British Environment Secretary Margaret Beckett, in a speech to open the three-day meeting of more than 100 scientists, said all countries emitted greenhouse gases and so the problem required an international response.

"A significant impact (on the world's climate system) is already inevitable," she said.

"What is certainly clear is that temperatures will go on rising... most of the warming we are expecting over the next few decades is now virtually inevitable."

Beckett warned: "No one country, not even one continent, can solve the problem by acting alone."

She hailed the Kyoto Protocol, the UN's pact on carbon pollution, which takes life on February 16 after more than seven years of haggling to complete its rulebook and secure its ratification.

"Kyoto is very much a first step"," said Beckett, who also lobbied for clean technology and encouragement for developing countries not to follow rich nations down the path of fossil-fuel pollution.

Analysts say the prospects for Kyoto are clouded at best, given that it lacks the United States, the world's No. 1 carbon polluter.

US President George Bush declared in 2001 that the deal was too expensive for the oil-dependent American economy.

Beckett admitted it was "out of the question" for Washington to return to Kyoto after this walkout, but "we would like to see America engaging very much more fully" in international cooperation on carbon pollution.

The Exeter conference, "Avoiding Dangerous Climate Change," gathers more than 100 scientists from 30 countries.

The forum has been called by President George W. Bush's closest political friend, British Prime Minister Tony Blair, who as president of the Group of Eight (G8) countries has been lobbying Washington to do more on tackling climate change.

It is the biggest scientific confab on greenhouse gases since the publication in 2001 of a report by the UN's top expert group, the Intergovernmental Panel on Climate Change (IPCC).

That report -- next to be updated in 2007 -- calculated that, by 2100, temperatures would rise by between 1.4 Celsius (2.5 Fahrenheit) and 5.8 C (10.4 F) compared to 1990 levels, driven by atmospheric carbon pollution which stokes up heat from the Sun.

More than three dozen papers are to be presented in Exeter, and they will be synthesised in a set of conference conclusions that will be submitted to the Group of Eight (G8) nations, currently chaired by Britain.

But there will not be any recommendations for policymakers, said conference chairman Dennis Tirpak.

The studies range from highly technical reports on improving computer models to predictions about the impact of climate change on crops, biodiversity, disease and apocalyptic scenarios involving runaway global warming.

The Kyoto Protocol requires industrialised signatories -- excluding the United States, which rejected the deal in 2001 as too costly for the oil-dependent US economy -- to trim output of six greenhouse gases by a deadline of 2008-2012.

At best, without the United States, the biggest single carbon polluter, Kyoto will shave two or three points of the predicted 30-percent rise in global CO2 emissions between 1990 and 2010.

But scientists say this effort is puny compared to what is needed to stave off potentially catastrophic and enduring damage to the climate system.

The European Union (EU) has suggested the world strive to keep the additional rise down to less than 2 C (3.6 F) through pollution controls.

But IPCC chairman Rajendra Pachauri told the conference that climate science was still in its infancy. No-one can say with certainty what a safe figure would be, not least because some regions could be worse hit than others, he warned.

"Can a temperature target capture the limits of what is dangerous?" he asked.

Even if today's emissions were immediately stopped, temperatures will continue to rise for generations to come because of the gas which has already been spewed into the atmosphere, Pachauri said.

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