The Role of the Sun in Climate Change Douglas V. Hoyt Kenneth H. Schatten Oxford University Press The ROLE of the SUN in CLIMATE CHANGE THE SUN ON JULY 6, 1979. FROM W. J. LIVINGSTON. The ROLE of the SUN in CLIMATE CHANGE Douglas V Hoyt Kenneth H. Schatten New York Oxford • Oxford University Press 1997 Oxford University Press Oxford New York Athens Auckland Bangkok Bogota Bombay Buenos Aires Calcutta Cape Town Dar es Salaam Delhi Florence Hong Kong Istanbul Karachi Kuala Lumpur Madras Madrid Melbourne Mexico City Nairobi Paris Singapore Taipei Tokyo Toronto and associated companies in Berlin Ibadan Copyright © 1997 by Oxford University Press, Inc. Published by Oxford University Press, Inc., 198 Madison Avenue, New York, New York 10016 Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Hoyt, Douglas V. The role of the sun in climate change / Douglas V. Hoyt, Kenneth H. Schalten. p. cm. Includes bibliographical references and index. 1SBN 0-19-509413-1; ISBN 0-19-509414-X (pbk.) 1. Solar activity. 2. Climatic changes. I. Schatten, Kenneth H. II. Title. QC883.2.S6H69 1997 551.6—dc20 96-10848 987654321 Printed in the United States of America on acid-free paper Acknowledgments We would like to thank Tom Bryant, Richard A. Goldberg, and O. R. White for reviewing a draft of this book. Their comments helped improve the book. Dr. Elena Gavryuseva and Dr. Ron Gilliland sent us the neutrino-flux calculations. Dr. Eugene Parker gave us an estimate of the energy-storage requirements in the solar convection zone associated with long-term changes in solar luminos- ity. Ruth Freitag of the Library of Congress aided in tracking down some bio- graphical information. Any errors are solely the responsibility of the authors, and any views expressed here do not reflect any organizational viewpoints. Finally, one reviewer of this book, who wishes to remain anonymous, receives our heartfelt thanks for greatly improving the readability of the text. This book is dedicated to all the pioneers of sun/climate studies. This page intentionally left blank Contents 1. Introduction 3 I. THE SUN 2. Observations of the Sun 9 3. Variations in Solar Brightness 48 II. THE CLIMATE 4. Climate Measurement and Modeling 83 5. Temperature 105 6. Rainfall 125 7. Storms 143 8. Biota 153 9. Cyclomania 165 III. THE LONGER TERM SUN/CLIMATE CONNECTION 10. Solar and Climate Changes 173 11. Alternative Climate-Change Theories 203 viii CONTENTS 12. Gaia or Athena? The Early Faint-Sun Paradox 216 13. Final Thoughts 222 IV. APPENDICES 1. Glossaries 229 2. Solar and Terrestrial Data 235 3. A Technical Discussion of Some Statistical Techniques used in Sun/Climate Studies 240 Bibliography 245 Index 275 The ROLE of the SUN in CLIMATE CHANGE This page intentionally left blank 1. Introduction About 400 years before the birth of Christ, near Mt. Lyscabettus in ancient Greece, the pale orb of the sun rose through the mists. According to habit, Meton recorded the sun's location on the horizon. In this era when much re- mained to be discovered, Meton hoped to find predictable changes in the loca- tions of sunrise and moonrise. Although rainy weather had limited his recent observations, this foggy morning he discerned specks on the face of the sun, the culmination of many such blemishes in recent years. On a hunch, Meton began examining his more than 20 years of solar records. These seemed to confirm his belief: when the sun has spots, the weather tends to be wetter and rainier. Theophrastus reported these findings in the fourth century B.C. Other an- cient accounts concerning the sun and weather are vague. If one stretches one's imagination, some comments by Aratus of Soli, Virgil, and Pliny the Elder may touch on this subject. What happened to the original records used by Theophrastus? Perhaps these and related scientific data were burned in the fire that destroyed the Library at Alexandria around A.D. 300. Other possible ancient accounts have vanished. Two thousand years passed. The Roman Empire rose and fell, the Dark Ages lasted a thousand years, and Europe entered the Renaissance. The 1600s reveal perhaps half a dozen scattered references to changes in the sun and their effect on weather. After a few more references in the 1700s, scientific interest in the sun waned. Following Sir William Herschel's comments on sunspots and climate in 1796 and 1801, about 10 scientific papers touched on the sun's in- fluence on climate and weather. The next two decades contain about 10 or so references to this topic. Shortly after a paper by C. Piazzi Smyth appeared in the proceedings of the Royal Society in 1870, the field exploded. This paper stimulated scientists such as Sir Norman Lockyer, Ferguson, Meldrum, and oth- ers to think about solar and terrestrial changes. Meldrum, a British meteorolo- 3 4 INTRODUCTION FIGURE 1.1 Indian Ocean cyclones and group sunspot numbers. One of the first pub- lished claims concerning a relationship between solar activity and terrestrial weather, Dr. Meldrum's data for the number of Indian cyclones from 1847 to 1873 are plotted versus sunspot numbers. This striking relationship inspired many follow-up studies, as well as the first wave of sun/climate investigations (see Chapter 7). (Data for original figure comes from Meldrum 1872, 1885.) gist in India, considered Indian cyclones. His tabular values are compared with sunspot numbers in Figure 1.1. The obvious and striking parallelism between the two curves convinced many scientists of the reality of the sun/climate relationship, and investigations began in earnest. Over the next two decades, dozens of papers appeared relating changes in the sun to variations in the Earth's temperature, rainfall and droughts, river flow, cyclones, insect populations, shipwrecks, economic activ- ity, wheat prices, wine vintages, and many other topics. Although many inde- pendent studies reached similar conclusions, some produced diametrically op- posed results. Certain studies were criticized as careless. Questions critics asked included: Why were people getting different answers at different locations? Why did some relationships exist for an interval and then disappear? Were all these results mere coincidences? Often, "persistence" and "periodicities" in two parallel time series can create the appearance of a coincidental relationship. These statistical problems are covered in chapter 5. To complicate the issue further, some scientists believed that the sun's vari- ations could explain everything about weather and climate. Other critics coun- tered that the reverse was true, and by the late 1890s the initial enthusiasm concerning the sun and its potential effects on the weather had waned to such an extent that few publications can be found. The critics appeared victorious, and the field nearly died. After this brief hiatus, a steady increase in the number of sun/climate studies has appeared in the twentieth century. Unfortunately, none of these new studies is definitive in either proving or disproving the sun/ climate connection. INTRODUCTION 5 Before writing this book, we compiled a bibliography of nearly 2,000 pa- pers and books concerning the sun's influence on weather and climate. Figure 1.2 shows the number of publications per year. Although incomplete (no doubt some technical reports and popular accounts were either missed or purposely omitted), our bibliography may be the most comprehensive assemblage of sig- nificant papers to date. To our knowledge, thus far no one has read all 20,000- plus pages of text in at least a dozen languages. Furthermore, many papers demonstrate poor statistical analyses, are too enthusiastic in their conclusions, or are repetitive. Critics today might even categorize these papers as fringe science and suggest they be ignored. Indeed, they might characterize the whole field as "pathological science." Whether this harsh judgment is justified remains to be seen. Although many scientists have arrived at the same conclusions while remaining entirely unaware of their colleagues' work, many reported effects are associated with incorrect or inadequate statistics. Rather than being a repository of absolute truths, the scientific literature remains an ongoing debate and dis- cussion. Some erroneous conclusions are always published; however, such er- rors should not invalidate an entire field of study. Rather than reviewing innumerable papers, we approach sun/climate change as one might an ongoing journey, highlighting only the better studies and those intriguing results we consider scientifically interesting. Our book is divided into three parts. 1. We start with an examination of solar ctivity and travel through history to reveal the slow development of our understanding of the sun. Observational accounts will be followed by a description of present-day solar theories. We will then examine why the sun varies and place the sun's variation within the context of other stars. FIGURE 1.2 The approximate number of sun/weather/climate publications each year from 1850 to 1992 arc shown (1,908 total). Note the initial surge of publications after 1870 followed by a decline around 1900. Since then, the increase in publications has remained almost steady. Two thousand papers represent less than 0.25% of the scien- tific literature published each year, so the sun/climate field remains relatively small. 6 INTRODUCTION 2. The central portion of this volume considers climate and the sun/climate connection, particularly on the 11-year time scale. We define what climate is and how sensitive climate would be to changes in the sun's radiative output.