Climate change is likely to be a principal driver not only because it will be destructive, but also for a reason not always given due prominence – its potential to severely reduce world food supplies, especially in poor and heavily populated areas. Food, water and energy resources are now at the stage where, by 2030, even quite small changes in climate could cause major famine. Global warming is the most likely early prospect, predicted to increase progressively over the next 30 years. There is now almost complete consensus among scientists that it will happen, and that human activities that increase the amount of greenhouse gases in the air are the trigger.