The US is the biggest emitter of carbon dioxide and other gases blamed by scientists for global warming.
Under the Kyoto pact, 35 industrial nations have agreed to cut their gas emissions by 5 per cent on average below 1990 levels by 2012.
The Bush administration has instead pledged a commitment to advancing and investing in new technologies to combat global warming.
It has set a goal of reducing "greenhouse gas intensity", which measures the ratio of greenhouse gas emissions to economic output, by 18 per cent by 2012.
"We have to look at the numbers because that's all that counts in the end"
Jeffrey Sachs, senior economist
Jessica Emond, a spokeswoman for the US environmental protection agency, said: "Our voluntary programmes are working. In 2005, our voluntary partnerships prevented over 85 million metric tonnes of greenhouse gas emissions."
China announced this month that it will spend more to research global warming, but said it lacks the money and technology to significantly reduce greenhouse gas emissions.
Sachs said the two countries need to take more forceful action quickly, especially in light of a key meeting of environmental ministers scheduled for December in Bali to begin talks on what action is required after the Kyodo protocol expires in 2012.
"I see it as impossible in our current political environment for a [presidential] candidate not to have a clear and strong position on limiting greenhouse gases in the US."
Nancy Pelosi, the leader of the US House of Representatives, announced plans last month to create a special committee on global warming.
John McCain, a Republican senator, and Barack Obama, a Democratic senator, both presidential contenders, are sponsoring a bill that would cut emissions by two-thirds by 2050.
Sachs said: "We have to look at the numbers all the time, not just the direction, not the sentiment, not the announcements.
"We have to look at the numbers because that's all that counts in the end."