LONDON — A major study issued Monday concludes that without rapid and substantial spending, global warming will reduce worldwide productivity on the scale of the Great Depression, devastate food sources, cause widespread deaths and create hundreds of millions of refugees.
The report commissioned by the British government, which officials called the most comprehensive review of the economics of climate change, warns that failure to act could cost up to 20% a year in lost income worldwide. Acting now, however, could bring about meaningful control of greenhouse gases at an annual cost of 1% of global gross domestic product, it says.
The findings appear to counter the long-standing argument of the Bush administration that controlling greenhouse gases is costly and possibly ineffective.
However, the savings would occur only with the kind of rapid and comprehensive international cooperation on the issue that so far has proved elusive.
British officials said they would take immediate action to legislate carbon-reduction targets, push expanded international carbon-trading programs and move toward reducing carbon emissions in Europe by 30% by 2020 and 60% by 2050. Carbon trading allows companies to exceed emission limits by buying credits from those that are below their emission targets.
Prime Minister Tony Blair, calling the report by senior government economist Nicholas Stern "a landmark in the struggle against climate change," warned that there was a limit to what Britain alone could do.
"Britain is more than playing its part," Blair said. "But it is 2% of worldwide emissions. Close down all of Britain's emissions and in less than two years, just the growth in China's emissions would wipe out the difference. So this issue is the definition of global interdependence."
But the report's findings show that "if the science is right, the consequences for our planet are literally disastrous," Blair said. "And this disaster is not set to happen in some science-fiction future, many years ahead, but in our lifetime."
In Washington, the National Oceanic and Atmospheric Administration, the lead U.S. agency on global warming, had no immediate comment on the British report. Agency spokesperson Jana Goldman said officials could not react to the report until they had read it.
The report examines the consequences of acting -- or failing to act -- to control rising temperatures due to greenhouse gases from deforestation and fossil fuels.
The current level of greenhouse gases is already 54% higher than it was before the Industrial Revolution, and could be double that level as early as 2035, the report suggests. Such an increase could raise temperatures by more than 3.6 degrees Fahrenheit by mid-century and a disastrous 9 degrees by century's end, it says.
The result would be melting glaciers that trigger floods and reduce snowpacks that supply drinking water, threatening a sixth of the world's population, the report says. Other effects would include reduced crop yields, leaving hundreds of millions of people unable to produce or purchase sufficient food; an increase in vector-borne diseases; up to 200 million people displaced because of rising sea levels and drought; and the possible extinction of 15% to 40% of species.
"The report sets out I think very clearly that this is not just an environmental issue, or even just an economic issue, but it is a security issue," Foreign Secretary Margaret Beckett said. "There are some people all over the world who still believe there can be some kind of trade-off between economic and climate security. I think this report knocks [that notion] on its head."
Stern, a former chief economist for the World Bank, said the study found that it was still possible to achieve meaningful temperature controls at a cost equivalent to consumers paying an average of 1% more for everything they buy, and substantially less than the cost of failing to act.
"That's manageable," Stern said. "We can grow and be green."
The report calls for using taxes and regulations to make carbon use more costly, policies supporting low-carbon technology, and changing the public's attitude toward energy efficiency.
Air carriers and utilities could be among those hit hardest by any new emissions-reduction laws. Already, Britons are looking at a possible end to bargain-basement fares to the Continent and higher prices for out-of-season and exotic vegetables from the tropics.
Poor countries will bear the brunt of the effects of climate change, the report says, but it suggests that rich countries must bear 60% to 80% of the responsibility for emissions reductions.
"The conclusion of the review is essentially optimistic. There is still time to avoid the worst impacts of climate change if we act now and act internationally," Stern said. "But the task is urgent. Delaying action, even by a decade or two, will take us into dangerous territory. We must not let this window of opportunity close."
Times staff writer Joel Havemann in Washington contributed to this report.