By Roger Harrabin
Environment analyst, BBC News, Monterrey
Climate talks between the world's top 20 polluters have ended with an unusual level of agreement on the urgent need to tackle greenhouse gas emissions.
The US remains one of the highest emitters of polluting gases
But delegates at the Mexico talks also stressed the massive gap between the politics and science of climate change.
Several said they had never known such a positive atmosphere. Nobody doubted the reality of climate science anymore.
The UK claimed the talks a success, saying they brought together ministers from developed and developing nations.
Politicians from China, India, Brazil, Mexico, South Africa, Indonesia and other growing nations sat alongside G8 members to hear presentations on climate science, economics, technology, business and policy.
For all the positive mood of the meeting, it is hard to be optimistic
Business leaders from the World Economic Forum in Davos expressed a need for strong targets from governments on greenhouse gases.
There was a clear message from the International Energy Agency (IEA) and British government-backed economist Sir Nicholas Stern that it was better - and cheaper - to cut greenhouse gas emissions now than to wait for the climate to change then try to adapt.
The IEA said much could be achieved with existing technology, although far greater investment was needed.
The World Bank outlined its framework for investment in clean technology to help developing countries expand energy supplies without having to follow the dirty path of the West.
But Bank representatives made it clear that there was no sign of the $20bn (£10.6bn) investment programme heralded by the UK Chancellor Gordon Brown.
The US, which was present at the talks, is objecting to parts of the proposal.
The Under-Secretary of State for Global Affairs, Paula Dobriansky, told the BBC that the US was now acting urgently to tackle greenhouse gases - then later admitted that the country's emissions would continue to rise.
Another US delegate agreed that the world would face inevitable sea-level rise because of climate change. But when informally asked if the US opposition to mandatory CO2 cuts had changed in any way in response to a surge in concern over recent science of climate change, economically replied "no".
There have been rumours in the US media that the Department of Energy has been in talks with business about mandatory CO2 caps.
But a source here in Monterrey said the White House Council on Environmental Quality (a hard-line group of advisers with close links to the US oil industry) has ruled that out.
The US is by no means the only sticking point in climate talks, however.
The Russians - who hope they will benefit from a warmer world - did not attend the Monterrey talks.
It is rumoured that their invitations were sent too late because of recent political turmoil in Mexico.
The Chinese were present, outlining ambitious plans to match their concern on climate with a big programme of investment in energy efficiency.
Climate change could wipe out economic growth in some regions
But the Indians despatched only their concerned environment minister, instead of their unconcerned energy minister who has far more sway over India's emissions.
So, for all the positive mood of the meeting in this spectacular northern Mexican city, surrounded by towering limestone mountains, it is hard to be optimistic.
The UK Environment Secretary David Miliband said there had been real and practical progress but warned that the pace of action had to be much faster or CO2 emissions by 2050 would be 137% higher than in 2003.
"Business as usual", he said, was not an option.
One delegate told me he thought the pace of political ambition on emissions was so slow that we had a 1,000-1 chance of avoiding dangerous climate change.
He later sent me a text message to assert that he had been overly pessimistic. The odds, he said, were only 100-1.
The chances were bad, he said, but it was still worth fighting on.