ABRUPT IMPACTS
OF CLIMATE CHANGE

ANTICIPATING SURPRISES

Committee on Understanding and Monitoring
Abrupt Climate Change and its Impacts

Board on Atmospheric Sciences and Climate

Division on Earth and Life Studies

NATIONAL RESEARCH COUNCIL
             OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

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ABRUPT IMPACTS OF CLIMATE CHANGE A N T ICIPATING S U R P R I S E S Committee on Understanding and Monitoring Abrupt Climate Change and its Impacts Board on Atmospheric Sciences and Climate Division on Earth and Life Studies

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THE NATIONAL ACADEMIES PRESS  •  500 Fifth Street, NW  •  Washington, DC 20001 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. This study was supported by the National Oceanic and Atmospheric Administration under con- tract number WC133R-11-CQ-0048, TO#3, the National Science Foundation under grant num- ber EAR-1305802, the United States intelligence community, and the National Academies. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the sponsoring agencies or any of their subagencies. International Standard Book Number-13:  978-0-309-28773-9 International Standard Book Number-10:  0-309-28773-1 Library of Congress Control Number:  2013957745 Additional copies of this report are available for sale from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap. edu/. Copyright 2013 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 distin- guished 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 Na- tional 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. C. D. Mote, Jr., is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to se- cure 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 educa- tion. 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 fur- thering 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. Cice- rone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE ON UNDERSTANDING AND MONITORING ABRUPT CLIMATE CHANGE AND ITS IMPACTS JAMES W.C. WHITE (Chair), University of Colorado, Boulder RICHARD B. ALLEY, Pennsylvania State University, University Park DAVID E. ARCHER, University of Chicago, IL ANTHONY D. BARNOSKY, University of California, Berkeley JONATHAN FOLEY, University of Minnesota, Saint Paul RONG FU, University of Texas, Austin MARIKA M. HOLLAND, National Center for Atmospheric Research, Boulder, CO M. SUSAN LOZIER, Duke University, Durham, NC JOHANNA SCHMITT, University of California, Davis LAURENCE C. SMITH, University of California, Los Angeles GEORGE SUGIHARA, University of California, San Diego DAVID W. J. THOMPSON, Colorado State University, Fort Collins ANDREW J. WEAVER, University of Victoria, British Columbia STEVEN C. WOFSY, Harvard University, Cambridge, MA NRC Staff EDWARD DUNLEA, Senior Program Officer CLAUDIA MENGELT, Senior Program Officer AMANDA PURCELL, Research Associate ROB GREENWAY, Program Associate v

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BOARD ON ATMOSPHERIC SCIENCES AND CLIMATE ANTONIO J. BUSALACCHI, JR. (Chair), University of Maryland, College Park GERALD A. MEEHL (Vice Chair), National Center for Atmospheric Research, Boulder, Colorado LANCE F. BOSART, State University of New York, Albany MARK A. CANE, Columbia University, Palisades, NY SHUYI S. CHEN, University of Miami, FL HEIDI CULLEN, Climate Central, Princeton, NJ PAMELA EMCH, Northrup Grumman Aerospace Systems, Redondo Beach, CA WILLIAM B. GAIL, Global Weather Corporation, Boulder, CO LISA GODDARD, Columbia University, Palisades, NY TERRI S. HOGUE, Colorado School of Mines, Golden ANTHONY JANETOS, Boston University RONALD “NICK” KEENER, JR., Duke Energy Corporation, Charlotte, NC JOHN E. KUTZBACH, University of Wisconsin, Madison STEPHEN W. PACALA, Princeton University, NJ ARISTIDES A.N. PATRINOS, New York University, Brooklyn RAYMOND T. PIERREHUMBERT, The University of Chicago, IL KIMBERLY PRATHER, University of California, San Diego S.T. RAO, North Carolina State University, Raleigh DAVID A. ROBINSON, Rutgers, The State University of New Jersey, Piscataway JOHN T. SNOW, The University of Oklahoma, Norman CLAUDIA TEBALDI, Climate Central, Princeton, NJ XUBIN ZENG, University of Arizona, Tucson Ocean Studies Board Liaison DANIEL RUDNICK, University of California, San Diego NRC Staff AMANDA STAUDT, Director EDWARD DUNLEA, Senior Program Officer LAURIE GELLER, Senior Program Officer KATIE THOMAS, Associate Program Officer LAUREN BROWN, Associate Program Officer AMANDA PURCELL, Research and Financial Associate RITA GASKINS, Administrative Coordinator ROB GREENWAY, Program Associate SHELLY FREELAND, Senior Program Assistant vi

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Preface C limate is changing, forced out of the range of the last million years by levels of carbon dioxide and other greenhouse gases not seen in Earth’s atmosphere for a very long time. Lacking action by the world’s nations, it is clear that the planet will be warmer, sea level will rise, and patterns of rainfall will change. But the future is also partly uncertain—there is considerable uncertainty about how we will arrive at that different climate. Will the changes be gradual, allowing natural systems and soci- etal infrastructure to adjust in a timely fashion? Or will some of the changes be more abrupt, crossing some threshold or “tipping point” to change so fast that the time be- tween when a problem is recognized and when action is required shrinks to the point where orderly adaptation is not possible? A study of Earth’s climate history suggests the inevitability of “tipping points”— thresholds beyond which major and rapid changes occur when crossed—that lead to abrupt changes in the climate system. The history of climate on the planet—as read in archives such as tree rings, ocean sediments, and ice cores—is punctuated with large changes that occurred rapidly, over the course of decades to as little as a few years. There are many potential tipping points in nature, as described in this report, and many more that we humans create in our own systems. The current rate of carbon emissions is changing the climate system at an accelerating pace, making the chances of crossing tipping points all the more likely. The seminal 2002 National Academy Re- port, Abrupt Climate Changes: Inevitable Surprises (still required reading for anyone with a serious interest in our future climate) was aptly named: surprises are indeed inevi- table. The question is now whether the surprises can be anticipated, and the element of surprise reduced. That issue is addressed in this report. Scientific research has already helped us reduce this uncertainty in two important cases; potential abrupt changes in ocean deep water formation and the release of carbon from frozen soils and ices in the polar regions were once of serious near-term concern are now understood to be less imminent, although still worrisome as slow changes over longer time horizons. In contrast, the potential for abrupt changes in ecosystems, weather and climate extremes, and groundwater supplies critical for agri- culture now seem more likely, severe, and imminent. And the recognition that a gradu- ally changing climate can push both natural systems, as well as human systems, across tipping points has grown over the past decade. This report addresses both abrupt vii

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P R E FA C E climate changes in the physical climate system, and abrupt climate impacts that occur in human and natural systems from a steadily changing climate. In addition to a changing climate, multiple other stressors are pushing natural and human systems toward their limits, and thus become more sensitive to small perturba- tions that can trigger large responses. Groundwater aquifers, for example, are being depleted in many parts of the world, including the southeast of the United States. Groundwater is critical for farmers to ride out droughts, and if that safety net reaches an abrupt end, the impact of droughts on the food supply will be even larger. Must abrupt changes always be surprises? Certainly not. As knowledge of the tipping points in natural and human systems improves, an early warning system can be devel- oped. Careful and vigilant monitoring, combined with a constantly improving scientific understanding of the climate system, can help society to anticipate major changes before they occur. But it is also important to carefully and vigilantly catalog the assets at risk—societies cannot protect everything and will need to prioritize, and without an understanding of what could be lost, such as coastal infrastructure to rising seas, for example, intelligent decisions about what to protect first cannot be made. Can all tipping points be foreseen? Probably not. Some will have no precursors, or may be triggered by naturally occurring variability in the climate system. Some will be dif- ficult to detect, clearly visible only after they have been crossed and an abrupt change becomes inevitable. Imagine an early European explorer in North America, paddling a canoe on the swift river. This river happens to be named Niagara, but the paddler does not know that. As the paddler approaches the Falls, the roar of the water goes from faint to alarming, and the paddler desperately tries to make for shore. But the water is too swift, the tipping point has already been crossed, and the canoe—with the paddler—goes over the Falls. This tipping point is certainly hard to anticipate, but is it inevitable? No. The tipping point in this case could have been detected by an early warning system (listening for the roar of a waterfall), but importantly, prudence was re- quired. Sticking closer to shore, in other words taking some prudent precautions, could have saved the paddler. Precaution will help us today as well, as we face a changing climate, if we are prudent enough to exercise it. Key to this is the need to be watching and listening for the early warning signals. I would like to commend the committee for their hard work, stimulating conversa- tions, scientific expertise, and most importantly, willingness to think outside of the box and take a fresh look at this issue. To Richard Alley (he of the 2002 Report), David Archer, Tony Barnosky, Jon Foley, Rong Fu, Marika Holland, Susan Lozier, Annie Schmitt, Larry Smith, George Sugihara, David Thompson, The Honorable Andrew Weaver and Steve Wofsy, I owe great thanks and heaps of praise. This report was an adventure, viii

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Preface and I could not have asked for better travelling companions. The staff of the National Research Council, those heroes behind the scenes, worked tirelessly to make this study a success. Rob Greenway and Amanda Purcell spent countless hours pulling together text and organizing meetings. Claudia Mengelt contributed valuable discussions and tight editing. And Edward Dunlea simply did it all, keeping me and the rest of the crew on track, ensuring that we could indeed get this done in the time allotted (never enough, it seems) and making sure it all came together. To the committee and staff, my deep, heartfelt thanks; intelligent, hard-working and industrious folks all. In fact, we have a planet full of intelligent, hard-working and industrious folks. Humans are capable of solving whatever problems nature throws at us, or that we create. But first we have to arm ourselves with information and then commit to using that information intelligently and wisely, and that, in a nutshell, is the message of this report. Jim White, Chair Committee on Understanding and Monitoring Abrupt Climate Change and its Impacts ix

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Acknowledgments T his 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 (NRC’s) Report Review Committee. The pur- pose 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 responsive- ness to the study charge. The review comments and draft manuscript remain confi- dential to protect the integrity of the deliberative process. The committee wishes to thank the following individuals for their review of this report: PETER BREWER, Monterey Bay Aquarium Research Institute, Moss Landing, CA ANTHONY JANETOS, Boston University, Massachusetts JAMES KIRTLEY, Massachusetts Institute of Technology, Cambridge, MA TIMOTHY LENTON, University of Exeter, UK MARK PAGANI, Yale University, New Haven, CT J.R. ANTHONY PEARSON, Schlumberger Cambridge Research, Cambridge, UK DOROTHY PETEET, NASA Goddard / Columbia LDEO, Palisades, NY ROGER PULWARTY, National Oceanic and Atmospheric Administration, Boulder, CO PETER RHINES, University of Washington, Seattle RICHARD L. SMITH, University of North Carolina, Chapel Hill WILLIAM TRAVIS, University of Colorado, Boulder GEORGE WOODWELL, Woods Hole Research Center, Massachusetts Although the reviewers listed above have provided constructive comments and sug- gestions, they were not asked to endorse the views of the committee, nor did they see the final draft of the report before its release. The review of this report was over- seen by Marc Levy, Columbia University, Palisades, NY, and Warren M. Washington, National Center for Atmospheric Research, Boulder, CO, appointed by the NRC Report Review Committee, who 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 panel and the institution. xi

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ACKNOWLEDGMENTS In addition, the committee would like to thank the following individuals for their help- ful discussions throughout the study process: Waleed Abdalati, Peter Brewer, Wally Broecker, Edward Dlugokencky, Ian Eismann, James Famiglietti, Jennifer Francis, Sherri Goodman, James Hansen, Paul Harnik, Stephen Jackson, Ian Joughin, David Lobell, Keith Moore, Ray Pierrehumbert, Lorenzo Polvani, William Reeburgh, Gabriel Vecchi, and Scott Wing. xii

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Contents Summary 1 State of Knowledge on Abrupt Impacts of Climate Change, 2 Anticipating Surprises, 15 The Way Forward, 17 1 Introduction 19 Previous Definitions of Abrupt Climate Change, 23 Definition of Abrupt Climate Change for this Report, 26 Historical Perspective—Previous Reports on Abrupt Change, 29 This Report, 36 2 Abrupt Changes of Primary Concern 39 Abrupt Changes in the Ocean, 39 Abrupt Changes in the Atmosphere, 67 Abrupt Changes at High Latitudes, 81 Abrupt Changes in Ecosystems, 101 3 Areas of Concern for Humans from Abrupt Changes 127 Ecosystem Services, 127 Infrastructure, 136 Other Areas of Importance for Humans from Abrupt Changes, 143 4 The Way Forward 147 What Has Been Learned?, 147 Anticipating Surprises, 157 ACEWS: Need for Action, 168 References 171 Appendix 203 xiii

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