Reconciling Observations of Global Temperature Change

Panel on Reconciling Temperature Observations

Climate Research Committee

Board on Atmospheric Sciences and Climate

Commission on Geosciences, Environment, and Resources

National Research Councilbreak

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Reconciling Observations of Global Temperature Change Panel on Reconciling Temperature Observations Climate Research Committee Board on Atmospheric Sciences and Climate Commission on Geosciences, Environment, and Resources National Research Councilbreak image

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Page ii 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. Support for this project was provided by the National Oceanic and Atmospheric Administration under Contract No. 50-DKNA-7-90052 and by Alcoa. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the NOAA or any of its sub-agencies or of Alcoa. International Standard Book Number 0-309-06891-6 Additional copies of this report are available from: National Academy Press 2101 Constitution Avenue, NW Box 285 Washington, D.C. 20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area) www.nap.edu Cover: Surface and lower to mid-tropospheric temperature trends for the period 1979–1998. The surface data (left panel) are comprised of surface air temperature over land and the temperature of water at the ocean's surface, and have been subjected to a slight additional smoothing to simplify the pattern (Jones et al., 1999). The lower to mid-tropospheric data (right panel) are derived from satellite observations from the Microwave Sounding Unit Channel 2 (the so-called "MSU 2LT") (Christy et al., 2000). For both datasets, the trends are computed using the method of ordinary least squares. The color key is the same as in Figure 6.2. The map views on the front cover are centered at 30° N and 110° W and the views on the back cover are centered at 30° S and 70° E. For the globe as a whole (see Figures 6.2 and 7.1 inside), warming has been prevalent at the earth's surface, but much less so in the lower to mid-troposphere. Copyright 2000 by the National Academy of Sciences. All rights reserved. Printed in the United States of America First Printing, January 2000 Second Printing, February 2000break

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Page iii THE NATIONAL ACADEMIES National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized 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 advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academics and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.break

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Page v PANEL ON RECONCILING TEMPERATURE OBSERVATIONS Members JOHN M. WALLACE (Chair), University of Washington, Seattle JOHN R. CHRISTY, University of Alabama in Huntsville DIAN J. GAFFEN, NOAA/Air Resources Laboratory, Silver Spring, Maryland NORMAN C. GRODY, NOAA/NESDIS, Camp Springs, Maryland JAMES E. HANSEN, NASA Goddard Institute for Space Studies, New York, New York DAVID E. PARKER, Hadley Centre, Meteorological Office, Bracknell, United Kingdom THOMAS C. PETERSON, NOAA/National Climatic Data Center, Asheville, North Carolina BENJAMIN D. SANTER, Lawrence Livermore National Laboratory, Livermore, California ROY W. SPENCER, NASA Marshall Space Flight Center, Huntsville, Alabama KEVIN E. TRENBERTH, National Center for Atmospheric Research, Boulder, Colorado FRANK J. WENTZ, Remote Sensing Systems, Santa Rosa, California Consultant TODD MITCHELL, University of Washington, Seattle NRC Staff PETER A. SCHULTZ, Study Director DIANE L. GUSTAFSON, Administrative Assistantbreak

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Page vi CLIMATE RESEARCH COMMITTEE Members EUGENE M. RASMUSSON (Chair), University of Maryland, College Park EDWARD S. SARACHIK (Vice-Chair), University of Washington, Seattle MAURICE BLACKMON, National Center for Atmospheric Research, Boulder, Colorado JEFF DOZIER, University of California, Santa Barbara JAMES GIRAYTYS, Consultant, Winchester, Virginia JAMES E. HANSEN, NASA Goddard Institute for Space Studies, New York, New York PHILIP E. MERILEES, Naval Research Laboratory, Monterey, California ROBERTA BALSTAD MILLER, CIESIN, Columbia University, Palisades, New York S. ICHTIAQUE RASOOL, International Consultant, Paris, France STEVEN W. RUNNING, University of Montana, Missoula ANNE M. THOMPSON, NASA Goddard Space Flight Center, Greenbelt, Maryland ANDREW WEAVER, University of Victoria, British Columbia ERIC F. WOOD, Princeton University, New Jersey Ex Officio Members W. LAWRENCE GATES, Lawrence Livermore National Laboratory, Livermore, California DOUGLAS G. MARTINSON, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York JOHN O. ROADS, Scripps Institution of Oceanography, La Jolla, California NRC Staff PETER A. SCHULTZ, Program Director CARTER W. FORD, Project Assistantbreak

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Page vii BOARD ON ATMOSPHERIC SCIENCES AND CLIMATE Members ERIC J. BARRON (Co-Chair), Pennsylvania State University, University Park JAMES R. MAHONEY (Co-Chair), Consultant, McLean, Virginia SUSAN K. AVERY, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder LANCE F. BOSART, State University of New York, Albany MARVIN A. GELLER, State University of New York, Stony Brook CHARLES E. KOLB, Aerodyne Research, Inc., Billerica, Massachusetts ROGER A. PIELKE, JR., National Center for Atmospheric Research, Boulder, Colorado ROBERT T. RYAN, WRC-TV, Washington, D.C. MARK R. SCHOEBERL, NASA Goddard Space Flight Center, Greenbelt, Maryland JOANNE SIMPSON, NASA Goddard Space Flight Center, Greenbelt, Maryland NIEN DAK SZE, Atmospheric and Environmental Research, Inc., Cambridge, Massachusetts ROBERT A. WELLER, Woods Hole Oceanographic Institution, Massachusetts ERIC F. WOOD, Princeton University, New Jersey Ex Officio Members DONALD S. BURKE, Johns Hopkins University, Baltimore, Maryland DARA ENTEKHABI, Massachusetts Institute of Technology, Cambridge MICHAEL C. KELLEY, Cornell University, Ithaca, New York JOHN O. ROADS, Scripps Institution of Oceanography, La Jolla, California EUGENE M. RASMUSSON, University of Maryland, College Park PAUL WINE, Georgia Institute of Technology, Atlanta NRC Staff ELBERT W. (JOE) FRIDAY, JR., Director LAURIE S. GELLER, Program Officerbreak

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Page viii PETER A. SCHULTZ, Program Officer DIANE L. GUSTAFSON, Administrative Assistant ROBIN MORRIS, Financial Associate TENECIA A. BROWN, Senior Program Assistant CARTER W. FORD, Project Assistantbreak

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Page ix COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES Members GEORGE M. HORNBERGER (Chair), University of Virginia, Charlottesville RICHARD A. CONWAY, Union Carbide Corporation (Retired), S. Charleston, West Virginia THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut THOMAS J. GRAFF, Environmental Defense Fund, Oakland, California EUGENIA KALNAY, University, of Maryland, College Park DEBRA KNOPMAN, Progressive Policy Institute, Washington, D.C. KAI N. LEE, Williams College, Williamstown, Massachusetts BRAD MOONEY, J. Brad Mooney Associates, Ltd., Arlington, Virginia HUGH C. MORRIS, El Dorado Gold Corporation, Vancouver, British Columbia H. RONALD PULLIAM, University of Georgia, Athens MILTON RUSSELL, Joint Institute for Energy and Environment and University of Tennessee (Emeritus), Knoxville THOMAS C. SCHELLING, University of Maryland, College Park ANDREW R. SOLOW, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida E-AN ZEN, University of Maryland, College Park MARY LOU ZOBACK, U.S. Geological Survey, Menlo Park, California NRC Staff ROBERT M. HAMILTON, Executive Director GREGORY H. SYMMES, Associate Executive Director JEANETTE SPOON, Administrative and Financial Officer DAVID FEARY, Scientific Reports Officer SANDI FITZPATRICK, Administrative Associate MARQUITA SMITH, Administrative Assistant/Technology Analystbreak

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Page xi ACKNOWLEDGMENTS This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the NRC's Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We thank the following individuals for their participation in the review of this report: JAMES ANGELL, NOAA/Air Resources Laboratory ALAN BASIST, NOAA/National Climatic Data Center LENNART BENGTSSON, Max Planck Institute for Meteorology SIMON BROWN, Hadley Centre, Meteorological Office, United Kingdom JAMES HOLTON, University of Washington JAMES HURRELL, National Center for Atmospheric Research EUGENIA KALNAY, University of Maryland RICHARD LINDZEN, Massachusetts Institute of Technology NEVILLE NICHOLLS, Australian Bureau of Meteorology Research Centre EUGENE M. RASMUSSON, University of Marylandbreak

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Page xii While the individuals listed above have provided constructive comments and suggestions, it must be emphasized that responsibility for the final content of this report rests entirely with the authoring committee and the institution. The panel wishes to thank Todd Mitchell at the University of Washington for his contributions and insight in the presentation of the report's complex data, Jay Lawrimore at the National Climatic Data Center for supplying figures and data, and David Feary at the National Research Council for his editorial guidance.break

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Page xiii PREFACE A National Research Council panel was convened to examine observed trends of temperature near the surface and in the lower to midtroposphere (the atmospheric layer extending from the earth's surface up to about 8 km). The objectives of this panel were to: (1) summarize the state of the science in the measurement of temperature from space, from radiosondes, and from surface instrumentation; (2) assess the biases and uncertainties in the data; (3) describe the major conflicts in the trends; and (4) define the actions required to reduce the uncertainties and biases. The panel, which is under the purview of the Board on Atmospheric Sciences and Climate's (BASC) Climate Research Committee (CRC), included individuals with expertise on all relevant technical facets of the issue. The panel's report, presented here, is structured in a layered fashion, providing the reader with an increasing level of technical detail. The Executive Summary gives a very brief overview of the report's findings and recommendations and is targeted towards non-scientists. Part I of the main body of the report is intended for the public, policy-making, and scientific communities and is also written in a relatively non-technicalcontinue

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Page xiv fashion. Part I includes a chapter outlining the key questions (Introduction) and another that provides an overview of the relevant measurement types and their observations (Background). Part I concludes with chapters on the panel's Findings and Recommendations. Part II more fully articulates the scientific basis for the discussion and conclusions that are presented in Part I, by detailing the major, relevant measurement systems and their temperature records. It does so in chapters on Surface Temperature Observations, MSU Observations, and Radiosonde Observations. Part II concludes with a chapter that compares the temperature records of the three types of observations and presents possible reasons for the observed temperature trend differences.break

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Page xv CONTENTS Executive Summary 1 Part I: Overview and Conclusions 5 1 Introduction 7 2 Background 9 3 Findings 21 4 Recommendations 24 Part II: Technical Background 27 5 Introduction 29 6 Surface Temperature Observations 32 Summary of Trends 32 Sources of Uncertainty in Trend Estimates 36 Efforts to Correct the Problems 38 7 MSU Observations 41 Introduction 41 MSU Temperature Trends 42

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Page xvi Sources of Uncertainty in Trend Estimates 44 8 Radiosonde Observations 50 Summary of Trends 50 Sources of Uncertainty in Trend Estimates 50 Background 51 Data Homogeneity Problems 52 Variety of Methods of Estimating Global Trends in Layer-Mean Temperatures 53 Efforts to Correct the Problems 55 9 Trend Comparisons 58 Comparisons Between MSU and Radiosonde Data sets 58 Evidence Concerning Surface versus Tropospheric Temperature Trends 62 Interpretation of the Differences Between Observed Surface and Tropospheric Temperature Trends 65 Insights Derived from Model Simulations 68 Concluding Remarks 70 References 72 Appendixes 79 A. Biographical Information on Panel Members 81 B. Acronyms and Abbreviations 85