The hole story

I judge a popular book on weather and climate on whether I can read it from cover to cover in one sitting, with pleasure, and without being irritated by errors of fact, lack of balance in content and argument, sloppy expression, or condescending facetiousness. Very few books satisfy all these criteria, often because the authors have no clear idea of their aim and target. In The Forgiving Air, Richard Somerville has a definite mission to sensitise the intelligent and concerned layman to some of the most important environmental issues, notably global warming, depletion of stratospheric ozone, and acid rain, to explain in simple terms the underlying scientific processes and their social and economic impact. As one would expect from a distinguished professor of meteorology, the underlying science is accurately and clearly presented but the structure and style are less satisfactory. In a book of this kind it matters not only what you say but how you say it.

The first chapter gives a straightforward account of the meteorology and chemistry involved in the depletion of stratospheric ozone, most severely over the Antarctic continent in October-November and, to a lesser extent, over the Arctic in April-May. The story is made more interesting by recalling big historical events such as Thomas Midgley's discovery in 1928 of chlorofluorocarbons (CFCs) as safe refrigerants; Joe Farmer's 1981 discovery of the "ozone hole" from measurements made at Halley Bay but missed by United States scientists who had programmed their computer to reject "other" observations as rogues; and the proposal in 1974 by Mario Molina and Sherwood Rowland that the ozone was destroyed by the catalytic action of chlorine released by the photolytic breakdown of CFCs.

But Somerville gives little idea about the great complexity of the many chemical reactions involved, especially those thought to take place on the surface of ice crystals formed in very high cold stratospheric clouds in the polar night. He is also rather reticent about the fact that computer models containing more than 100 chemical reactions do not yet provide satisfactory quantitative explanations for the rapid formation of the ozone hole and its subsequent recovery in the summer.

A chapter describes the basic physics of the natural greenhouse effect, how the earth's temperature is governed by the radiative properties of carbon dioxide, water vapour and the lesser greenhouse gases, and how their concentrations have increased since the industrial revolution. In describing how man-made emissions of these gases may enhance the natural greenhouse effect and lead to global warming and other changes in climate, the author does well to point out that the problem is different in nature and more difficult to remedy than ozone depletion.

The longest chapter deals with computing of weather and climate. It offers some valuable insights into the nature, complexity and deficiencies of computer models of climate change, in particular the role of the many feedback processes that complicate the understanding and predictability of the system, but it is often too discursive, digressive, and repetitive to maintain the thread and is marred by some silly and unconvincing analogies. Strangely, there is no indication of the magnitude of the computing task; that running an advanced global model for just one annual cycle involves more than 100 trillion numerical operations.

In discussing possible responses and actions to limit global change, Somerville points out that since it is difficult to distinguish possible human-induced change from natural climatic fluctuations, and because model predictions have markedly changed in recent years as the moderating effects of the oceans and clouds have become more apparent, scenarios about the future social and economic impacts of climate change are mostly speculative and hypothetical. He calls for more research to provide a firmer scientific base for political action and sensibly argues that some of the proposed schemes to remove carbon dioxide from the atmosphere, for example, by large-scale planting of trees or putting iron into oceans to promote growth of plankton, are misconceived and impractical.

He does well to emphasise that increasing emissions of carbon dioxide, like many other environmental problems, will result mainly from large increases in population and industrialisation in developing countries such as India and China, which will continue to increase coal production so that realistic reductions in emissions by the developed world will have little overall effect on global warming. But he proceeds to argue, illogically, for a major switch from fossil fuels to renewable sources of energy - tidal, solar, geochemical, wind and hydropower (but not nuclear!) - for which developing countries would not have the necessary financial and technological resources.

It seems we shall have to adjust to a world warmer on average by perhaps 1-3 degrees Celsius by the end of next century, but with larger changes in some regions than others. Rich countries with diverse agriculture and industry, adequate water resources, and a strong scientific and technological base will cope. Much of the third world, with rapidly increasing population, may find climate change an additional, but by no means the greatest burden to bear.

The author appears to have taken too much advice on making the text "user-friendly". Some well-chosen diagrams (there is only one), would have been helpful. The many matey injunctions, asides, and expressions, such as "the measurements have been dirtied up'', do little to enlighten the argument but will irritate many readers. This approach leads to inconsistency in the level of presentation. The reader, having been treated to a fairly complex scientific argument, hardly needs to be reminded that a millimetre is "about the thickness of the wire used in a paper clip; an inch is about 25 millimetres''; or receive a mini-lecture on the meaning of powers of ten.

At Pounds 17.95 for 195 pages of unillustrated text, it is rather expensive but, on the whole, this is a better book than most of its competitors.

Sir John Mason is senior advisor to the centre for environmental technology, Imperial College, London, and has recently retired as chancellor, UMIST.