LONDON — Unchecked global warming will devastate the world economy on the scale of the world wars and the Great Depression, a major British report said today.

British Treasury chief Gordon Brown, who commissioned the report, said former U.S. Vice President Al Gore, who has dedicated much time to warning of the effects of global warming, would advise the British government on climate change.

Introducing the report, British Prime Minister Tony Blair said unabated climate change would eventually cost the world between 5 percent and 20 percent of global gross domestic product each year.

He called for "bold and decisive action" to cut carbon dioxide emissions and stem the worst of the temperature rise.

The report is expected to increase pressure on the Bush administration — which never approved the Kyoto Protocol climate-change accord — to step up its efforts to fight global warming.

Report author Sir Nicholas Stern, a senior government economist, said that acting now to cut greenhouse gas emissions would cost about 1 percent of global GDP each year.

"The evidence shows that ignoring climate change will eventually damage economic growth," said Stern's 700-page report, an effort to quantify the economic cost of climate change.

"Our actions over the coming decades could create risks of major disruption to economic and social activity, later in this century and in the next, on a scale similar to those associated with the great wars and the economic depression of the first half of the 20th century," he added.

Blair said the scientific community agrees that the world is warming, and that greenhouse gas emissions are largely to blame.

"It is not in doubt that if the science is right, the consequences for our planet are literally disastrous," he said. "This disaster is not set to happen in some science fiction future many years ahead, but in our lifetime."

"Unless we act now ... these consequences, disastrous as they are, will be irreversible," he added.

Stern said the world must shift to a "low-carbon global economy" through measures including taxation, regulation of greenhouse gas emissions and carbon dioxide trading.