The Guardian reports on a major new study from the UK's Hadley Centre highlighting the need for urgent action to reduce greenhouse gas emissions. The Hadley Centre modelled various emissions reduction scenarios to see what their effects would be. Business as usual - doing nothing - would result in a rise in global mean temperatures of 5.5 - 7.1 C by the end of the century, a level which according to the IPCC [PDF] will cause mass extinction, famine, drought, and serious flooding (and which is likely to lead to "large-scale, high-impact, non-linear and potentially abrupt changes in physical and biological systems", like melting icecaps, clathrate releases, or the Amazon drying up and turning into a desert). Reducing emissions will reduce the impact, but we can only keep the global temperature within the "safe" range if we act swiftly and strongly. That means a 3% annual reduction in global emissions starting from 2010, with a target of a 50% reduction by 2050.
That's going to be a difficult target to meet, and an even more difficult target to get governments to agree to aim for. But if we don't meet it, then we're all screwed.