Atmosphere, Clouds, and Climate

David Randall (Princeton University Press, 2012), 277 pp, $27.95, ISBN 978-0-691-14375-0 (paper); ISBN 978-0-691-14374-3 (hardcover)

This book is a volume in the series “Princeton Primers in Climate.” Author David Randall, a professor of atmospheric science at Colorado State University, describes his goals in the preface: “to teach you something about the role of atmospheric processes in climate and to entice you to want to know more.” The book is aimed at “college undergraduates who have an interest in climate and some familiarity with basic physics.” Randall assumes familiarity with basic calculus and there are a few equations in almost every chapter, “but there are no complicated derivations. The penalty paid for this simplicity is that the explanations given are much less complete and rigorous than they could be in a more technical book.”

The book’s nine chapters are: (1) Basics; (2) Radiative Energy Flows; (3) How Turbulence and Cumulus Clouds Carry Energy Upward; (4) How Energy Travels from the Tropics to the Poles; (5) Feedbacks; (6) The Water Planet; (7) Predictability of Weather and Climate; (8) Air, Sea, Land; (9) Frontiers.

The author uses a section heading every few pages to divide each chapter into recognizable and easily searchable sections. For example, the nine sections of Chapter 3 are titled Energy Flows Back to the Atmosphere; Turbulent Mixing; Stratification; Static Stability and Instability in Dry Air; Cumulus Instability; Widely Spaced Towers; What Determines the Intensity of the Convection?; Cumulus Fluxes of Energy and Other Things; and Appendix to Chapter 3: More About Energy Fluxes. Randall also usually closes the narrative of each chapter with a look ahead at what is coming next.

The reading aids are needed, because the author’s treatment is faithful to the complexity and subtleties of his topic: calculus (including partial derivatives) and vector algebra (specifically vector cross products in treating the geostrophic wind) are used when necessary. The text includes nearly 70 equations, but it also includes more than 40 tables and figures, most of which are discussed well in captions and the narrative, and there is also a good glossary of nearly 60 terms.

Although the subject requires serious attention to technical detail, the author is willing to be informal to be clear. For example, on pp. 90-91, Randall concludes his treatment of “convective available potential energy” (CAPE) with these two paragraphs:

“To gain an intuitive understanding of why this is true, consider an earthy analogy. In this analogy, the convection is represented by a large, very hungry dog. The CAPE is the food in the dog’s bowl. CAPE is generated when you, the dog’s human companion, add food to the bowl. The ravenous dog wolfs the food down as fast as it appears, so the rate at which the dog consumes the food (the intensity of the convection) is equal to the rate at which you supply the food (the rate of CAPE production).

“Because the dog is such an efficient eater, the bowl is always nearly empty. The analogy here is that the convection consumes CAPE so efficiently that the measured CAPE is always close to zero, despite the fact that CAPE is continually generated by various processes. Because of this, the actual lapse rate is observed to be close to the moist adiabatic lapse rate (Xu and Emanuel, 1989) throughout the tropical troposphere (except in the boundary layer). For reasons explained in Chapter 4, this is true even in portions of the tropics that are far away from regions of active convection.”

This excerpt also shows the author’s commendable readiness to vary his degree of formality to suit the pedagogical purpose. Notice also the citation of an article in the professional literature. There are more than 70 such works in the bibliography, as well chapter-by-chapter suggestions for further reading. These cover a very wide range, from Arrhenius’ 1896 article on the influence of atmospheric carbon dioxide on Earth’s surface temperature through recent articles and monographs on climate science.

This reviewer detected a few flaws in the presentation. On page 34, Randall points out that the several important greenhouse molecules all have three or more atoms, and states that “molecules with only two atoms, such as molecular nitrogen and oxygen, do not absorb or emit infrared radiation.” This is true in practical terms, but not literally – diatomic oxygen does absorb in several narrow bands in the infrared. In Chapter 2, the text might have been clearer about the fact that different sign conventions are used in Table 2.1 and Figure 2.5. In Chapter 3, Randall uses two different terms (“water vapor mixing ratio” and “specific humidity”) for the same quantity without being explicit about it.

Such minor matters do not significantly detract from what is an excellent presentation of a complex subject. Each chapter explains well what it claims to tackle. One of the strongest chapters is Chapter 7: Predictablity of Weather and Climate. Here are two paragraphs from pp. 202-203:

“If weather prediction is impossible beyond two weeks, how can climate prediction be contemplated at all? Two factors have the potential to make climate change prediction possible. First, the climate system has components with very long memories, including especially the ocean. Second, the climate system responds in systematic and predictable ways to changes in the external forcing.”

“Weather prediction is very different from climate prediction because changes in the day-to-day weather are not due to changes in the external forcing, while changes in climate are. Weather prediction is limited by sensitive dependence on past history. Climate prediction is not.”

The admonition that “There is no royal road to Geometry” is attributed to Euclid, and the same can certainly be said about atmospheric science. The path to expert knowledge is arduous. But for the reader who is prepared to think carefully and sometimes mathematically, David Randall’s primer is a wonderful companion for starting along that path. I recommend it highly.

William H. Ingham, Professor Emeritus
James Madison University
inghamwh@jmu.edu

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.