According to the Observer, the Stern report says unchecked climate change would cost up to US$6.98 trillion (A$9 trillion) - more than World Wars I and II and the Great Depression of the 1930s.
It also warns that the world needs to spend about one per cent of global gross domestic product - equivalent to about US$349 billion (A$454 billion) - on the issue now or face a bill up to 20 times higher than that in future, the paper says.
Stern also calls for a successor to the Kyoto agreement on greenhouse gases to be signed next year, not in 2010 or 2011 as planned, because the problem is so urgent, according to the paper.
He reportedly says that failure to act quickly would trigger a global recession and calls for an international framework to tackle the issue.
The Observer says his report is the first heavyweight contribution to the debate on climate change by an economist rather than a scientist.
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