global warming

   Concerns about ‘global warming’ result from the observation that globally averaged temperatures have risen steadily by about 0.5°C over the last 100 years, and that some glaciers and the polar ice caps are retreating. Whether these data are conclusive remains contentious. It is proposed that global warming is caused by the increasing emissions of carbon dioxide and methane derived from the burning of fossil fuels by humankind. Sunlight absorbed by the earth warms it, but the average temperature is a result of the balance between heat absorbed and heat lost through the atmosphere. Carbon dioxide and methane reduce the loss of heat through the atmosphere, and so an increase in their concentration would be expected to give rise to an increase in average temperature (the greenhouse effect). An increase in temperature will decrease the amount of ice at the poles and thus lead to a rise in mean sea level. The possible extent of the rise predicted over the next century is sufficient to cause potential problems for low-lying cities like London and for whole countries like the Netherlands and Bangladesh.

   See also: Gaia hypothesis; nature

   PETE SHETERLINE