Climate And The Oceans

Geoffrey K. Vallis

PRINCETON UNIVERSITY PRESS Princeton & Oxford

Copyright © 2012 by Princeton University Press

Published by Princeton University Press 41 William Street, Princeton, New Jersey 08540 In the United Kingdom: Princeton University Press 6 Oxford Street, Woodstock, Oxfordshire 0X20 1TW press.princeton.edu

All Rights Reserved ISBN: 978-0-691-14467-2 (cloth) ISBN: 978-0-691-15028-4 (pbk)

Library of Congress Cataloging-in-Publication Data

Vallis, Geoffrey K. Climate and the oceans / Geoffrey K. Vallis. p. cm. — (Princeton primers in climate) Includes bibliographical references and index. 1. Oceanography—Research. 2. Ocean circulation. 3. Ocean-atmosphere interaction. 4. Climatic changes.

I. Title. GC57.V26 2011 551.5'246—dc22 2011014372

British Library Cataloging-in-Publication Data is available

This book has been composed in Minion Pro Printed on acid-free paper. ~ Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

Contents

Preface vii

1 Basics of climate 1

2 The oceans: A Descriptive overview 22

3 A Brief Introduction to Dynamics 41

4 The ocean circulation 75

5 The ocean's overall Role in climate 105

6 climate Variability from Weeks to Years 128

7 Global Warming and the ocean 156

Notes 205

Further Reading 211

Glossary 215

References 223

Index 229

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Preface

The truth and nothing but the truth, but not the whole truth.

This is a book on climate, with an emphasis on the role of the ocean. The emphasis is on large-scale processes and phenomena, and on the physical aspects of the ocean rather than its chemical or biological properties. It is not a textbook on physical oceanography, of which there are several good ones, nor is it a textbook on climate, of which there are some good ones. Rather, and as its size may indicate, the book is an introduction to, or a primer on, the ocean-climate system.

This book could be used to provide an introductory "big picture" for more advanced students or for scientists in other fields, or it could provide advanced reading for undergraduate students taking courses at a more elementary level. The book is somewhat more mechanistic than most books at this level: the emphasis is on how things work, and in particular how the ocean works and how it influences climate. I discuss observations to motivate the discussion, but the main emphasis is not on what things happen to be, but why and how they happen to be.

This is a fast book, although it is not, I hope, a loose book. It covers a lot of ground, quickly, and tries not to get bogged down in too much detail. Having said that, one of the most important questions to answer in the study of climate is to understand just what is a detail and what is essential. If one is studying the climate as a whole, then one might regard the presence of a small island in the northeast Atlantic as a detail, and it surely is (unless one is studying the climate of that island). One might also regard the precise way in which carbon dioxide molecules vibrate and rotate when electromagnetic radiation impinges upon them as a detail, yet it is precisely this motion that gives us the greenhouse effect, which makes our planet habitable, and which also gives us global warming, and which may affect our economy to the tune of trillions of dollars. Hardly a detail! But can we, and need we, understand all such matters to understand climate? Without answering that question, it is clear that in a short book such as this, choices have to be made. I will occasionally, but only occasionally, simply tell you how things are, without delving into the mechanisms if they are tangential to our narrative.

Given that we do move around sharp bends quite quickly, a certain amount of sophistication is assumed of the reader, or at least a willingness to think a little and puzzle things out and perhaps even look up one or two references. On the other hand, I haven't assumed much background knowledge—just a bit of basic physics and mathematics and some general knowledge about the ocean and climate. In other words, I'm writing the book for a smart and motivated but somewhat ignorant reader, and I hope you don't mind being so characterized. In some contrast to most elementary or undergraduate books, I have not shied away from topics that are of current interest or subjects of current research. It should be clear from both the text and the context when the contents of a section are not completely settled or are still a topic of research, rather than being wholly standard textbook material. I have tried to be as objective as possible when discussing such matters, but this attempt does not mean giving two sides of a controversial matter equal weight or suggesting that both are equally valid. Sometimes, an opinion is just plain wrong. The topics of current interest are especially noticeable in the second half of the book, in the chapters and sections on climate variability, global warming, and climate change. The chapter on ocean circulation also reflects our relatively recent understanding of the ocean's meridional overturning circulation. The more mathematical aspects of the book tend to be concentrated in the first half of the book, and the reader who may be surprised that some of the topics dealing with current research are less mathematical should ponder the quotation at the opening of chapter 3. Some readers may wish to skip ahead directly to chapters that particularly interest them, and this way of reading should be possible by referring back to the earlier chapters as needed.

I thank Peter Gent and Carl Wunsch for their perceptive reviews of an early draft of this book. They saved me from myself in a number of ways. Thanks also to

Ryan Rykaczewski, Stephanie Downes, Mehmet Ilicak, Rym Msadek, Caroline Müller, Amanda O'Rourke, Ilissa Ocko, Thomas Spengler, and Antoine Venaille, for many comments and constructive criticisms, even if they did it for the beer. The chapter on ocean circulation owes much to a couple of vigorous conversations with Max Nikurashin. Finally, my thanks to Cathy Raphael for expertly creating many of the figures.

CLIMATE AND THE OCEANS

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