Preface

The purpose of the second edition of this book is the same as the first, to provide an introductory guide to the development and use of three-dimensional computer models of the global climate system, including four major components: atmosphere, oceans, land/vegetation, and sea ice. Processes in each of these components, as well as interactions among them, are examined from the point of view of basic principles and in the context of recent developments. In dealing with each aspect we attempt to show how the theory grew historically from fundamental beginnings and how well it is able to account for known aspects of the climate system. For example, the current models describing the general circulation of the atmosphere evolved from early numerical weather prediction models, which in turn evolved from simple theoretical models. Today’s simulations and predictions are far better than those of a few decades ago and succeed in simulating major features of the atmosphere, oceans, land/vegetation, sea ice, interactive chemistry and Earth’s ecological systems. 
 
Most review articles that have dealt with the development of climate models have presumed of the reader a great deal of prerequisite knowledge of atmospheric or ocean dynamics. However, as widespread use of these models is growing in new areas of atmospheric sciences, geography, geology, hydrology, oceanography and ecology, there is a need to explain the models from a more elementary level. This book, in both its first and second editions, attempts to do that. 

The book is organized so that a reader initially only vaguely aware of climate models will be able to gain an understanding of what the models are attempting to simulate, how the models are constructed, what the models have succeeded in simulating, and how the models are being used for evaluative and predictive purposes. After a short introduction, provided in Chapter 1, Chapter 2 describes the climate system, largely from observational evidence. Chapters 3 and 4 are the two most theoretical chapters, describing the equations and numerics, respectively, behind global climate models, as well as the various approximations made, both physical and numerical. We provide addresses for several models available via the internet. Chapter 5 provides a few examples of how well the models have simulated various aspects of the climate system, including the basic global patterns of wind, temperature, precipitation, ocean currents, and sea ice distributions. In several cases, the chapter presents corresponding simulated and observational fields for easy comparison. Chapter 6 illustrates what the models have simulated for the response of the climate to various changes imposed on it, such as those due to changes in solar output or to increases in atmospheric carbon dioxide and other greenhouse gases. Many of the responses are predictable in a qualitative sense, but due to the multiple feedbacks in the climate system many are not, so that the numerical modeling approach provides a method of obtaining answers not obtainable by other means. Finally, since this is a rapidly evolving field, Chapter 7 provides some discussion of expected future developments. The book is supplemented by 12 appendices providing a variety of additional details and a list of internet links for climate modeling and climate data. 
 
Although it is assumed that the reader has some knowledge of calculus and introductory physics, the orientation of the book is pedagogical. It can be used within a graduate-level course on global climate modeling, as a supplement to advanced courses in atmospheric and ocean sciences, or as a self-study text. It is hoped that the book will prove in large part self-contained for the nonexpert who desires an introduction to the basic principles upon which three-dimensional computer models of the climate system are based. It can thereby serve as the basis for understanding more detailed discussions in scientific journals and advanced texts. We hope that the pedagogical approach will help scientists who have not been involved in climate modeling appreciate both the strengths and the weaknesses of the models and enable them to consider potential applications of the models for their own research.