/yr due to melting of land ice.  The melting is caused

by a mean addition of heat of 3.27 Wm~2 to the surface of the

land ice.  The increment of sea level caused by reduced snow on

the continents is insignificant compared to the glacial metling.

     The following is a short description of algorithms applied

to land ice in the GCM, tables of results from the control run

and the doubled C02 experiment, and calculations based on those

tables.

     Precipitation that falls on the ground is calculated from

the atmospheric conditions. Precipitation is snow if the first

atmospheric layer temperature is below 0C; otherwise it is rain,

        EPRCP (W/m2) =  0 if T1 > Q.
                                           [LHM = 334000 (J/kg)]
                       -PRCP*LHM if T1 < 0

        PRCP is the precipitation in kg/m^S

-------
                             - 102 -






The energy heat flux falling on the ground depends only on the




phase of the precipitation,  not additionally on the temperature



of the rain or snow; this is an inaccuracy, but the error is a




relatively small portion of  the total flux.  Rain over ice



immediately runs into the ocean.  SNOW (kg/m2) accumulates on the



surface.  Over land ice, when the snow exceeds 100 (kg/m2), some




of it is compacted into ice  so that the snow depth is reset to 90




(kg/m2).  The compacted ice  is accumulated (with a minus sign) in




the diagnostic MANDC.



     Evaporation is calculated in the surface interaction routine



and depends on the surface drag, surface wind magnitude, surface



specific humidity, and the ground temperature.




     EEVAP (W/m2) = EVAP * LH



          LH = 2500000 (J/kg) over water




          LH = 2834000 (J/kg) over ice




     EVAP is the evaporation in kg/m2s



The temperature at which evaporation occurs is ignored.



     Runoff over ice is the summation of rain plus melting of




snow or ice at the surface,  represented by RUNOFF 9kg/m2s).



Runoff carries no energy with it.  Over earth, runoff depends on



whether the ground is saturated and the energy of runoff is




     ERUN (W/m2) = RUNOFF *  T (C) * SHW    [SHW = 4185 (J/kgc)]

-------
                           - 103 -


     Other Energy Fluxes  depend on the ground temperature, the

atmospheric situation, the solar zenith angle, and surface albedo.

          ESENS (W/m2)  sensible heating

          ESOLR (W/m2)  net solar heating into the ice

          ETHRM (W/m2)  net thermal heat out of the ice

     Net Energy Fluxes into the ground (or ice) are calculated as

        ENET (W/m2) = EPRCP + ESOLR - ETHRM - ESENS - EVAP - ERUN

If ENET is negative, the temperature of the ground snow or ice is

reduced.  If ENET is positive, snow and ice are warmed until they

reach 0C.  At that point, snow is melted; after all the snow is

melted, the remaining energy melts ice.  The melted ice is

accumulated in the diagnostic MANDC.

     Melting and Compacting of glacial ice is a diagnostic of the

GCM called MANDC (kg/m2s), which is positive for melting.  The

following equality holds:

     d   (SNOW + WATER + ICE) = PRCP - EVAP - RUNOFF + MANDC.
     dt


SNOW, WATER, and ICE pertain to the first 4 meters in the ground.

MANDC comes from the ice below the first 4 meters.  Averaged over

an annual cycle in a run which has achieved equilibrium, c3  (SNOW
                                                         dt
+ WATER + ICE) should be nearly zero.  There is energy associated

with MANDC.

  EMANDC (W/m2) = MANDC * [T(C) * SHI - LHM], [SHI = 2060 (J/kgC)]

and an equation (for ice).

-------
                           - 104 -


        d
        dt [(SNOW + ICE)  * T * SHI] = ENET + EMANDC.

The time derivative was not calculated but is several orders

of magnitude smaller than ENET or EMANDC.


Sources of Error

    The results of the model should be interpreted in light of

the following sources of error:

1.  The major source of error is that the  climate model uses

    fractional grid, i.e., each grid box can can contain ocean,

    sea ice, land ice, and earth.  The composite surface

    albedo is an area-weighted average of  the albedos of the

    separate surface types, but once the composite surface

    solar absorption is calculated, it is  distributed into

    the surface types uniformly.  When ocean ice is replaced

    by open ocean, the composite albedo will decrease and the

    increased solar absorption should primarily go into the ocean.

    However, the model erroneously sends part of the absorbed solar

    energy into the land ice and ocean ice.  Correction of this

    feature of the model could significantly decrease the estimated

    melting rate of glaciers.

2.  Another aspect of the fractional grid is that sensible heating

    is proportional to the ground temperature minus the surface

    air temperature, but the air temperature is a composite of the

    entire grid box.  Because land ice is  at a higher altitude than

    sea ice and the ocean, the sensible heating over land ice is

    underestimated in both runs.  Because the net melting is the

-------
                            -105-
    difference between these two runs, the sign of the resulting




    error is not known.



3.  Areas of land ice in the model include Antarctica, Greenland,



    islands along the Arctic Ocean, and glaciers in southern



    Alaska.  Had alpine glaciers been included as well, the



    sea level rise from melting would have been somewhat greater.






General Comments on the Tables




1.  The hemispheric and global numbers for water and ice were



    produced with a resolution of hundredths of a mm/day or



    3.65 mm/yr.  The latitudinal numbers used a resolution




    of tenths of mm/day or 36.5 mm/yr.




2.  The hemispheric and global numbers for energy used a



    resolution of tenths of W/.m2 except for EMANDC which is




    know to a hundredth of W.m2.  The latitudinal numbers



    used W/m2.



3.  ENET is calculated by subtracting large numbers and is




    therefore less accurate.  EMANDC is a diagnostic accumulated



    directly in the GCM and should be much more accurate.



    (The latter is also true for MANDC).




4.  The numbers are based on a 10 year average (years 26-35)



    of the control run 882 and doubled CC>2 experiment 886.



5.  All numbers are per net area [1 (mm/yr) = 1 (kg/m2yr)].




    The associated area is all land area.




6.  .0106 (W) added to a square meter of ice will melt 1 (mm)



    of ice during a year.

-------
                           - 106  -


7.   The 33 (mm/yr)  of melting in  the difference 886-882

    applies to all  land.   The average melting over land ice is

    300 (mm/yr)  = 36 .291 (land area)
                     .032 (land ice area).

    Similarly, the  energy of melting in the difference 886-

    882 which applies to  all land is .36 (W/m2).   Applying

    this to the land ice  only it  is 3.27 (W/m2) = .36 .291
                                                      .032.

8.   The 3 (mm/yr) of melting of land ice in the control run

    882 would cause a sea level rise of

    1.23 (mm/yr) =  3 .291 (land area)
                     .709 (water  area)

    The 33 (mm/yr)  of melting in  the difference 886-882 would

    cause a sea level rise of

    13.54 (mm/yr) = 33 .291
                       .709

9.   The sea level rise implied by the reduction of snow on

    the continents  in 886, compared to 882, is

    1.59 (mm) = 3.75 .291
                     .709

    This contribution is  negligible, because it is a one-time

    change rather than a  rate as  in the above cases.

-------
Glob
NH
             - 107 -






            TABLE C-l






    Water and Ice                         Units: (mm/yr)




  Control run:  882                  Quantities refer to Land




SH    82N   74N  67N   59N   -67S  -74S  -82S   -90S
PRCP
EVAP
RUNOFF
d SNOW
dt
d( WATER + ICE)
dt
RUN+EV-PR
MANDC
Land
Percentage
Land Ice
Percentage
SNOW (mm)
960 931 1022
719 686 788
245 270 190
.05 .06 .02
-.4 -.6 0
3 25 -44
3 26 -44
29.1 39.4 18.8
3.2 4.3 2.1
17.6 15.7 21.6
329
73
292
1.1
0
36
37
15.0
13.2
95
438
110
402
.2
0
74
73
30.6
10.7
114
621
256
475
-.9
-.6
110
146
71.5
4.6
61
694
402
402
.2
-1.8
110
110
57.9
1.0
30
730
219
840
.2
0
329
329
15.4
15.4
55
475
73
73
-.2
0
-329
-329
66.0
66.0
82
183
37
0
.3
0
-146
-146
100.0
100.0
85
110
37
0
-.4
0
-73
-73
100.0
100.0
86

-------
                       - 108 -






                      TABLE C-2






                   Water and Ice




                Difference:  886 - 882
                                     Units:  (imi/yr)



                                     Land
Glob     NH
SH
82N  74N  67N   59N   -67S  -74S  -82S   -90S
PRCP
EVAP
RUNOFF
d SNOW
dt
d( WATER + ICE)
dt
RUN+EV-PR
MANDC
SNOW (mm)
157 131
110 95
80 55

212 73 110
146 0 0
128 475 255

182
110
182

Numbers are
33 19
33 21
-3.75 -4.8
62 402 145
62 365 146
-1.6 -21 2
110
73
-15
146
110
110

nearly
74
36
-15
146
-37
1314

0.
1131
1095
-11
146 110 73
0 37 0
219 73 0


73 0 -73
73 0 -37
-5 -4 1

-------
                         - 109 -
                     TABLE C-3
   Energy




  Control Run: 882
                                           Units:  (W/m2)



                                     Quanitities Refer to Land
Glob
NH
SH   82N   74N  67N   59N  -67S  -74S   -82S  -90S
ESOLR
ETHRM
ESENS
EEVAP
EPRCP
ERLJN
ENET
EMANDC
154.5
+48.0
47.5
57.3
-1.3
.4
-.07
-.01
150.2
+48.0
45.6
54.7
-1.4
.4
.17
-.29
163.3
+48.1
51.6
62.6
-1.2
.4
-.56
+.57
32
+23
1
5
-5
0
-2
0
42
23
6
8
-5
0
-1
-1
70
30
14
21
-3
0.1
1
 1
96
37
23
32
-3
0.1
1
-1
57
27
3
16
-7
0
3
-3
38
30
2
5
-5
0
-4
+4
38
33
1
4
-2
0
-2
+2
42
39
-1
4
-1
0
-1
+1

-------
                         - 110 -
                    TABLE C-4
     Energy



 Difference:  886 - 882
                               Units: (W/m2;



                                 Land
Glob     NH
SH   82N   74N  67N  59N   -67S  -74S  -82S  -90S
ESOLR
ETHRM
ESENS
EEVAP
ERPCP
ERLJN
ENET
EMANDC
0.7
-4.0
-4.2
8.6
0.1
0.1
.37
-.36
.6
-3.6
-3.3
7.4
.3
.1
.24
-.22
1.2
-5.0
-6.3
11.4
-.2
.2
.63
-.64
3
-2
0
0
-1
0
4
-4
2
-2
0
2
-1
0
2
-1
_1
-4
-5
7
0
0.1
1
-1
-1
-4
-5
8
1
0.1
0
-1
3
-4
-1
-3
1
0
12
-12
-1
-3
0
0
-1
0
1
-1
-2
-2
0
0
-1
0
0
0
__"J
-3
0
0
-1
0
-1
+1

-------
                            - Ill -






                INTERPRETATION OF GISS RESULTS



                       by John S. Hoffman



     The problems with interpreting the GISS model results




are twofold:



     1.  The model looks at the effects of doubled CO2 / while



         a projection would require looking at the system in




         transition from current CO2 levels, to the doubled



         level and beyond.  For the mid-range scenario,




         temperatures reach 4.1C in the GISS doubled equilibrium



         run by 2050.  A method needs to be developed to



         determine melting before this doubling and after it.




     2.  Melting in situ may not all run off.  Some percentage



         will refreeze, raising the temperature of the ice and



         changing its physical characteristics.  It is undetermined




         at this time whether those changes cause ice discharges




         greater than or less than if the melting had resulted



         in runoff.




     These problems are now being analyzed by a team from GISS,



NASA,  and Lamont-Doherty Geological Observatory, along with



several other issues.  In the preceeding analysis the results




were used only to check the general validity of the numbers



developed through our procedure of extrapolating historical



ratios, rather than to generate an ice and snow land-to-sea




transfer scenario.

-------
                            - 112 -


    THE USE OF THE HISTORICAL METHOD FOR GENERATING SNOW-ICE
                         CONTRIBUTIONS

                       by John S. Hoffman

     A variety of authors have estimated sea level rise in the

last century on the basis of tidal gauge stations.  The esti-

mates vary between 10 cm and 15 cm.  Using historical changes in

temperature, Hansen et al. and Gornitz et al. have varied CO2

increases and the heat absorption capacity of the ocean as

represented by the diffusitivity coefficent "K"._   For a Te

of 3C, and a K of 1.2 cm2sec~l, almost half of the total sea

level rise could be accounted for.  Sea level rose approximately

5 cm due to thermal expansion; thus, a 10 cm total rise implies

5 cm due to ice and snow transfer from land to sea, assuming

changes in other water reservoirs to be negligible.  However,

if the historical sea level rise was actually 15 cm, then

10 cm was due to ice and snow contributions, giving the higher

two-to-one historical ratio.  Barnett, the source of the 15 cm

estimate, attributes two-thirds of the rise to this source.^/

The scenarios of future sea level are simply extrapolated past

ratios, one to one as the low, two-to-one as the high.  This

ratio generates estimates within the contribution capacity of

the ice sheets, alpine glaciers, and other water sources on

land based on a review of several strands of evidence, including

the GISS melting estimates.

-------
                            - 113 -
                      END NOTES APPENDIX C
_!/   Gornitz, V., S. Lebedeff, and James Hansen, 1982.   "Global
     sea level trend in the past century." Science. 215:26 March;
     1611-4.

_2/   Barnett, Timothy P., 1983. "Global sea level; estimating
     and explaining apparent changes," in Coastal  Zone  '83,
     Orville T. Magoon, editor.  New York: American Society of
     Civil Enginners.  3:2777-84.

-------
                              - 115-
                            BIBLIOGRAPHY
Barnett, Timothy P. [1982]. "Recent changes in sea level and their
    possible causes."  Climate Research Group, Scripps Institution
    of Oceanography, LaJolla, CA.

      	,1983. "Global sea level: estimating and explaining
    apparent changes," in Coastal Zone '83, Orville T. Magoon, editor
    New York: American Society of Civil Engineers. 3:2777-84.

Barnola, J.M., D. Raynaud,  and H. Oeschger, 1983.  "Comparison
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    in polar ice."  Nature  303:2 June:410-13.

Barth, Michael and James Titus, eds. Sea Level Rise to the Year 2100.
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Bell, P.R. 1982. "Methane hydrate and the carbon dioxide question,"
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Bently, Charles R. 1980. "Response of the west Antarctic ice sheet
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          1983. "West Antarctic ice sheet: diagnosis and prognosis,"
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Bloom, Arthur L. 1967.  "Pleistocene shorelines:  a new test of
    isostasy." Geological Society of America Bulletin. 78:1477-1494.

Broecker, Wallace Smith, Tsung-Hung Peng, and R. Engh, 1980.
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Broecker, Wallace Smith, and Tsung-Hung Peng, 1982.  Tracers in
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Brunn, Per. 1962. "Sea level rise as a cause of shore erosion."
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Charney, Jule, et al., 1979.  Carbon Dioxide and Climate;
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-------
                              - 116-
Chylek, Peter and Vvilliam Kellogg, 1982  "The sea level climate
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Clark, J.A., W.E. F'arrell, and W.R. Peltier, 1978. "Global changes in
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