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Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Page viii Cite
Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Page xiii Cite
Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

Suggested Citation:"Front Matter." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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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

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An overall increase in global-mean atmospheric temperatures is predicted to occur in response to human-induced increases in atmospheric concentrations of heat-trapping ''greenhouse gases." The most prominent of these gases, carbon dioxide, has increased in concentration by over 30% during the past 200 years, and is expected to continue to increase well into the future. Other changes in atmospheric composition complicate the picture. In particular, increases in the number of small particles (called aerosols) in the atmosphere regionally offset and mask the greenhouse effect, and stratospheric ozone depletion contributes to cooling of the upper troposphere and stratosphere.

Many in the scientific community believe that a distinctive greenhouse-warming signature is evident in surface temperature data for the past few decades. Some, however, are puzzled by the fact that satellite temperature measurements indicate little, if any, warming of the lower to mid-troposphere (the layer extending from the surface up to about 8 km) since such satellite observations first became operational in 1979. The satellite measurements appear to be substantiated by independent trend estimates for this period based on radiosonde data. Some have interpreted this apparent discrepancy between surface and upper air observations as casting doubt on the overall reliability of the surface temperature record, whereas others have concluded that the satellite data (or the algorithms that are being used to convert them into temperatures) must be erroneous. It is also conceivable that temperatures at the earth's surface and aloft have not tracked each other perfectly because they have responded differently to natural and/or human-induced climate forcing during this particular 20-year period. Whether these differing temperature trends can be reconciled has implications for assessing:

  • how much the earth has warmed during the past few decades,
  • whether observed changes are in accord with the predicted response to the buildup of greenhouse gases in the atmosphere based on model simulations, and
  • whether the existing atmospheric observing system is adequate for the purposes of monitoring global-mean temperature.

This report reassesses the apparent differences between the temperature changes recorded by satellites and the surface thermometer network on the basis of the latest available information. It also offers an informed opinion as to how the different temperature records should be interpreted, and recommends actions designed to reduce the remaining uncertainties in these measurements.

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