UNDERSTANDING

Earth’s Deep Past

Lessons for Our Climate Future

Committee on the
Importance of Deep-Time Geologic Records for
Understanding Climate Change Impacts

Board on Earth Sciences and Resources

Division on Earth and Life Studies

NATIONAL RESEARCH COUNCIL
                          OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.

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Committee on the Importance of Deep-Time Geologic Records for Understanding Climate Change Impacts Board on Earth Sciences and Resources Division on Earth and Life Studies THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Gov- erning Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engi - neering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for ap - propriate balance. This study was supported by the National Science Foundation under Grant No. EAR-0625247, the U.S. Geological Survey under Award No. 06HQGR0197, and the Chevron Corporation. The opinions, findings, and conclusions or recommenda - tions contained in this document are those of the authors and do not necessarily reflect the views of the National Science Foundation, the U.S. Geological Survey, or the Chevron Corporation. International Standard Book Number-13: 978-0-309-20915-1 International Standard Book Number-10: 0-309-20915-3 Library of Congress Control Number: 2011930581 Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet www.nap.edu Cover: Cover design by Michael Dudzik. Copyright 2011 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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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 govern- ment 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 en - gineers. 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 engi - neering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest 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 Insti - tute 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 Sci- ences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal govern - ment. Functioning in accordance with general policies determined by the Acad - emy, 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 com - munities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE ON THE IMPORTANCE OF DEEP-TIME GEOLOGIC RECORDS FOR UNDERSTANDING CLIMATE CHANGE IMPACTS ISABEL P. MONTAÑEZ, Chair (2010-2011), University of California, Davis RICHARD D. NORRIS, Chair (2007-2009), Scripps Institution of Oceanography, San Diego, California THOMAS ALGEO, University of Cincinnati, Ohio MARK A. CHANDLER, Columbia University, New York KIRK R. JOHNSON, Denver Museum of Nature and Science, Colorado MARTIN J. KENNEDY, University of Adelaide, South Australia DENNIS V. KENT, Rutgers, The State University of New Jersey, Piscataway JEFFREY T. KIEHL, National Center for Atmospheric Research, Boulder, Colorado LEE R. KUMP, The Pennsylvania State University, University Park A. CHRISTINA RAVELO, University of California, Santa Cruz KARL K. TUREKIAN, Yale University, New Haven, Connecticut Liaison from the Board on Earth Sciences and Resources KATHERINE H. FREEMAN, The Pennsylvania State University, University Park National Research Council Staff DAVID A. FEARY, Study Director NICHOLAS D. ROGERS, Research Associate JENNIFER T. ESTEP, Financial and Administrative Associate COURTNEY R. GIBBS, Program Associate ERIC J. EDKIN, Senior Program Assistant v

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BOARD ON EARTH SCIENCES AND RESOURCES CORALE L. BRIERLEY, Chair, Brierley Consultancy LLC, Denver, Colorado KEITH C. CLARKE, University of California, Santa Barbara DAVID J. COWEN, University of South Carolina, Columbia WILLIAM E. DIETRICH, University of California, Berkeley ROGER M. DOWNS, The Pennsylvania State University, University Park JEFF DOZIER, University of California, Santa Barbara WILLIAM. L. GRAF, University of South Carolina, Columbia RUSSELL J. HEMLEY, Carnegie Institution of Washington, Washington, D.C. MURRAY W. HITZMAN, Colorado School of Mines, Golden EDWARD KAVAZANJIAN, Jr., Arizona State University, Tempe ROBERT B. McMASTER, University of Minnesota, Minneapolis M. MEGHAN MILLER, UNAVCO, Inc., Boulder, Colorado ISABEL P. MONTAÑEZ, University of California, Davis CLAUDIA INÉS MORA, Los Alamos National Laboratory, New Mexico BRIJ M. MOUDGIL, University of Florida, Gainesville CLAYTON R. NICHOLS, Idaho National Engineering and Environmental Laboratory (retired), Ocean Park, Washington HENRY N. POLLACK, University of Michigan, Ann Arbor JOAQUIN RUIZ, University of Arizona, Tucson PETER M. SHEARER, University of California, San Diego, La Jolla REGINAL SPILLER, Allied Energy, Texas RUSSELL E. STANDS-OVER-BULL, Anadarko Petroleum Corporation, Billings, Montana TERRY C. WALLACE, Jr., Los Alamos National Laboratory, New Mexico National Research Council Staff ANTHONY R. De SOUZA, Director ELIZABETH A. EIDE, Senior Program Officer DAVID A. FEARY, Senior Program Officer ANNE M. LINN, Senior Program Officer MARK D. LANGE, Program Officer SAMMANTHA L. MAGSINO, Program Officer JENNIFER T. ESTEP, Financial and Administrative Associate NICHOLAS D. ROGERS, Financial and Research Associate COURTNEY R. GIBBS, Program Associate JASON R. ORTEGO, Research Associate ERIC J. EDKIN, Senior Program Assistant CHANDA IJAMES, Program Assistant vi

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Preface The drive to better understand how Earth’s climate has responded to natural and anthropogenic forcing over the geologically recent past has resulted in a plethora of observational and modeling paleoclimate studies seeking to understand climate dynamics associated with glacial and inter- glacial cyclicity. From these near-time paleoclimate studies the scientific community has developed a refined understanding of the complex—and often nonlinear—dynamics of the Earth’s climate system and has delin - eated an array of environmental and ecological impacts that have accom - panied climate change over the past few thousands to hundreds of thou- sands of years. The knowledge gleaned from this near-time archive has been of great importance for predicting Earth’s immediate future climate. There is, however, a growing appreciation by the scientific community that the changes observed over the past few decades may lead to a degree of warming and associated climate, resource, and ecological changes well beyond those of the “icehouse” climate state in which humans evolved and currently live. Critical insights to understanding such changes are contained in the deep-time geological record that captures the response of the climate system to the full spectrum of internal and external forcings, and their feedbacks, experienced over Earth history. There is little dispute within the scientific community that humans are changing Earth’s climate on a decadal to century timescale. This change, however, is happening within the context of geological time and geological magnitude, and thus must be evaluated and understood at a comparable scale. The fossil fuel CO2 released to the atmosphere by humans will impact the climate system for tens to hundreds of thousands of years, vii

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viii PREFACE because of the timescales over which the natural feedbacks in the climate system sweep CO2 from the atmosphere. Consequently, the changes to the hydrosphere, cryosphere, chemosphere, and biosphere that are occurring now and projected within this century could pale in comparison to those that are possible over the next few centuries. Furthermore, it is studies of deep-time climates that have revealed the nature of the complex network of short- and long-term processes and feedbacks that govern the global cli- mate system. Perhaps more importantly, these studies have also revealed the potential for positive feedbacks that typically operate on century to millennial timescales but may become operative on much shorter, human timescales with continued warming. There are important lessons to be learned from the repeated inability of existing climate models to recre- ate the large changes in global temperature distributions and climates that can be deciphered from deep-time records of past climates that were much different than Earth’s current glacial state. Despite its potential, the deep-time geological record is undertapped scientifically, particularly because it hosts the only records of major, and at times rapid, transitions across climate states as well as records of past warming far greater than witnessed by Earth over the past few tens of millions of years but within the scope of that projected for our future. This report is the committee’s collective assessment of both the dem - onstrated and the underdeveloped potential of the deep-time geological record to inform us about the dynamics of the global climate system in response to the spectrum of forcings and conditions under which it has operated. A large part of our effort was directed toward describing past climate changes and their impacts on regional climates, water resources, marine and terrestrial ecosystems, and the cycling of life-sustaining ele - ments, emphasizing the lessons that have been learned uniquely from deep-time worlds. While revealing gaps in scientific knowledge of past climate states, we highlight a range of high-priority scientific issues with potential for major advances in the scientific understanding of climate processes. Understanding how the complex network of processes and feedbacks that make up the global climate system operates at various timescales—and over the full range of climate variability experienced through Earth’s history—is a high priority for improving projections of future climatic conditions and the impacts on the surface systems that can be anticipated with such change. To that end, we propose a research agenda—and an implementation strategy to address this agenda—that builds on the evolving cross- and interdisciplinary nature of deep-time paleoclimate science. As the question is increasingly raised as to whether Earth could return—on a human timescale—to a greenhouse climate analogous to that of more than 35 million years ago, it is essential that science thoroughly

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ix PREFACE understands the mechanisms, triggers, and thresholds of climate change in past warmer worlds and the associated magnitudes, rates, and impacts of such change. We hope that the readers of this report share our collective enthusiasm for the richness and societal relevance of the geological record and for the exciting opportunities for enhanced knowledge provided by deep-time paleoclimatology. The committee would like to thank the National Science Foundation, the U.S. Geological Survey, and Chevron Corporation for enabling this report through their financial support and participation in the study pro - cess. As chair, I would also like to acknowledge the committee members for the insights they brought to the table and their efforts in translating a plentitude of knowledge into lucid statements and informative fig- ures. The process was not always linear and involved crossing multiple thresholds; but analogous to climate change, we anticipate that the out - come of the process, this report, will “impact” scientific understanding of the potential of Earth’s global climate system for change. Study Director David Feary deserves a special acknowledgment for his tireless effort and patience, aptitude for skillful persuasion, and wonderful wit—it was a privilege to work with him. The committee is also grateful for the support of National Research Council staff members Nicholas Rogers, Courtney Gibbs, and Eric Edkin. Isabel Patricia Montañez, Chair Committee on the Importance of Deep-Time Geologic Records for Understanding Climate Change Impacts

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Acknowledgments This report was greatly enhanced by those who made presentations to the committee at public committee meetings and by the participants at the open workshop sponsored by the committee to gain community input—David Beerling, Ray Bernor, Karen Bice, Scott Borg, Gabriel Bowen, Robert DeConto, Harry Dowsett, Alexey Federov, Chris Fielding, Margaret Frasier, Linda Gundersen, Bill Hay, Patricia Jellison, H. Richard Lane, Tim Lyons, Thomas Moore, Paul Olsen, Mark Pagani, Judy Parrish, Martin Perlmutter, Chris Poulsen, Greg Ravizza, Dana Royer, Nathan Sheldon, Walt Snyder, Linda Sohl, Lynn Soreghan, Christopher Swezey, Robert Thompson, Thomas Wagner, Debra Willard, Scott Wing, James Zachos, and Richard Zeebe. The presentations and discussions at these meetings provided invaluable input and context for the committee’s deliberations. The provision of additional text and figures by Ron Blakey, Paul Olsen, Shanan Peters, Brad Sageman, Lynn Soreghan, Jim Zachos, and Richard Zeebe is also gratefully acknowledged. 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 participation in the review of this report: xi

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xii ACKNOWLEDGMENTS Ken Caldeira, Carnegie Institution of Washington, Stanford, California Christopher R. Fielding, University of Nebraska, Lincoln Paul E. Olsen, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York Heiko Pälike, National Oceanography Centre, University of Southampton, United Kingdom Christopher J. Poulsen, University of Michigan, Ann Arbor Bradley B. Sageman, Northwestern University, Evanston, Illinois Linda E. Sohl, NASA Goddard Institute for Space Studies, Columbia University, New York Thomas N. Taylor, University of Kansas, Lawrence Ellen Thomas, Yale University, New Haven, Connecticut James C. Zachos, University of California, Santa Cruz Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclu - sions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by William W. Hay, University of Colorado Museum, and Peter M. Banks, Executive Office, National Academy of Sciences, Washington, D.C. 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.

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Contents EXECUTIVE SUMMARY 1 SUMMARY 5 1 INTRODUCTION 16 Committee Charge and Scope of This Study, 24 2 LESSONS FROM PAST WARM WORLDS 26 Climate Sensitivity to Increasing CO2 in a Warmer World, 29 Tropical and Polar Climate Stability and Latitudinal Temperature Gradients in a Warmer World, 33 Hydrological Processes and the Global Water Cycle in a Warmer World, 36 Sea Level and Ice Sheet Fluctuations in a Warmer World, 40 Expansion of Oceanic Hypoxia in a Warmer World, 45 Biotic Response to a Warmer World, 51 3 CLIMATE TRANSITIONS, TIPPING POINTS, AND THE POINT OF NO RETURN 63 Icehouse-Greenhouse Transitions, 65 How Long Will the Greenhouse Last? 76 xiii

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xiv CONTENTS 4 DECIPHERING PAST CLIMATES—RECONCILING MODELS AND OBSERVATIONS 81 Climate Model Capabilities and Limitations, 86 Indicators of Climate Sensitivity Through Time—Proxies for CO2 and Marine Temperatures, 92 Indicators of Regional Climates, 100 Indicators of Oceanic pH and Redox, 104 5 IMPLEMENTING A DEEP-TIME CLIMATE RESEARCH AGENDA 106 Elements of a High-Priority Deep-Time Climate Research Agenda, 107 Strategies and Tools to Implement the Research Agenda, 113 Education and Outreach—Steps Toward a Broader Community Understanding of Climates in Deep Time, 131 6 CONCLUSIONS AND RECOMMENDATIONS 138 Strategies and Tools to Implement a Deep-Time Climate Research Agenda, 143 Education and Outreach—Steps Toward a Broader Community Understanding of Climates in Deep-Time, 146 REFERENCES 149 APPENDIXES A Committee Biographical Sketches 181 B Workshop Agenda and Participants 185 C Presentations to Committee 192 D Acronyms and Abbreviations 193