Failure by governments to take bold action against global warming in the next decade could cost the world up to 6.98 trillion dollars, a report warns.
Excerpts of a 700-page report to be released on Monday by Sir Nicholas Stern, a former World Bank chief economist, also show that rampant climate change could turn 200 million people into refugees amid drought or flood.
The Observer weekly, which published the excerpts of a report it says is the first heavyweight contribution of an economist rather than a scientist on the phenomenon, also said failure to act would trigger a global recession.
"This will give us an argument to make," said a British government source quoted by the weekly. "I think we are at a tipping point in terms of the debate, as we were at a tipping point in 2004-2005 in terms of the science."
The Stern Review was commissioned by Britain's cabinet office and finance ministry a year ago to understand better the nature of the economic challenges and how they can be met in Britain and around the world.
The Observer said the cost of unchecked climate change would amount to up to 3.68 trillion pounds (5.48 trillion euros, 6.98 trillion dollars). Unless the world acts, it costs more than World War I, World War II and the Great Depression of the 1930s while rendering large parts of the planet uninhabitable, The Observer said.
Even if the world stopped polluting immediately, it said, the slow-growing effects of carbon already in the atmosphere would continue to warm the planet for another 30 years, with sea levels rising for a century.
The Observer said Stern forecasts that the world needs to spend one percent of its annual Gross Domestic Product, or about 184 billion pounds, to fight off global warming, or find the cost is between five times and 20 times higher.
Because the problem is so pressing, a successor to the Kyoto agreement on reducing greenhouse gases that cause climate change should be signed next year, rather than in 2010-2011 as planned, his report warns.
It calls for an international framework in a bid to stabilise not only temperatures but parts per million of carbon in the atmosphere. It would allow different countries to reduce emissions differently.
Britons, for example, face the prospect of a whole array of green taxes, such as on driving and flying.
But he stressed concerted international action was key, according to The Observer.
For example, if Britain shut down all its power stations immediately, he said, the reduction in global emissions would be cancelled out within 13 months by rising emissions from China.
The contents of Stern's report have been kept secret since being revealed to the world's environment ministers at a conference in Mexico earlier this month.
"He left no one in any doubt that doing nothing is not an option ... And he stressed that the need for action was urgent," an unnamed civil service source told The Independent on Friday.
The Independent said the finance ministry hoped Stern's report would turn the tide of public opinion in the United States, and dispute the American government's assertion that cutting carbon emissions was bad for economic growth.