The Effects of Solar Variability
on Earth’s Climate

A Workshop Report

Committee on the Effects of Solar Variability on Earth’s Climate
Space Studies Board
Division on Engineering and Physical Sciences

NATIONAL RESEARCH COUNCIL
OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.

www.nap.edu



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The Effects of Solar Variability on Earth’s Climate A Workshop Report Committee on the Effects of Solar Variability on Earth’s Climate Space Studies Board Division on Engineering and Physical Sciences THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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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 is based on work supported by Contract NNH06CE15B between the National Academy of Sciences and the National Aeronautics and Space Administration and Grant No. AGS-1106426 between the National Academy of Sciences and the National Science Foundation. Any views or observations expressed in this publication are those of the authors and do not necessarily reflect the views of the agencies that provided support for the project. International Standard Book Number-13: 978-0-309-26564-5 International Standard Book Number-10: 0-309-26564-9 Copies of this report are available free of charge from: Space Studies Board National Research Council 500 Fifth Street, NW Washington, DC 20001 Additional copies of this report are available 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 2012 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 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. 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 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. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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Other Reports of the Space Studies Board Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar Systems Bodies (Space Studies Board [SSB], 2012) Assessment of a Plan for U.S. Participation in Euclid (Board on Physics and Astronomy [BPA] and SSB, 2012) Earth Science and Applications from Space: A Midterm Assessment of NASA’s Implementation of the Decadal Survey (SSB, 2012) Report of the Panel on Implementing Recommendations from the New Worlds, New Horizons Decadal Survey (BPA and SSB, 2012) Solar and Space Physics: A Science for a Technological Society [prepublication] (SSB and Aeronautics and Space Engineering Board [ASEB], 2012) Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation (SSB, 2012) Assessment of Impediments to Interagency Collaboration on Space and Earth Science Missions (SSB, 2011) Panel Reports⎯New Worlds, New Horizons in Astronomy and Astrophysics (BPA and SSB, 2011) Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era (SSB and ASEB, 2011) Sharing the Adventure with the Public⎯The Value and Excitement of “Grand Questions” of Space Science and Exploration: Summary of a Workshop (SSB, 2011) Vision and Voyages for Planetary Science in the Decade 2013-2022 (SSB, 2011) Capabilities for the Future: An Assessment of NASA Laboratories for Basic Research (Laboratory Assessments Board with SSB and ASEB, 2010) Controlling Cost Growth of NASA Earth and Space Science Missions (SSB, 2010) Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies: Final Report (SSB with ASEB, 2010) An Enabling Foundation for NASA’s Space and Earth Science Missions (SSB, 2010) Forging the Future of Space Science: The Next 50 Years (SSB, 2010) Life and Physical Sciences Research for a New Era of Space Exploration: An Interim Report (SSB with ASEB, 2010) New Worlds, New Horizons in Astronomy and Astrophysics (BPA and SSB, 2010) Revitalizing NASA’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce (SSB, 2010) America’s Future in Space: Aligning the Civil Space Program with National Needs (SSB with ASEB, 2009) Approaches to Future Space Cooperation and Competition in a Globalizing World: Summary of a Workshop (SSB with ASEB, 2009) Assessment of Planetary Protection Requirements for Mars Sample Return Missions (SSB, 2009) Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report (SSB with ASEB, 2009) A Performance Assessment of NASA’s Heliophysics Program (SSB, 2009) Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration (SSB with ASEB, 2009) Launching Science: Science Opportunities Provided by NASA’s Constellation System (SSB with ASEB, 2008) Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity (SSB, 2008) Limited copies of these reports are available free of charge from: Space Studies Board National Research Council The Keck Center of the National Academies 500 Fifth Street, NW, Washington, DC 20001 (202) 334-3477/ssb@nas.edu www.nationalacademies.org/ssb/ssb.html

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COMMITTEE ON THE EFFECTS OF SOLAR VARIABILITY ON EARTH’S CLIMATE GERALD R. NORTH, Texas A&M University, Chair DANIEL N. BAKER, University of Colorado, Boulder RAYMOND S. BRADLEY, University of Massachusetts PETER FOUKAL, Heliophysics, Inc. JOANNA D. HAIGH, Imperial College, London ISAAC M. HELD, National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory GERALD A. MEEHL, National Center for Atmospheric Research LARRY J. PAXTON, Johns Hopkins University PETER PILEWSKIE, University of Colorado, Boulder CAROLUS J. SCHRIJVER, Lockheed Martin Advanced Technology Center KA-KIT TUNG, University of Washington Staff ABIGAIL A. SHEFFER, Associate Program Officer, Study Director ARTHUR A. CHARO, Senior Program Officer CATHERINE A. GRUBER, Editor AMANDA R. THIBAULT, Research Associate TERRI M. BAKER, Senior Program Assistant (through April 6, 2012) DIONNA WILLIAMS, Program Associate DANIELLE PISKORZ, Lloyd V. Berkner Space Policy Intern MICHAEL BARTON, Lloyd V. Berkner Space Policy Intern MICHAEL H. MOLONEY, Director, Space Studies Board v

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SPACE STUDIES BOARD CHARLES F. KENNEL, Scripps Institution of Oceanography, University of California, San Diego, Chair JOHN KLINEBERG, Space Systems/Loral (retired), Vice Chair MARK R. ABBOTT, Oregon State University JAMES ANDERSON, Harvard University JAMES BAGIAN, University of Michigan YVONNE C. BRILL, Aerospace Consultant ELIZABETH R. CANTWELL, Lawrence Livermore National Laboratory ANDREW B. CHRISTENSEN, Dixie State College of Utah ALAN DRESSLER, The Observatories of the Carnegie Institution THOMAS R. GAVIN, California Institute of Technology HEIDI B. HAMMEL, AURA FIONA A. HARRISON, California Institute of Technology JOSEPH S. HEZIR, EOP Group, Inc. ANTHONY C. JANETOS, University of Maryland JOAN JOHNSON-FREESE, U.S. Naval War College ROBERT P. LIN, University of California, Berkeley MOLLY K. MACAULEY, Resources for the Future, Inc. JOHN F. MUSTARD, Brown University ROBERT T. PAPPALARDO, Jet Propulsion Laboratory, California Institute of Technology MARCIA J. RIEKE, University of Arizona DAVID N. SPERGEL, Princeton University MEENAKSHI WADHWA, Arizona State University CLIFFORD M. WILL, Washington University THOMAS H. ZURBUCHEN, University of Michigan MICHAEL H. MOLONEY, Director CARMELA J. CHAMBERLAIN, Administrative Coordinator TANJA PILZAK, Manager, Program Operations CELESTE A. NAYLOR, Information Management Associate CHRISTINA O. SHIPMAN, Financial Officer SANDRA WILSON, Financial Assistant vi

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Preface Experts on solar physics, solar variability, climate science, climate models, paleoclimatology, atmospheric science, and experts on other stars came together on September 8-9, 2011, at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, to discuss how the Sun’s variability over time has affected Earth’s climate. The National Research Council was asked by program managers at the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) to organize an interdisciplinary public workshop to examine the state of knowledge of Earth’s climate response to solar variability and to explore some of the outstanding science questions that might guide future research endeavors. As noted above, this particular topic touches upon a number of diverse research areas; a workshop such as this brings together scientists that do not always have an opportunity to interact as a group. A Committee on the Effects of Solar Variability on Earth’s Climate was formed and met on April 25, 2011, at the National Academies Keck Center in Washington, D.C., to develop an agenda for the workshop. Speakers were invited to submit abstracts, and these talks were organized into sessions by the committee. The workshop was advertised to the public through various media. During the workshop, the audience was encouraged to interact with the speakers and discuss the issues from different viewpoints. A final panel discussion was lead by chairs of the sessions, and the entire group was encouraged to share their thoughts on open research questions in these fields. A complete statement of task and workplan for the project can be found in Appendix A. The workshop featured presentations on a variety of topics related to solar variability and climate change, organized as follows: • The Sun and Solar Variability: Past and Present —Overview of solar and heliospheric variability —Observations of the Sun’s variable outputs —Techniques for revealing past solar changes • Sun-Climate Connections on Different Timescales —Evidence of solar influences in the troposphere and stratosphere —How the climate system works and how it might respond to solar influences —Indications of influence based on paleoclimate records • Mechanisms for Sun-Climate Connections —Mechanisms connecting variations in total solar irradiance directly to the troposphere —Mechanisms that influence upper parts of the atmosphere, such as variations in solar ultraviolet radiation and possibly solar energetic particles —Mechanisms that link variations in galactic cosmic rays to climate change. This workshop report contains no recommendations, findings, or statements of consensus. Instead, this workshop report summarizes the views expressed by individual workshop participants (invited speakers and guests). Also included is background information intended to provide context to the reader on both the solar and climate science topics presented at the workshop; however, this is not intended to be an exhaustive review of the current state of the science. Although the committee is responsible for the overall quality and accuracy of the report as a record of what transpired at the vii

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workshop, the views contained in the report are not necessarily those of all workshop participants, the committee, or the National Research Council. The committee thanks the NCAR Mesa Laboratory, in particular, Gerald Meehl, Stephanie Shearer, and Eron Brennan, for providing meeting space and excellent technical support. viii

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Acknowledgment of Reviewers 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 (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 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: Lennard Fisk, University of Michigan, Philip Judge, National Center for Atmospheric Research, Fabrizio Sassi, Naval Research Laboratory, and Nathan Schwadron, University of New Hampshire. Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse any of the viewpoints or observations detailed in this report, nor did they see the final draft of the report before its release. The review of this report was overseen by Joyce Penner, University of Michigan. Appointed by the NRC, she was 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. ix

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Contents OVERVIEW 1 1 BACKGROUND 3 The Potential Sun-Climate Connection, 3 The Measurement Record from Space, 4 Potential Perturbations of Climate Due to Solar Variability, 6 This Workshop Report, 8 2 WORKSHOP PRESENTATIONS 9 The Sun and Solar Variability—Past and Present, 9 Evidence of Sun-Climate Connections on Different Timescales, 18 Mechanisms for Sun-Climate Connections, 21 3 PANEL DISCUSSION 28 APPENDIXES A Statement of Task and Preliminary Workplan 33 B Workshop Agenda and Participants 34 C Abstracts Prepared by Workshop Speakers 38 D Biographies of Committee Members and Staff 51 E Acronyms and Terms 57 xi

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