The deal would be very useful just on its own: together, the two countries account for 40per cent of the world's greenhouse gas emissions. But if the US-Chinese agreement can become the model, with other rich countries accepting the same terms as the US and other rapidly developing countries making the same commitments as China, we might actually end up in December with a global deal worth having.

Work on the bilateral deal began in the dying days of the Bush administration, with the initiative on the Chinese side coming from the vice-chairman of the National Development and Reform Commission, Xie Zhenhua. On the American side the driving forces were John Holdren and the director of the energy and climate program at the Carnegie Endowment for International Peace, Bill Chandler. It is not a done deal yet, but Chandler predicts it will happen by autumn, and that it will be ''serious'' and ''substantive''. The draft agreement, drawn up by Holdren and Chandler late last year, has three main points: the US and China will use existing technologies to cut carbon emissions by 20 per cent by 2010; they will cooperate on new technologies including carbon capture and storage and better fuel efficiency in vehicles; and they will both join the global agreement in Copenhagen in December. This US-Chinese draft has not been signed, but Xie has agreed to it.

A deal like this will not end the climate crisis, even if all the other big emitters accept similar terms. Past emissions have already committed us to so much warming that there will be famines, waves of refugees and wars in some of the worst-hit regions no matter what we do now.

Nevertheless, the kind of treaty that the US-Chinese deal might lead to in Copenhagen in December is worth having, because if we move fast enough there is still time to preserve most of the world we know in a more or less recognisable form.

Twentyper cent across-the-board cuts in emissions by 2010, or even by 2013, would be an excellent start. In the meantime, Obama has just cut a deal with the automobile industry on fuel efficiency that will make a real difference to American emissions.

With the highest rate of car ownership in the world (five cars for every six people) and the world's worst fuel efficiency, US cars emit much more carbon dioxide per year than all the cars in Japan, China, India, Russia, France, Italy, Germany, Britain and Canada put together.

The target first set by Governor Arnold Schwarzenegger in California, an average of 35.5 miles per gallon (6.62 litres/100 km) for all cars and light trucks by 2016, has now been adopted by President Obama for the whole country. That will eventually cut US vehicle emissions by 40per cent (current average mileage for US vehicles is only 21.4). It also means that US oil imports may fall by up to half over the next 10 years.

By the time the US reaches its 35.5mpg target in 2016, most other countries in the world will have moved on to an average of 45mpg or better. (China's current requirement is 43mpg, and the European Union's target is 47mpg by 2012.) Having left everything so late, the US will be playing catch-up for a long time but at least it is back in the game. And China is finally talking about cutting its emissions, too.

Governor Schwarzenegger's environmental adviser, Terry Tamminen, who was at the talks in China, said, ''There are these two countries that the world blames for doing nothing, and they have a better story to tell.''

Things are moving in the right direction at last.

Gwynne Dyer's latest book, Climate Wars, was published recently in Australia by Scribe.