Empirical Evidence for the Effect of Tropical Deforestation on Climatic Change

If large areas of tropical rain-forest are replaced by grassland, there is likely to be about 300 mm less evapo-transpiration and 650–800 mm less rainfall during each year in these areas than is currently experienced. Lower rates of evapotranspiration will allow more energy to be used for sensible heat, and this will lead to surface air temperatures that are higher than currently by about 3°C. Reduced cloud-cover will also lead to even higher temperatures, because clouds have a net cooling effect. When this additional heat is combined with the extrasensible heating, the overall effect is expected to be a rise in temperature of about 4–5°C.These contentions are based upon data obtained from ‘natural experiments’. They have given results which suggest that tropical deforestation will have a larger effect on temperature than was hitherto expected, and that the effect on both temperature and rainfall will be more widespread than has been expected hitherto. The effects on global climate cannot as yet be determined by a ‘natural experiment’.The removal of so much of the tropical rain-forest as is now projected will have such a dramatic effect on local and even wider climate that no further replacement of the rain-forest ecocomplex by others or other land-uses should be allowed to take place.