David Archer - The Warming Papers: The Scientific Foundation for the Climate Change Forecast

This edition first published 2011 2011 by Blackwell Publishing Ltd

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Library of Congress Cataloging-in-Publication Data

The warming papers : the scientific foundation for the climate change forecast / edited by David Archer and Raymond Pierrehumbert.

p. cm.

Includes bibliographical references and index.

ISBN 978-1-4051-9616-1 (pbk.) ISBN 978-1-4051-9617-8 (hardcover)

1. Greenhouse effect, Atmospheric. 2. Greenhouse gases. 3. Global temperature changes. I. Archer, David, 1960

II. Pierrehumbert, Raymond T.

QC912.3.W37 2011

551.5dc22

2010040516

A catalogue record for this book is available from the British Library.

1 2011

Preface

Global warming is arguably the defining scientific issue of modern times, but it is not widely appreciated that the foundations of our understanding are almost two centuries old. The sensitivity of climate to changes in atmospheric CO2 was first estimated about one century ago, and the rise in atmospheric CO2 concentration was discovered half a century ago. The fundamentals of the science underlying the forecast for human-induced climate change were being published and debated long before it started to appear in the newspapers.

The aim of this book is to gather together the classic scientific papers that are the scientific foundation for the forecast of global warming and its consequences. These are not necessarily the latest in the state of play; there can be subsequent quantitative revision. But these papers are the big ideas. Some of the good old good ones can be heavy going, it must be admitted, so we will try to guide the reader with some verbage of our own, unworthy though it may be. We summarize the results for you, and provide the latest revisions from the ongoing literature, how strong the water vapor feedback turned out to be, for example. We will fill in the context, the personalities, and the aftermath of the ideas in the papers. Well also presume to provide short comments where they occur to us in boxes throughout the papers, signposts to help guide the casual reader.

Fourier, J. (1827). Mmoire sur les Tempratures du Globe Terrestre et des Espaces Plantaires. Mmoires de lAcadmie Royale des Sciences,7, 569604. 25 pages.

Joseph Fourier (17681830) is generally credited with the discovery of what is now known as the greenhouse effect. In fact, his contribution to the study of planetary temperature is even more profound than that. Fourier introduced the problem of planetary temperature as a proper object of study in physics, and established a largely correct physical framework for attacking the problem. His work set the stage for most of the further developments in this area over the remainder of the nineteenth century. Indeed, it was only toward the end of that century that physics had caught up to the point that the first quantitative estimates of the Earths temperature based on Fouriers concepts could be attempted.

If much of Fouriers reasoning in this paper seems qualitative, it should be recognized that most of the areas of physics that Fourier needs to call on were in their infancy in Fouriers day. Infrared radiation (called dark heat or dark radiation at the time) had been discovered in 1800 by the astronomer Sir Frederick William Herschel, and it was the subject of intense inquiry. Infrared was the dark energy of its day and it was perhaps no less mysterious to physicists of Fouriers day than is the dark energy talked about by todays physicists. There was some understanding from the work of Fouriers contemporaries, Dulong and Petit, that the rate of heat loss by infrared radiation increases with temperature, and it was known that infrared could carry heat through a near-vacuum. There was, however, only a limited ability to do quantitative calculations involving infrared heat transfer. Thermodynamics was in its infancy. The very nature of heat was still being hotly debated; the landmark energy conservation experiments of Joule that showed the equivalence of mechanical work and heat would not be carried out until 1843. Against this context, the general correctness of Fouriers great leap of intuition seems all the more remarkable.

In his 1827 paper, Fourier introduces five key concepts:

Fouriers inferences concerning the minimal influence of the Earths interior heat on climate are drawn from observations of the way temperature varies with depth below the Earths surface. Of all Fouriers claims in the 1827 paper, this is the one that is most backed up by quantitative reasoning, though the actual mathematical analysis appears in Fouriers other papers and is not reproduced in the 1827 essay. Fouriers greatest work as a mathematical physicist was the formulation of the partial differential equation describing the diffusion of heat within a body, and the development of the mathematical techniques required to solve it. The full range of these developments were engaged in Fouriers interpretation of the Earths subsurface temperature variations. Indeed, Fourier states that the problem of planetary temperatures provided the main impetus for his formulation of the analytical theory of heat. His theory of heat was applied to the problem in two basic ways. First, since the rate of heat flow is proportional to the temperature gradient, the measured increase of time-mean temperature with depth itself shows that the interior of the Earth is hotter than the surface, and gives an estimate of the heat flux, provided that one can estimate the thermal conductivity of the Earth. The flux Fourier arrived at using this procedure was an overestimate compared to modern calculations because he used the thermal conductivity of iron, but his calculation nonetheless showed the diffusion of heat from the interior to be an insignificant factor in surface temperature. The second kind of problem Fourier did was to impose the observed time-periodic daily and seasonal fluctuations of temperature at the surface as a boundary condition, and then calculate what the subsurface temperature fluctuations should look like. It was this kind of calculation that led Fourier to develop what we now call Fourier series, so as to decompose the complex time-periodic boundary condition into a sum of simple sines and cosines for which the problem is analytically tractable. This calculation correctly predicts that the diurnal variation of temperature should decay rapidly with depth and the annual variation more slowly. The calculation also gives an estimate of the amount of heat that flows into and out of the surface from sunlight in the course of the diurnal and seasonal cycle, and thus provides an additional check on the importance of solar energy in determining the Earths surface temperature.