The earth’s atmosphere is now changing more quickly than at any time in the past. In the last 150 years there has been a 25 percent increase in the carbon dioxide and a 100 percent increase in methane in the atmosphere, largely as a result of the burning of fossil fuels’ the expansion of agriculture and rapid deforestation. Over the same period, the world has warmed by an average of 0.5. C, as green house gases trap the Suns heat within the atmosphere. Computer models predict a continued warming of 0.2. C a decade unless steps are taken to limit emissions. The warming would be greater were it not for pollutants such as sulphur dioxide which scatter sunlight back onto space. Other gases- notably CFCs are damaging the tenuous layer of ozone in the stratosphere which screens out ultraviolet radiation from the sun. Steps have been taken to phase out CFCs. Legislation to reduce other green house gases will be harder to implement since the practices that produce them are central to modern life. Many nations have pledged to reduce emissions to their 1990 levels, but stronger measures will be needed if global warming is to be averted.