Global warming is a term that entered the domain of both popular and scientific literature during the 1980s. It is closely linked with the idea of an increasing greenhouse effect, which was first calculated by a Swedish chemist, Svente August Arrhenius, in 1896 (Arrhenius 1997). It is believed that our atmosphere acts rather like a greenhouse, in which the glass allows solar radiation to pass through, where it is converted into heat. This heat is absorbed by the soil before being radiated out as long-wave radiation and intercepted this time by the glass, which re-radiates some of the energy back into the greenhouse. The atmosphere has properties rather similar to the glass of the greenhouse, hence the ‘greenhouse effect’, originally postulated by the French mathematician Jean-Baptiste Fourier (1824).
Global warming would seem to imply that the whole atmospheric system is warming up as a result of the greenhouse effect, but this is far from certain. Once the nature of the problem has been outlined, three main areas of investigation will be addressed. First, there is the scientific evidence for global warming; second, the study of the likely impacts and third, the formulation and implementation of strategies to cope with such impacts. The contribution of geographers has chiefly been in the applied field of impact studies.
The ‘natural’ greenhouse effect occurs because some of the gases present in the atmosphere are largely transparent to incoming solar radiation but not to outgoing radiation, which is partially absorbed by water vapour, and the three main greenhouse gases. Their current percentage contributions are 70 per cent for carbon dioxide, 23 per cent for methane and 7 per cent for nitrous oxide. Water vapour is very variable in time and space. CFCs (chlorofluorocarbons) and their interaction with the variable greenhouse gas, ozone, also need to be noted as potential contributors (IPCC 1990). These gases are collectively known as ‘the greenhouse gases’. The additional amount of such gases that are present in the atmosphere as a direct or indirect result of human activity, such as power generation and vehicle emissions, leads to an ‘enhanced’ greenhouse effect.
Although carbon dioxide is not the strongest absorber of outgoing long-wave terrestrial radiation, it is believed that it has the greatest long-term potential for raising global temperatures. Most attention has therefore been directed to the increase in the concentration of carbon dioxide from 280 ppmv (parts per million by volume) at the beginning of the Industrial Revolution in the eighteenth century to current levels of 360 ppmv (Figure 2.1). The annual increase of about 1.8 ppmv adds 3.8 Gt (gigatonnes) to the atmospheric carbon reservoir of