By Richard Black
BBC environment correspondent, in Exeter
It is inevitable global warming will have a major impact on our planet, the UK's environment secretary says.
Beckett: Temperatures are set to rise still further
Margaret Beckett opened a conference on climate change on Tuesday, urging major international co-operation to prevent more serious, future temperature rises.
The meeting, held at the Met Office in Exeter, is intended to look at what constitutes "dangerous" climate change.
"What is certainly clear is that temperatures will go on rising," Mrs Beckett told the assembled delegates.
"Most of the warming we are expecting over the next few decades is now virtually inevitable."
Because it takes decades for greenhouse gases such as carbon dioxide (CO2), methane and nitrous oxide to break down in the atmosphere, some warming would result even if production of these gases could be returned to pre-industrialised levels overnight.
In fact, production of these gases is increasing, and so are their levels in the atmosphere; the carbon dioxide concentration is roughly 30% more than in pre-industrial times.
This conference has been called to answer a deceptively simple question: how much is too much? Or to pose it more scientifically: what levels of greenhouse gases would bring significant and possibly irreversible damage to natural ecosystems and human society?
The European Union has suggested that a 2C rise in average global temperatures would be too much, and the world community ought to strive to keep levels below this threshold.
Rights and climate
"It's a very complex issue and it's an evolving science," the Chair of the Intergovernmental Panel on Climate Change (IPCC), Dr Rajendra Pachauri, told the BBC News website.
"You have to decide what is dangerous for whom; and I think that if we are looking for global solutions, we can't possibly ignore even the smallest communities on the face of this Earth.
"If the impacts of climate change are going to restrict the choices that people normally would have, to pursue their lives and livelihoods in the manner that they want, then, to that extent, climate change and its impacts impose an infringement on their human rights."
Computer models produce far from certain simulations
All the scientists speaking here acknowledged the huge uncertainties present in trying to predict the precise relationship between carbon dioxide concentrations and temperature rise.
It was exemplified last week with the release of a vast study in climate modelling, climateprediction.net, which showed that if the concentration of CO2 were to double, the global rise in average temperatures could be anywhere between 2 and 11C.
But if governments are to live up to the wording of the United Nations Climate Change Convention (UNFCCC), agreed at the Earth Summit in Rio de Janeiro in 1992, they have to take measures to avoid "dangerous" climate change.
So, somehow, a consensus has to be reached about what "dangerous" actually means.
"One of the things that we hope comes out of the scientific conference is some kind of assessment of what that means," said Mrs Beckett, "because obviously it will be a different impact in different sectors and regions, and obviously it is crucial to people in thinking about how they can prepare; how they can adapt."
Stressing that international action is vital, Mrs Beckett said the British government was engaged in a dialogue with President Bush in an attempt to change the US isolationist stance on climate change.
But in the face of repeated questioning, Mrs Beckett could offer no evidence that the Bush administration was taking the message on board.
The conference chair is Dennis Tirpak, of the UNFCCC.
He offered a sober analysis of the size of the task facing scientists and politicians convinced of the pressing need to tackle carbon emissions.
"The International Energy Agency in its World Energy Outlook for 2004 gave us a glimpse of just the next 25 years," he said.
Environmentalists are demonstrating outside the meeting
"In this short time, world electricity demand is projected to double, with fossil fuels supplying most of this need.
"In this time period, emissions of carbon dioxide from all sectors, including electricity, are likely to increase by 62%."
Whatever the details, the niceties, the caveats of the positions taken by delegates here, most would probably agree that 62% fits within the definition of "dangerous".