Washington

Warm words: in the wake of a US drought, John McCain (inset) speaks out on climate change. Credit: JOE RAEDLE/MICHAEL SMITH/NEWSMAKERS

Advocates of action to tackle climate change won an influential ally last week, as Senator John McCain's (Republican, Arizona) Senate Commerce Committee heard leading scientists testify that humankind is causing significant global warming.

Other congressional hearings in recent years have pitched global warming ‘sceptics’ against the larger group of climate scientists who believe that greenhouse-gas emissions are contributing to climate change — creating the impression that researchers are in disarray. But McCain's hearing presented a more sober picture of the evidence.

Neal Lane, Bill Clinton's scientific adviser, said there was now “a significant consensus” on the issue. “Basically, the debate has changed from 'are we warming the Earth?' to ‘how much are we warming the Earth?’,” Lane said.

Each of the five scientific witnesses called before the hearing repeated this perspective. These included John Christy, a climate scientist at the University of Alabama, who has sometimes been sceptical about the human component of climate change.

McCain, who recently failed to win the Republican nomination for this November's presidential election, said the hearing was a response to concerns encountered on the campaign trail.

“In town-hall meeting after town-hall meeting, young people would stand up and say: ‘What is your position on global warming?’,” McCain said. “I don't have a plan, but I do believe that policy-makers should be concerned about mounting evidence of global warming.”

Environmentalists greeted his approach as further evidence that the tide of US opinion is slowly turning in favour of action to limit greenhouse-gas emissions.

In the past year, major corporations including Ford, General Motors and DuPont have withdrawn their support from the Global Climate Coalition, which has campaigned against such action. Some of these corporations have also set their own internal targets for reducing emissions.

Until McCain's hearing on 17 May, Congress had not reflected this shift. It is trying to prevent the US government spending money on carbon-emission trading schemes or other components of the Kyoto Protocol. The Clinton administration, which signed the protocol, has not asked the Senate to ratify it, knowing it would refuse.

Drafts of the third assessment report of the Intergovernmental Panel on Climate Change, to be published next year, state that human activities are contributing to global warming.

The US government, meanwhile, is set to publish its own national assessment of the consequences of climate change next month. This is intended to influence the debate by showing Americans the relevance of the problem, but some industrial groups have already questioned its neutrality.

The next conference of the parties to the Kyoto Protocol will take place in The Hague in November, a week after a presidential election that will help to determine the United States' position. Whatever happens, advocates of the Kyoto Protocol do not envisage the US Senate ratifying it before 2003.