The public is worried and so governments - at least the democratic ones - should also be worried. The global environment is changing and the consequences are still not understood. How much is natural and how much anthropogenic? In many cases the changes appear to be for the worse. Scientific opinion, as evidenced through the reports of the Intergovernmental Panel on Climate Change, is gloomy. By most estimates the rate of change will continue to increase and, if we cannot halt or slow the driving processes major modifications in where and how we live will be essential for survival. How do we know this and what should be done about it?