Provoke the beast and create a very nasty atmosphere

Over the past half-century there has been an amazing change in attitudes towards the behaviour of that wisp of atmosphere round the earth we call climate. Of course, some people were always aware that climate changed, but the process was thought to be so slow that it could be scarcely be identified within a human lifetime. Indeed, the distinction between climate and weather was elusive. For many, God had created a world in which humans could flourish more or less in a perpetual present.

In this well-written book, Spencer Weart shows why and how attitudes changed to the point where, as our prime minister said last year, climate change became "unquestionably the most urgent environmental challenge".

In the 19th century, scientists such as Tyndall, Croll, Arrhenius and Maunder identified some of the mechanisms of climate, in particular the role of positive and negative feedback, the effects of carbon dioxide and other gases in retaining the earth's heat, and the possible influence of sunspots on climate. At the time their interpretations were questioned, and their work was mostly ignored.

Attitudes began to change in the 1920s and 1930s. Here, the work of Milankovitch was crucial. He correlated the successive Pleistocene ice ages with the changing relationship between the sun and the earth (its so-called wobble, tilt and spin). Evidence accumulated from many other sources, including greatly improved meteorological observations.

It became clear that human activities, in particular the emission of industrial materials into the atmosphere, could be affecting global climate and adding to the greenhouse effect. Another disturbing discovery was that climate could change within decades, not centuries.

The story is one of scientific pioneers - sometimes in passionate disagreement with each other, and often not knowing what others were doing - and Weart tells it well. Understanding climate involved astrophysicists, geochemists, geographers, biologists, meteorologists, statisticians, historians and even the military establishment (which was interested in the idea of manipulating weather to disadvantage an enemy). Mistakes had fruitful results in stimulating research to correct them and in driving new and better integrated methodologies. During the 1960s, awareness of environmental problems greatly increased, and by the time of the United Nations Conference on the Human Environment at Stockholm in 1972, climate change was firmly on the international scientific agenda.

But it had yet to make the transition into politics and policy-making. The uncertainties (was the earth getting warmer or cooler?) made the whole subject a quagmire. By the time of the first World Climate Conference in 1979 advice had become more reliable and more consistent. There is now a model institution of political and scientific cooperation in the form of the Intergovernmental Panel on Climate Change, and even an international treaty, the Framework Convention on Climate Change, with its implementing Kyoto Protocol.

Meanwhile, the volume of greenhouse gases in the atmosphere has risen to its highest for more than 400,000 years, and average global surface temperature has sharply increased, particularly in the past decade, most of it due to human activity. According to broad scientific consensus, it will go still higher (somewhere between 1.5C and 5.8C between 1990 and 2100). If the increase were to go anywhere near the higher figure, life on earth in all its aspects would undergo radical change.

There are still many unknowns. The relationship between climate and other environmental problems is equally uncertain: for example, the effects of human population increase, land degradation and destruction of biodiversity.

Measures to cope with them are highly contentious and outside the scope of this book. Some action is beginning, but nowhere yet on a scale that could have much effect.

Weart has done us all a service by bringing the discovery of global warming into a short, compendious and persuasive book for a general readership. He is especially strong on the early days and the scientific background.

The second half of the book, mostly on the politics, is somewhat selective and US oriented, with some omissions, and the chronology is sometimes muddled. But the lessons are loud and clear.

As Wallace Broecker once said, climate is a capricious beast, and we are poking it with a sharp stick. It is about time we stopped doing so.

Sir Crispin Tickell is chancellor, University of Kent, and the author of Climatic Change and World Affairs .