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Carbon Dioxide and Climate: A Second Assessment Report of the CC>2/Clinnate Review Panel to the Climate Research Committee of the Climate Board/Committee on Atmospheric Sciences and the Carbon Dioxide Assessment Committee of the Climate Board Commi'ssion on Physical Sciences, Mathematics, and Resources LIBRARY National Research Council National Research Council 2101 Constitution Avenue N.WÂ» Washington B.C. 20418 ufu-f noni Nationai Technical information ServId. NATIONAL ACADEMY PRESS SpringfieId, V4, Washington, D.C. 1982 22161 â Order Ho.
NOTICE The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. Library of Congress Cataloging in Publication Data National Research Council (U.S.). CO,/Climate Review Panel. Carbon dioxide and climate. Bibliography: p. 1. Atmospheric carbon dioxideâResearchâUnited States. 2. United StatesâClimate. I. National Research Council (U.S.). Climate Research Committee. II. National Research Council (U.S.). Climate Board. Carbon Dioxide Assessment Committee. III. Title. QC879.8.N37 1982 551.6 82-12445 ISBN 0-309-03285-7 Available from NATIONAL ACADEMY PRESS 2101 Constitution Avenue, N.W. Washington, D.C. 20418 Printed in the United States of America
COo/Climate Review Panel Joseph Smagorinsky, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Chairman Laurence Armi, Scripps Institution of Oceanography Francis P. Bretherton, National Center for Atmospheric Research Kirk Bryan, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration Robert D. Cess, State University of New York, Stony Brook W. Lawrence Gates, Oregon State University James Hansen, Goddard Institute for Space Studies, National Aeronautics and Space Administration John E. Kutzbach, University of Wisconsin, Madison Syukuro Manabe, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration Invited Experts William W. Kellogg, National Center for Atmospheric Research V. Ramanathan, National Center for Atmospheric Research Stephen H. Schneider, National Center for Atmospheric Research Staff John S. Perry, National Research Council, Executive Secretary Robert S. Chen, National Academy of Sciences, Resident Fellow iii
Climate Research Committee Joseph Smagorinsky, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Chairman D. James Baker, Jr., University of Washington Tim P. Barnett, Scripps Institution of Oceanography Harry L. Bryden, Woods Hole Oceanographic Institution W. Lawrence Gates, Oregon State University John E. Kutzbach, University of Wisconsin, Madison Syukuro Manabe, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration Allan R. Robinson, Harvard University Thomas H. Yonder Haar, Colorado State University John M. Wallace, University of Washington Gunter E. Weller, University of Alaska
Carbon Dioxide Assessment Committee William A. Nierenberg, Scripps Institution of Oceanography, Chairman Peter G. Brewer, National Science Foundation Lester Machta, Air Resources Laboratory, National Oceanic and Atmo- spheric Administration William D. Nordhaus, Yale University Roger R. Revelle, University of California, San Diego Thomas C. Schelling, Harvard University Joseph Smagorinsky, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration Paul E. Waggoner, Connecticut Agricultural Experiment Station George M. Woodwell, Marine Biological Laboratory vil
Committee on Atmospheric Sciences Richard J. Reed, University of Washington, Chairman Verner E. Suomi, University of Wisconsin, Madison, Vice Chairman David Atlas, National Aeronautics and Space Administration Ferdinand Baer, University of Maryland Ralph J. Cicerone, National Center for Atmospheric Research Robert E. Dickinson, National Center for Atmospheric Research John A. Dutton, Pennsylvania State University John V. Evans, Massachusetts Institute of Technology Peter V. Hobbs, University of Washington T. N. Krishnamurti, Florida State University James C. Me Williams, National Center for Atmospheric Research F. Sherwood Rowland, University of California, Irvine Frederick Sanders, Massachusetts Institute of Technology Friedrich Schott, University of Miami Liaison with Federal Agencies Richard S. Greenfield, National Science Foundation Ronald L. Lavoie, National Oceanic and Atmospheric Administration Staff Fred D. White, Executive Secretary ix
Climate Board Verner E. Suomi, University of Wisconsin, Madison, Chairman Philip Abelson, American Association for the Advancement of Science William C. Ackermann, University of Illinois at Urbana-Champaign Werner A. Baum, Florida State University Francis P. Bretherton, National Center for Atmospheric Research Dayton H. Clewell, Darien, Connecticut Thomas M. Donahue, University of Michigan Joseph O. Fletcher, National Oceanic and Atmospheric Administration Robert W. Kates, Clark University John E. Kutzbach, University of Wisconsin, Madison Estella B. Leopold, University of Washington William A. Nierenberg, Scripps Institution of Oceanography Roger R. Revelle, University of California, San Diego Joseph Smagorinsky, National Oceanic and Atmospheric Administration Sylvan H. Wittwer, Michigan State University Warren S. Wooster, University of Washington Staff John S. Perry, National Research Council, Executive Secretary Robert S. Chen, National Academy of Sciences, Resident Fellow xi
xii Climate Board Liaison with Federal Agencies Eugene W. Bierly, National Science Foundation Alan D. Hecht, National Climate Program Office Norman L. Canfield, National Oceanic and Atmospheric Administration Galen Hart, Department of Agriculture Gerald J. Kovach, Committee on Commerce, Science and Transportation, U.S. Senate David W. McClintock, Department of State Lloyd J. Money, Department of Transportation Robert E. Palmer, U.S. House of Representatives George I. Smith, Department of the Interior Joel A. Snow, Department of Energy Shelby G. Tilford, National Aeronautics and Space Administration Paul D. Try, Department of Defense Herbert L. Wiser, Environmental Protection Agency
Commission on Physical Sciences, Mathematics, and Resources Herbert Friedman, National Research Council, Cochairman Robert M. White, University Corporation for Atmospheric Research, Cochairman Stanley I. Auerbach, Oak Ridge National Laboratory Elkan R. Blout, Harvard Medical School William Browder, Princeton University Bernard F. Burke, Massachusetts Institute of Technology Herman Chernoff, Massachusetts Institute of Technology Walter R. Eckelmann, Exxon Corporation Joseph L. Fisher, Office of the Governor, Commonwealth of Virginia James C. Fletcher, University of Pittsburgh William A. Fowler, California Institute of Technology Gerhart Friedlander, Brookhaven National Laboratory Edward A. Frieman, Science Applications, Inc. Edward D. Goldberg, Scripps Institution of Oceanography Konrad B. Krauskopf, Stanford University Charles J. Mankin, Oklahoma Geological Survey Walter H. Munk, University of California, San Diego Norton Nelson, New York University Medical Center Daniel A. Okun, University of North Carolina George E. Pake, Xerox Research Center David Pimentel, Cornell University Charles K. Reed, National Research Council Hatten S. Yoder, Jr., Carnegie Institution of Washington Raphael G. Kasper, Acting Executive Director xiii
Foreword As residents of this most pleasant planet, we must necessarily be concerned about any changes in its heating and ventilation systems. One possibly significant change has been unequivocally observed over the past two decades: the amount of carbon dioxide in the air has increased. Moreover, it seems almost certain that we are primarily to blame. By burning fossil fuels and converting the carbon-rich natural landscape into farmland and cities, we transfer carbon to the atmosphere. Since carbon dioxide absorbs and emits thermal radiation and is an essential nutrient for plants, there is good reason to suspect that increases in its abundance may affect the climate of the globe and the workings of the biological systems that support our life. As we plan ways of meeting our energy needs from fossil fuel and al- ternative sources, it is thus prudent to consider the implications for atmospheric carbon dioxide, climate, agriculture, the natural biosphere, and indeed for our increasingly interdependent global society. In framing the Energy Security Act of 1980, the Congress requested the Office of Science and Technology Policy and the National Academy of Sciences to conduct a comprehensive assessment of the implications of increasing carbon dioxide due to fossil fuel use and other human activities. The Climate Board of the National Research Council was asked to assume responsibility for the study, and the Carbon Dioxide Assessment Committee was formed under the board's aegis. Our assessment will deal with many questions relating to this complex issue: What amounts of fossil fuel are likely to be burned? How much carbon dioxide may remain in the air? What may be the effects on agriculture? How may these changes interact with other changes in a rapidly evolving world? xv
xvi Foreword At this writing, work is under way on these and other elements that will be integrated into our report. It was evident, however, that one aspect of the carbon dioxide issue merited early attention. The influence of higher levels of atmospheric carbon dioxide on climate was assessed in 1979 by a panel chaired by the late Me G. Charney. Since then, much work has been done, and some questions have been raised. An updated assessment of the relationship between carbon dioxide and climate was clearly in order, and Joseph Smagorinsky, Director of the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration, was requested to lead a panel to address this task. This is the panel's report. It will contribute to the assessment to be prepared by the Carbon Dioxide Assessment Committee, but it also stands in its own right as a significant addition to our understanding of this complex and worrisome issue. I believe that it should also serve as a continuing reminder of the genius and wisdom of Me G. Charney, who illuminated this question as he did so many other problems of science and mankind. William A. Nierenberg, Chairman Carbon Dioxide Assessment Committee
Preface In the summer of 1979, the Director of the Office of Science and Technology Policy (OSTP) requested the President of the National Academy of Sciences to conduct a special study to assess the then current state of knowledge regarding the possible effects of increased atmospheric carbon dioxide (CO2) on climate. A committee under the chairmanship of the late Jule G. Charney was formed and produced a report (Climate Research Board, 1979), hereafter referred to as the Charney report. In the intervening years, the National Research Council (NRC) formed the Carbon Dioxide Assessment Committee under its Climate Board (formerly the Climate Research Board). The committee's responsibility to the OSTP, at the request of the Congress, is to provide an overview of the entire CO2 question. In this pursuit, the Carbon Dioxide Assessment Committee has asked the Climate Research Committee of the Climate Board (CB) and the Committee on Atmospheric Sciences (CAS) to bring up to date the Charney report, while essentially retaining the focus confined to the CO2-climate connection. The timeliness of such an update stems from the accelerated research activity on the many facets of the problem stimulated by vigorous national and international public attention. The subjects covered in the present report, therefore, generally coincide with those in the 1979 report, but some new considerations have been included, reflecting a broadened base of understanding of the problem. Examples are the role of aerosols, the development of climate scenarios, and some issues relating to development of a monitoring strategy for early detection. The present ad hoc CO2/Climate Review Panel, including invited experts, was established by the joint CB/CAS Climate Research Committee. Three xvii
xviii Preface meetings of the panel were held in March, April, and July 1981. The last of these took place at the National Center for Atmospheric Research, and we appreciate greatly the center's hospitality and the opportunity for discussions with its expert research staff. Staff support for the panel's work was provided by Robert S. Chen and John S. Perry of the CB staff, and Doris Bouadjemi and Sally Larisch speedily processed innumerable corrections and interim drafts. The panel is most grateful for the contributions of the invited experts who assisted in its work and are cited in the list of its members. In particular, V. Ramanathan and Stephen H. Schneider made major contributions to the discussion of energy-balance models. The panel's draft report was reviewed by members of the original Charney panel, other experts, the panel's parent committees, and the NRC'S Report Review Committee. The report discusses at length two recent studies that have concluded that the effect of increased CO2 on surface temperatures will be much less than estimated by the majority of the scientific community. The panel believes that these studies are flawed and incomplete, and the report attempts to identify clearly their deficiencies. The authors of the dissenting studies were provided with an opportunity to review the panel's report but remain unconvinced. Ultimately, of course, nature will reveal to us all the truth. The panel believes that, with the rapid rate of development of some of the scientific foundations on which firmer conclusions can be drawn, the problem will warrant periodic reassessments. Joseph Smagorinsky, Chairman COi/Climate Review Panel
Contents SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS 1 1 INTRODUCTION AND OVERVIEW 9 2 PRINCIPAL SCIENTIFIC ISSUES IN MODELING STUDIES 15 Global Climate SensitivityâSimplified Models and Empirical Approaches, 15 One-dimensional models, 15 Surface energy balance considerations, 17 Models of the Earth's complete energy balance, 17 Dissenting inferences from energy-balance models and empirical studies, 18 Role of the Oceans, 24 Role of the ocean in the transient response of climate, 24 Effects of sea ice, 30 Cloud Effects, 31 Cloudiness-radiation feedback, 31 Stratus-sea-ice interactions, 33 Trace Gases Other Than CO2, 34 Atmospheric Aerosols, 37 Validation of Climate Models, 39 Need for model validation, 39 Present state of model validation, 40 xix
xx Contents Planetary studies, 43 Alternative modeling approaches, 45 Improvement of model validation, 46 3 PREDICTIONS AND SCENARIOS OF CLIMATE CHANGES DUE TO CO, INCREASES 48 Development of Predictions and Scenarios, 48 Model Studies, 50 Numerical experiments with climate models, 50 Global-average response, 50 Zonal-average response, 53 Geographical distribution of climate changes, 55 Observational Studies of Contemporary and Past Climates, 56 Use of observational studies, 56 Contemporary climatic data, 56 Past climatic data, 58 4 DEVELOPMENT OF MONITORING AND EARLY DETECTION STRATEGIES 61 Current Status, 61 Detection Strategies, 61 Monitoring Ocean Climate Response, 63 REFERENCES 65