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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
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
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
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
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
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
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
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
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
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
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
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
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
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