According to this report, acting now to avoid the negative consequences of global warming will require 1% of GDP, while waiting until later will cost between 5-20% of GDP:
Economist: Global warming will be costly, by Thomas Wagner, The Associated Press: A comprehensive report on the global economic cost of climate change, to be released by the British government Monday, is expected to be the world's most serious effort to quantify the long-term effect of doing nothing.
The Independent newspaper reported Friday that the long-awaited review would say global warming could cost the world's economies up to 20 percent of their gross domestic product if urgent action is not taken to stop floods, storms and natural catastrophes.
Author Sir Nicholas Stern met privately with Prime Minister Tony Blair and his Cabinet ministers Thursday to brief them about his findings. Stern, a government adviser on climate change, is a former chief economist of the World Bank.
Quoting unidentified officials at the briefing, The Independent said Stern warned the world would have to pay 1 percent of its annual gross domestic product now to avert catastrophe but that doing nothing could later cost five to 20 times that amount.
"Business as usual will derail growth," the paper quoted Stern as saying as he briefed the government on his 700-page report, covering a period up to the year 2100.
The report was mandated by Blair's treasury chief, Gordon Brown, who is expected to replace Blair when he steps down as prime minister next year. Brown recently said he would use the report to alert governments around the world that they have been too slow to recognize — let alone fight — the threat of climate change. ...