Deforestation is an environmental problem that threatens the survival of the entire current biosphere. It is counted among the most important environmental crises facing our planet, not least because of its role in reducing biodiversity, increasing global warming and expanding deserts. However, most humans live in degraded forest landscapes, agricultural and urban landscapes. These landscapes, like those of most long-settled areas, both within and outside the tropics, have been claimed from forest. They demonstrate that when the trauma of forest conversion is past, many—but not all—former forest lands may be managed sustainably and productively. Forest conversion is not, inherently, a bad thing for human society or even for the biosphere. Excessive forest conversion is another matter.
The world’s forests, especially the tropical forest belt, have been conceived as part of the planet’s cooling system (Lovelock 1990). Although less significant than the oceans, (estuaries and) tropical forests are key regulators. The forests remove atmospheric carbon dioxide and transform it into wood, soil, perhaps eventually peat, coal, etc. Forests also pump water into the atmosphere. The moisture produced creates clouds, which cool both the forests and the planet by reflecting solar radiation. The rain from these clouds helps to sustain more forest in areas that would otherwise be too dry (Dickinson 1987).
Deforestation may deprive the Earth of 2.5 Mg×109 (Gigatonnes) of above-ground biomass each year (World Resources Institute 1994). In the 1980s, tropical deforestation was thought to add 4.6 Mg×109 of carbon dioxide to the atmosphere, equivalent to more than 90 per cent of US emissions from energy and cement production and perhaps 20 per cent (±10 per cent) of global emissions from fossil fuel (ibid.). Fearnside (1997), argues that although 90 per cent of the planets forest biomass remains, continued losses of forest and cerrado savannah could dump 275 Mg×106 of carbon dioxide into the atmosphere through the next century. Deforestation is also reducing the planet’s ability to cool itself by removing carbon dioxide from the atmosphere. Using satellite data, Jang et al. (1996) estimate the impact of deforestation on the decline of global net primary productivity (NPP). Between 1986 and 1993, approximately 19 per cent (2,600,000 km2) of the high-NPP regions (>2000 g m−2 yr−1), mainly tropical rain forests, were reduced to intermediate-NPP regions (500-1500 g m−2 yr−1) mainly savannah and cultivated land (Jang et al 1996).
Lovelock (1991) warns that the loss of the tropical forests could contribute to a sudden and dramatic failure of the planet’s current system of climatic regulation, regarded as already being close to the margins of its stability. Using analyses based on the mathematics of dynamic systems theory, and images from the liveliest traditions of environmentalism, Lovelock predicts a future of