That the US will convene a series of meetings of the world's most polluting countries to discuss action on climate change. By the end of next year, it says, these countries will agree and set a long-term goal to reduce greenhouse gases. Each country will also have an interim national target and they will cooperate to promote clean technology.
2 Why is it being seen as so important?
The science on climate change is clear: human emissions of carbon dioxide and other greenhouse gases are rapidly warming the planet. The UN's Intergovernmental Panel on Climate Change (IPCC) says we could have fewer than 10 years in which to start to bring levels of pollution down, if we are to avoid the worst effects over the coming century. The world's only international treaty that compels countries to act, the Kyoto protocol, runs out in 2012. If a replacement is not agreed soon, analysts fear a collapse of the emerging carbon markets set up under Kyoto - the only realistic large-scale way to bring down carbon pollution found so far. That would put attempts to control emissions back to square one and make it almost impossible to act in time.
The US is seen as the key to a new agreement. President Bush has no time for Kyoto-style carbon caps - binding limits on countries' carbon emissions - which he claims would damage the US economy. His team has regularly tried to obstruct and delay attempts to set up a post-Kyoto deal. China and India are keen to be involved in such a deal, on non-binding terms, but want the US to play ball.
3 He has been pressured to change his position, so does this represent a shift?
Yes and no. The language the president used yesterday on new frameworks and setting global goals would have been unthinkable a year ago. During UN negotiations in Montreal in 2005, the US team stormed out when the idea was raised. Gone are the questions about the science and the emphasis on the uncertainties, replaced with an explicit acknowledgement that climate change is a serious problem. As Stephen Hale, head of the Green Alliance, puts it: "Every shift from George Bush on climate change, however small, is to be celebrated." That is certainly the view of Downing Street, which last night hailed Mr Bush's words as an important step.
But is it a step forward? Green campaigners were less confident. They are concerned that the US appears to have snubbed the existing negotiations and set up a parallel process. Tony Juniper, of Friends of the Earth, said: "He had to respond and his way of responding is to create these meetings as a way of giving the impression of doing something right up until he leaves office. He's stuck two fingers up at Tony Blair and if I was in Downing Street, then I'd be furious."
There was little detail from President Bush on what the global goal would be, despite the scientists saying for several years that it would be dangerous for the planet to experience much above a 2C rise, adopted by countries including Britain and Germany as their nominal target. And he made no mention of carbon trading, which Downing Street sees as the way to involve rich and poor nations on an equal footing, but which requires some form of cap on pollution to work.
4 What does the US think it can achieve with this announcement?
A charitable explanation of yesterday's announcement is that it is President Bush's way of trying to make progress by a route other than Kyoto. He has long talked up the benefits of technology and there were significant nods yesterday to renewable energy and alternative fuels. And his talk of industrial sectors coming together mirrors a British idea to establish carbon markets along such lines. Following the 2005 G8 summit at Gleneagles, the US, Australia and others announced they were setting up a partnership to voluntarily develop new technologies.
Critics point out two flaws in such a strategy. Firstly, much of the technology needed to bring down emissions such as more efficient engines and green ways of generating electricity exist. The third report from the UN's IPCC this month, which the US government signed up to, said as much - the big question is how to make it more widely used. Secondly, it could be asking a lot for companies, organisations and individuals to choose to do the right thing voluntarily. The whole point of Kyoto was to impose expensive caps on pollution from industry to force them to invest in cleaner equipment. Most experts believe such caps will be needed to drive through behaviour change in future. The UK's environment secretary, David Miliband, envisages every sector of society covered by such cap and trade schemes, down to individuals carrying carbon ration cards.
Robin Oakley, of Greenpeace, said the president's plan was "designed to kick this issue into the long grass until he leaves office". He said: "Bush should take his cue from an increasing number of states, such as California, and engage with the international community by committing to deep mandatory cuts in carbon emissions now, not voluntary cuts at some unspecified point in the future."
5 Will it help the fight against global warming?
The planet's thin later of atmosphere does not care where the carbon pollution comes from. The only way the president's announcement will help is if it cuts emissions. The scientists are clear on what will happen if we don't.
So will it help to do that? It took years for international politicians to hammer out the Kyoto framework, the world's first and largely ineffective attempt to regulate carbon pollution, and there must be serious doubts about President Bush repeating the trick in fewer than 18 months. Still, it is rarely a bad idea for countries to get together to discuss ways to tackle global warming, especially if China and India are involved, as Mr Bush said they would be.
The US yesterday denied claims that its process had been set up to undermine existing talks, saying that its outcome would feed back into them. But some still worry about Mr Bush's motives. "Given his track record on this subject, putting Bush in charge of talks on climate change is like King Herod opening a nursery," said Stephen Hale.
6 Weren't the G8 and UN working this out? Where does it leave them?
It leaves them somewhat sidelined. The German hosts of the G8 summit next week had hoped that the rich nations' club would agree to a set of principles for combating climate change, that would most importantly include a commitment to keep the rise in the Earth's temperature to 2C. Mr Bush made no reference to this meeting. The G8 commitment was intended to set the scene for a critical UN-brokered meeting in Bali in December to work out a successor to the Kyoto protocol. The Bali meeting is the latest in the UN's annual series (which in 1997 spawned Kyoto) and was being billed as the Earth's last chance to control its climate, almost certainly using mandatory emissions goals. President Bush is proposing creating an alternative to this process, probably involving the voluntary approach he favours. US officials said the two tracks would run in "parallel", but it is not clear what the advantages of such duplication would be.
7 What next?
To Germany for next week's G8 summit, which will reveal the US's true thinking. Leaked documents have suggested President Bush's team will object to any agreement on specific goals, timetables and carbon-trading schemes. Tony Juniper said: "It's a classic spoiling tactic from the Americans. Now whenever an issue is raised at the G8 which they don't like the look of they can fold their arms, not get involved and say they are going to talk about it at one of these new meetings next year."