Introducing the report, Prime Minister Tony Blair said unabated climate change would eventually cost the world the equivalent of between 5 percent and 20 percent of global gross domestic product each year. He called for "bold and decisive action" to cut carbon emissions and stem the worst of the temperature rise.
CBS News reporter Larry Miller says the primary message of the report is act now, or pay later.
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.
"That is manageable," he said. "We can grow and be green."
Blair, Stern and Treasury chief Gordon Brown, who commissioned the Stern report, emphasized that the battle against global warming can only succeed with the cooperation of major countries such as the United States and China.
The report by Stern, a former chief World Bank economist, represents a huge contrast to the U.S. government's wait-and-see global warming policies.
U.S. President George W. Bush kept America — by far the biggest emitter of carbon dioxide and other gases blamed for global warming — out of the Kyoto international treaty to reduce greenhouse gases, saying the pact would harm the U.S. economy. The international agreement was reached in Kyoto, Japan, in 1997 and expires in 2012.
Brown, who is expected to replace Blair as prime minister next year, announced Monday that former U.S. Vice President Al Gore, who has emerged as a powerful environmental spokesman, would advise the British government on climate change.
The Stern report praised U.S. states such as California for developing their own objectives and policy frameworks regarding the battle against global warming.
Blair signed an agreement this year with California Governor Arnold Schwarzenegger to develop new technologies to combat the problem. The measure imposed the first emissions cap in the United States on utilities, refineries and manufacturing plants in a bid to curb the gases that scientists blame for warming the planet.
But no matter what Britain, the United States and Japan do, the effort to reverse global warming cannot succeed without cooperation from such fast-industrializing giants as China and India, the report said.
"Britain is more than playing its part. But it is 2 percent of worldwide emissions," Blair said. "Close down all, 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. We have to act together."
Stern's 700-page report said that, at current trends, average global temperatures will rise by 3.6 to 5.4 degrees Fahrenheit within the next 50 years or so, and the earth will experience several degrees more of warming if the emissions continue to grow.
It said such warming can have severe impact, including melting glaciers, rising sea levels, declining crop yields, new shortages of drinking water, higher death tolls from malnutrition and heat stress, and more widespread outbreaks of malaria and dengue fever. Developing countries often would be the hardest hit.
Stern's report, a major effort to quantify the economic cost of climate change, said evidence showed "that ignoring climate change will eventually damage economic growth."
"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," it said.
The report acknowledged that its predictions regarding GDP used calculations that had to rely on sparse or nonexistent observational data about high temperatures and developing countries, and to place monetary values on human health and the environment, "which is conceptually, ethically and empirically very difficult."
Stern said the world must shift to a "low-carbon global economy" through measures including taxation, regulation of greenhouse gas emissions and carbon trading.
He said the world must halt deforestation, step up development of technology aimed at clean power, heat and transportation, eventually make deep cuts in the transport sector, and develop extensive ways of capturing and storing greenhouse gas emissions.
The British government is considering new "green taxes" on cheap airline flights, fuel and high-emission vehicles.
Blair said the scientific community agreed that the world was warming, and that greenhouse gas emissions were 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."
Blair said some of the world's big oil companies had showed an interest in combating global warming, but that they weren't going to do it until there was a "legally binding international framework" impelling them to act.
Stern is scheduled to discuss his report next week with the annual U.N. Climate Change Conference in Nairobi, Kenya.