"The choice at the summit is a weak agreement or no agreement at all," said Elliot Diringer, a director of the Washington-based Pew Center, an environmental think-tank.

"There is no indication that the Bush administration is willing to move in any significant way," he said of the Scotland summit, where climate change and aid to Africa are top themes.

British Prime Minister Tony Blair, the host, says that greenhouse gases from human activities may cause catastrophic floods, heat waves and storms that could drive many species to extinction and push up sea levels by a metre (three ft) by 2100.

He calls climate change "probably, long-term the single most important issue we face as a global community" -- eclipsing threats like poverty, AIDS or terrorism.

But a leaked draft of a final statement for the summit underscores a gulf between Bush and Blair about the extent of the problem. It includes no firm targets, timetables or cash.

WORLD WARMING

In a June 14 draft, the sentences "Our world is warming" and "We know that the increase is due in large part to human activity" are in brackets, indicating US disagreement.

Many scientists are aghast -- the science academies of all G8 nations as well as of China, India and Brazil said this month that burning of fossil fuels in power plants, cars and factories seemed the main cause of recent warming.

"I think the consensus is very, very strong and very compelling that we are on a warming trend," said Rajendra Pachauri, chairman of a panel of more than 2,000 scientists that advises the United Nations on climate policy.

"I do not despair," he added, pointing to measures by US states and companies to cut emissions of carbon dioxide, the main greenhouse gas, and EU markets where industries trade carbon dioxide allowances as part of a long-term scheme to cut emissions.

Environmentalists hail Blair's drive against climate change, even though it always seemed wishful thinking that Washington might repay Blair's support for the 2003 war in Iraq by joining other G8 countries in capping greenhouse gas emissions.

"We think it's very important that (Blair) stands up to President Bush just as he did to other leaders in the European Union budget debate," said Jennifer Morgan, climate expert at the WWF conservation group.

Blair is isolated in an EU row about the bloc's finances.

Morgan said that Blair should ignore Bush and work with China, India, Brazil, Mexico and South Africa, whose leaders will also attend, to start mapping out long-term climate goals.

G8 nations Japan, Germany, Britain, France, Italy, Canada and Russia have all signed up for the UN's Kyoto protocol, which aims to cut emissions of carbon dioxide by 5.2 percent below 1990 levels by 2008-12.

Bush pulled out in 2001, saying Kyoto would be too costly and wrongly excluded developing nations. And the US Senate on Wednesday rejected a less demanding plan to cut US emissions below 2000 levels by 2010, by 60-38 votes.

However, the Senate did agree a non-binding resolution calling for a mandatory cap-and-trade system to cut emissions.

Some scientists, mainly in the United States, argue that warming may be an illusion caused by expansion of heat-generating cities. A warmer world might create more clouds that would reflect heat from the sun back into space.

"Surface warming is nothing to be worried about," said Fred Singer, head of the US Science and Environmental Policy Project. Bush's policies include $5.2 billion in spending in 2005 on climate and energy research and energy tax incentives.

Harlan Watson, the chief US climate negotiator, said a US drive to clean carbon dioxide emissions from coal -- now one of the dirtiest fuels -- and US energy security were reasons to oppose emissions caps.