You'll think i'm exaggerating, but what happens between now and the end of 2009 could well determine the future of humankind. here's why: the evidence suggests that accelerating climate change is much, much worse than scientists believed possible even a few years ago. The only answer to this crisis is a radical decarbonisation of the global economy - not over the next 40 years, but over the next 20. We need a global agreement to make that happen, and it needs to be struck at the Copenhagen Climate Change Conference in November 2009. Anything else will be too late.

This would be a tough enough message to persuade world leaders to buy into at the best of economic times. By general agreement, 2009 will be the worst of economic times since the Great Depression in the 1930s. So the future of humankind could be said to hang on this paradox: the deepest recession in living memory will provide the best opportunity to finally get to grips with the challenge of climate change.

Ludicrously over the top? This isn't the place to rehash the science behind climate change in any great detail, but scientists all around the world now agree that the consensus laboriously negotiated by the Intergovernmental Panel on Climate Change (IPCC) in 2007 is already way out of date.

All the evidence that's come in since 2005 (the cut-off date for the IPCC's complex, peer-reviewed processes) confirms two things: that the impacts of climate change on the ground are already much more severe than anticipated, and that the pace of change is continuing to accelerate in ways that very few people predicted.

Let's look at just one example of this - the Arctic. On average, temperatures in the Arctic have increased by around 4º C over the past few decades. This has contributed hugely to the melting of the Arctic's summer sea ice, which reached its lowest level in 2007 - 40% below the summer average for 1979-2000. Many Arctic scientists are now predicting an ice-free summer in the Arctic by 2015 - more than 80 years ahead of the predictions of the IPCC 2007 report.

Albedo flip
A lack of ice will have huge consequences. Ice reflects up to 90% of incoming solar radiation away from the Earth (the so-called 'albedo effect'). Dark seawater absorbs between 80-90% of that radiation. This 'albedo flip' will cause increased warming across the entire region, which could reach as far as 1,500km inland. This will accelerate the melting of both the Greenland Ice Cap and the Arctic Permafrost, under which is trapped billions of tonnes of methane - a greenhouse gas more than 20 times as powerful as CO2. There is new evidence that methane trapped under the ocean floor along Russia's vast continental shelf is already bubbling up to the ocean's surface.