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Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

SURFACE TEMPERATURE RECONSTRUCTIONS FOR THE LAST 2,000 YEARS

Committee on Surface Temperature Reconstructions for the Last 2,000 Years

Board on Atmospheric Sciences and Climate

Division on Earth and Life Studies

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.
www.nap.edu

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

THE NATIONAL ACADEMIES PRESS

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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.

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Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and Medicine


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. Ralph J. Cicerone 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. Wm. 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. Harvey V. Fineberg 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 Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council.

www.national-academies.org

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
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Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

COMMITTEE ON SURFACE TEMPERATURE RECONSTRUCTIONS FOR THE LAST 2,000 YEARS

GERALD R. NORTH (Chair),

Texas A&M University, College Station

FRANCO BIONDI,

University of Nevada, Reno

PETER BLOOMFIELD,

North Carolina State University, Raleigh

JOHN R. CHRISTY,

University of Alabama, Huntsville

KURT M. CUFFEY,

University of California, Berkeley

ROBERT E. DICKINSON,

Georgia Institute of Technology, Atlanta

ELLEN R.M. DRUFFEL,

University of California, Irvine

DOUGLAS NYCHKA,

National Center for Atmospheric Research, Boulder, Colorado

BETTE OTTO-BLIESNER,

National Center for Atmospheric Research, Boulder, Colorado

NEIL ROBERTS,

University of Plymouth, United Kingdom

KARL K. TUREKIAN,

Yale University, New Haven, Connecticut

JOHN M. WALLACE,

University of Washington, Seattle

NRC Staff

IAN KRAUCUNAS, Study Director

CHRIS ELFRING, Board Director

AMANDA STAUDT, Senior Program Officer

ELIZABETH A. GALINIS, Research Associate

LEAH PROBST, Research Associate

DIANE GUSTAFSON, Administrative Coordinator

NORMAN GROSSBLATT, Senior Editor

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

BOARD ON ATMOSPHERIC SCIENCES AND CLIMATE

ROBERT J. SERAFIN (Chair),

National Center for Atmospheric Research, Boulder, Colorado

M. JOAN ALEXANDER,

NorthWest Research Associates/CORA, Boulder, Colorado

FREDERICK R. ANDERSON,

McKenna Long & Aldridge LLP, Washington, D.C.

MICHAEL L. BENDER,

Princeton University, New Jersey

ROSINA M. BIERBAUM,

University of Michigan, Ann Arbor

MARY ANNE CARROLL,

University of Michigan, Ann Arbor

CAROL ANNE CLAYSON,

Florida State University, Tallahassee

WALTER F. DABBERDT,

Vaisala Inc., Boulder, Colorado

KERRY A. EMANUEL,

Massachusetts Institute of Technology, Cambridge

DENNIS L. HARTMANN,

University of Washington, Seattle

PETER R. LEAVITT,

Weather Information Inc., Newton, Massachusetts

JENNIFER A. LOGAN,

Harvard University, Cambridge, Massachusetts

VERNON R. MORRIS,

Howard University, Washington, D.C.

F. SHERWOOD ROWLAND,

University of California, Irvine

THOMAS H. VONDER HAAR,

Colorado State University/CIRA, Fort Collins

ROGER M. WAKIMOTO,

National Center for Atmospheric Research, Boulder, Colorado

Ex Officio Members

ANTONIO J. BUSALACCHI, JR.,

University of Maryland, College Park

ERIC F. WOOD,

Princeton University, New Jersey

NRC Staff

CHRIS ELFRING, Director

PAUL CUTLER, Senior Program Officer

AMANDA STAUDT, Senior Program Officer

MARIA UHLE, Program Officer

IAN KRAUCUNAS, Associate Program Officer

CLAUDIA MENGELT, Associate Program Officer

ELIZABETH A. GALINIS, Research Associate

LEAH PROBST, Research Associate

ROB GREENWAY, Senior Program Assistant

DIANE GUSTAFSON, Administrative Coordinator

ANDREAS SOHRE, Financial Associate

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

Foreword

Our understanding of climate and how it has varied over time is advancing rapidly as new data are acquired and new investigative instruments and methods are employed. Thus in 2005, I suggested to the U.S. Congress that the National Research Council (NRC) could help answer questions about the data and methods that have been used in constructing records of Earth’s surface temperatures from times when there were no scientific instruments, using proxy indicators. How has temperature varied over the last 2,000 years? How certain is the answer to this question?

Subsequently, this study was requested by Representative Sherwood Boehlert, chairman of the Committee on Science, U.S. House of Representatives. Chairman Boehlert asked for a clear and concise report in a relatively short period of time, and the NRC agreed to undertake the study quickly. An ad hoc committee was formed, with the group carefully composed to include the breadth and depth of expertise and perspectives needed to analyze all aspects of how surface temperatures are estimated and interpreted and to comment generally on climate science. The NRC asked the committee to summarize current scientific information on the temperature record for the past two millennia, describe the main areas of uncertainty and how significant they are, describe the principal methodologies used and any problems with these approaches, and explain how central is the debate over the paleoclimate temperature record to the state of scientific knowledge on global climate change.

The committee has prepared a report that, in my view, provides policy makers and the scientific community with a critical view of surface temperature reconstructions and how they are evolving over time, as well as a good sense of how important our understanding of the paleoclimate temperature record is within the overall state of scientific knowledge on global climate change. The report does not make policy recommendations.

I thank the members of the committee, who worked intensely to produce this careful report in a short period of time and contributed much personal time, insight, and energy.

Page viii Cite
Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

The NRC staff and all those who contributed papers, data, graphics, and other information, as well as the independent experts who participated in the rigorous review process, were essential participants.


Ralph J. Cicerone, President

National Academy of Sciences

Chair, National Research Council

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

Preface

This committee was asked to describe and assess the state of scientific efforts to reconstruct surface temperature records for the Earth over approximately the last 2,000 years. (The full Statement of Task appears in Appendix A.) Normally, a technical issue such as surface temperature reconstructions might not generate widespread attention, but this case brings interesting lessons about how science works and how science, especially climate science, is communicated to policy makers and the public. The debate began in 1998 when a paper by Michael Mann, Raymond Bradley, and Malcolm Hughes was published in the journal Nature. The authors used a new methodology to combine data from a number of sources to estimate temperatures in the Northern Hemisphere for the last six centuries and later for the last 1,000 years. This research received wide attention, in part because it was illustrated with a simple graphic, the so-called hockey stick curve, that many interpreted as definitive evidence of anthropogenic causes of recent climate change. The research was given prominence in the 2001 report of the Intergovernmental Panel on Climate Change and then was picked up by many in the wider science community and by the popular media.

Science is a process of exploration of ideas—hypotheses are proposed and research is conducted to investigate. Other scientists work on the issue, producing supporting or negating evidence, and each hypothesis either survives for another round, evolves into other ideas, or is proven false and rejected. In the case of the hockey stick, the scientific process has proceeded for the last few years with many researchers testing and debating the results. Critics of the original papers have argued that the statistical methods were flawed, that the choice of data was biased, and that the data and procedures used were not shared so others could verify the work. This report is an opportunity to examine the strengths and limitations of surface temperature reconstructions and the role that they play in improving our understanding of climate. The reconstruction produced by Dr. Mann and his colleagues was just one step in a long process of research, and it is not (as sometimes presented) a clinching argument for anthropogenic global warming, but rather one of many independent lines of research on global climate change.

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

Using multiple types of proxy data to infer temperature time series over large geographic regions is a relatively new area of scientific research, although it builds upon the considerable progress that has been made in deducing past temperature variations at single sites and local regions. Surface temperature reconstructions often combine data from a number of specialized disciplines, and few individuals have expertise in all aspects of the work. The procedures for dealing with these data are evolving—there is no one “right” way to proceed. It is my opinion that this field is progressing in a healthy manner. As in all scientific endeavors, research reported in the scientific literature is often “work in progress” aimed at other investigators, not always to be taken as individual calls for action in the policy community.

With this as context, the committee considered the voluminous literature pertinent to its charge and received briefings and written contributions from more than two dozen people. We have organized our report knowing that we have at least two different audiences—the science community and the policy community. The principal conclusions of the committee are listed in the Summary and explained in the Overview using nontechnical language. More extensive technical justifications for the committee’s conclusions, including references, are presented in the chapters that follow.

Finally, let me thank the members of the Committee on Surface Temperature Reconstructions for the Last 2,000 Years. The committee worked tirelessly to assess the status of this field of research so that the public can see exactly what is involved, what we currently know about it, and what the prospects are for improving our understanding. We have tried to make clear how this piece of the climate puzzle fits into the broader discussions about global climate change.


Gerald R. North, Chair

Committee on Surface Temperature Reconstructions for the Last 2,000 Years

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

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 National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its 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 wish to thank the following individuals for their review of this report:

David Brillinger, University of California, Berkeley

David Chapman, University of Utah

Julia Cole, University of Arizona

Thomas Crowley, Duke University

Alexander Flax, Independent consultant

Claus Fröhlich, PMOD Technologies

Ricardo Garcia-Herrera, Universidad Complutense de Madrid

Peter Huybers, Woods Hole Oceanographic Institution

Richard Muller, Lawrence Berkeley Laboratory

Robert Stine, University of Pennsylvania

Lonnie Thompson, The Ohio State University

Connie Woodhouse, National Oceanic and Atmospheric Administration

Carl Wunsch, Massachusetts Institute of Technology

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Andrew R. Solow, Woods Hole Oceanographic Institution, and Louis J. Lanzerotti, New

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×

Jersey Institute of Technology. Appointed by the National Research Council, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
×
   

 Lake and Peat Sediments,

 

60

   

 Speleothems,

 

62

   

 Summary,

 

64

6

 

ICE ISOTOPES

 

65

   

 Physical Basis for Deriving Climate Signals from Ice Isotopic Ratio Records,

 

66

   

 Calibration and Resolution,

 

67

   

 Results from Ice Isotopic Ratio Records,

 

67

7

 

GLACIER LENGTH AND MASS BALANCE RECORDS

 

71

   

 Reconstructing Temperature Records from Glacier Records,

 

72

   

 More Detailed Background on Glacier-Length-Based Reconstructions,

 

72

   

 Other Information Available from Glaciers,

 

75

8

 

BOREHOLES

 

77

   

 Boreholes in Rock and Permafrost,

 

78

   

 Limits on Borehole-Based Reconstructions,

 

80

   

 Boreholes in Glacial Ice,

 

81

9

 

STATISTICAL BACKGROUND

 

83

   

 Linear Regression and Proxy Reconstruction,

 

84

   

 Principal Component Regression,

 

89

   

 Validation and the Prediction Skill of the Proxy Reconstruction,

 

92

   

 Quantifying the Full Uncertainty of a Reconstruction,

 

95

10

 

CLIMATE FORCINGS AND CLIMATE MODELS

 

98

   

 Climate Forcings,

 

99

   

 Climate Model Simulations,

 

105

   

 Anthropogenic Forcing and Recent Climate Change,

 

107

11

 

LARGE-SCALE MULTIPROXY RECONSTRUCTION TECHNIQUES

 

110

   

 Evolution of Multiproxy Reconstruction Techniques,

 

111

   

 Strengths and Limitations of Large-Scale Surface Temperature Reconstructions,

 

115

   

 Overall Findings and Conclusions,

 

117

   

 What Comments Can Be Made on the Value of Exchanging Information and Data?,

 

118

   

 What Might Be Done to Improve Our Understanding of Climate Variations Over the Last 2,000 Years?,

 

119

 

 

REFERENCES

 

120

 

 

APPENDIXES

 

 

   

 A  Statement of Task

 

139

   

 B  R Code for Figure 9-2

 

140

   

 C  Biographical Sketches of Committee Members

 

142

Suggested Citation:"Front Matter." National Research Council. 2006. Surface Temperature Reconstructions for the Last 2,000 Years. Washington, DC: The National Academies Press. doi: 10.17226/11676.
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In response to a request from Congress, Surface Temperature Reconstructions for the Last 2,000 Years assesses the state of scientific efforts to reconstruct surface temperature records for Earth during approximately the last 2,000 years and the implications of these efforts for our understanding of global climate change. Because widespread, reliable temperature records are available only for the last 150 years, scientists estimate temperatures in the more distant past by analyzing "proxy evidence," which includes tree rings, corals, ocean and lake sediments, cave deposits, ice cores, boreholes, and glaciers. Starting in the late 1990s, scientists began using sophisticated methods to combine proxy evidence from many different locations in an effort to estimate surface temperature changes during the last few hundred to few thousand years. This book is an important resource in helping to understand the intricacies of global climate change.

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