By Richard Black
BBC environment correspondent, in Exeter
The risks from global warming are more serious than previously thought, a major climate conference has concluded.
In its final report, the committee which organised the UK Met Office meeting said the impacts of climate change were already being felt.
The communiqué held back from declaring precisely what was meant by a "dangerous" level of warming.
But, "it has given us a clearer picture of what is expected," said Environment Secretary Margaret Beckett.
The conference in Exeter, in southwest England, was called "Avoiding Dangerous Climate Change".
It was announced by Prime Minister Tony Blair, and was intended to give a scientific context to Britain's efforts to make the climate issue a central feature of its Group of Eight (G8) and EU Presidencies this year.
Although the committee refrained from defining "dangerous", it did emphasise the scale and nature of the warming threat it said was already apparent.
"The impacts of climate change are already being observed," the communiqué said.
"Ecosystems are already showing the effects of climate change. Changes to polar ice and glaciers and rainfall regimes have already occurred."
The European Union had previously suggested trying to limit any rise in average global temperatures to 2C, but Dr Bill Hare, from the Potsdam Institute for Climate Impact Research, Germany, who presented the conference with a worldwide survey of global impacts, said even this rise was too much.
"You know, I think the European target is really an upper limit, actually - I think the science is showing that that may even be too high in the long term," he told the BBC News website.
"I think we have to keep temperatures below that level, otherwise we risk really major changes."
Good and bad
A rise of 2C, according to research presented here, would mean the displacement of millions of people from their homes, a fall in the productivity of farmland, widespread devastation of coral reefs and other vulnerable ecosystems, and melting of the Greenland ice cap.
But keeping the temperature rise below 2C will mean adopting a wide range of measures - as the committee puts it, there is "no magic bullet".
Energy efficiency, emissions trading, and new technology must all be used, they said, and quickly - the costs of preventing climate change rise the longer action is delayed, they argued.
It some respect, the final communiqué went further than the last United Nations' benchmark report on the nature of global warming, issued by the Intergovernmental Panel on Climate Change in 2001.
"In many cases, the risks are more serious than previously thought. As noted in the Third Assessment Report, changes up to 1C may be beneficial for a few regions and sectors, such as agriculture in the mid to high latitudes.
"A number of new impacts were identified that are potentially disturbing."
And the chair of the Exeter steering committee, Dennis Tirpak, who co-ordinates climate change activities at the Organisation for Economic Co-operation and Development (OECD), added: "We hope politicians will now begin to rethink where we're going on this issue.
"What we're trying to provide is a snapshot of the evidence - and we have accumulated a body of evidence that we're going to need both adaptation and mitigation."
The UK government has welcomed the report. Mrs Beckett said it underlined the need for urgent international action.
Ministers will now take its conclusions to meetings with governments of the G8 group of nations due later this year, where their major task will be to persuade the United States to join the "international consensus".
"Science on its own cannot give us the answer to the question of how much climate change is too much," she said.
"What it can do, however, is set out the consequences of allowing different degrees of climate change to continue in order to guide the choices that we must take."