London ? Raising the stakes in the global warming dispute with the United States and China, Britain issued a sweeping report Monday warning that the Earth faces a calamity on the scale of the world wars and the Great Depression unless urgent action is taken.

The British government also said Vice President Al Gore had agreed to provide advice on climate change – a clear indication of Prime Minister Tony Blair’s growing dissatisfaction with U.S. environmental policy. Gore has emerged as a powerful environmental spokesman since losing the 2000 presidential election.

The 700-page report argues that environmentalism and economic growth can go hand in hand in the battle against global warming. But it also says that if no action is taken, rising sea levels, heavier floods and more intense droughts could displace 200 million people by the middle of the century.

The report said unabated climate change would eventually cost the equivalent of between 5 percent and 20 percent of global gross domestic product each year. The report by Sir Nicholas Stern, a senior government economist, represents a huge contrast to the U.S. government’s wait-and-see policies.

Blair called for “bold and decisive action” to cut carbon emissions and stem the worst of the temperature rise.

Stern said acting now to cut greenhouse gas emissions would cost about 1 percent of global GDP each year. “The benefits of strong, early action considerably outweigh the costs,” he said. “We can grow and be green.”

U.S. response

Blair, Stern and Treasury chief Gordon Brown, who commissioned the report, emphasized that the battle against global warming can only succeed with the cooperation of major countries such as the United States and China.

President Bush kept the United States – 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.

Blair, Bush’s top ally in the Iraq war, has indicated U.S. policies on climate change are unacceptable.

Kristen A. Hellmer, deputy director for communications at the White House Council on Environmental Quality, said Bush “has long recognized that climate change is a serious issue, and he has committed the U.S. to advancing and investing in the new technologies to help address this problem.”

The United States, she said, “is well on track to meet the president’s goal to reduce greenhouse gas intensity of our economy 18 percent by 2012.”

Economic impact

Gore’s office said that in his unpaid role as an adviser, he would offer Britain’s Treasury his thoughts on developments in climate change science, new technologies for cutting emissions and ways of making the needed changes happen quickly.

Vicki Arroyo, director of policy analysis at the Pew Center on Global Climate Change in Arlington, Va., praised the report for trying to measure the cost of action and inaction against global warming. The report focused on the economic impact of climate change, and did not deal with any new scientific analysis.

“Economic assessments are inexact sciences, but they are used all the time in setting insurance rates and government regulation of highway safety, pollution control and food safety. They are projections of what the risks are and the benefits of averting those risks.”

Blair signed an agreement this year with California Gov. Arnold Schwarzenegger to develop 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 Earth.

The Stern report praised states such as California for developing their own objectives and policy frameworks regarding the battle against global warming.

The report said at current trends, average global temperatures will rise by 3.6 degrees to 5.4 degrees within the next 50 years or so, and the Earth will experience several degrees more of warming if emissions continue to grow.

It said such warming can have severe impact, including melting glaciers, rising sea levels, declining crop yields, drinking water shortages, higher death tolls from malnutrition and heat stress, and widespread outbreaks of malaria and dengue fever. Developing countries often would be the hardest hit.