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 Monday.

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.

British Treasury chief Gordon Brown, who commissioned the Stern report, said former Vice President Al Gore, who has emerged as a powerful environmental spokesman, would advise the British government on climate change.

[Separately, a United Nations agency reported on Monday that greenhouse gas emissions among industrialized countries began rising again in recent years after falling during the 1990s. Though emissions overall are more than three percent below where they were in 1990, the data released yesterday indicated that progress stalled over the last four years as the Russian economy began growing, and some transitional nations like Turkey experience a rapid growth greenhouse gas output.

After falling from the equivalent of around 20.5 tons to 19.5 tons of carbon dioxide between 1990 and 2000, emissions between 2000 and 2004 rose to 19.7 tons. The study covered 41 industrialized countries, including Eastern European nations that are designated as economies in transition. It did include the United States and other industrialized nations that are not a party to the Kyoto Protocol on climate change, but did not cover emerging economic forces such as China, India and Brazil.]

The author of the British report, 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 emission trading.

Brown said Britain would lead the international effort against climate change, establishing "an economy that is both pro-growth and pro-green."

He called for Europe to cut its carbon dioxide emissions by 30 percent by 2020 and 60 percent by 2050.

The British government is considering new "green taxes" on cheap airline flights, fuel and high-emission vehicles.