The White House acknowledged yesterday that the “global challenge” posed by climate change “requires global solutions”, but once again sought to play down some of the most apocalyptic forecasts.

The comments from Sharon Hays and Jim Connaughton, senior White House officials on the environment, represent the latest evidence of a gradual recalibration of President Bush’s position towards the issue.

For much of his presidency he has cast doubt on scientific evidence that mankind is responsible for global warming and even now he still rejects the imposition of greenhouse gas controls on US industry.

Dr Hays had led the US delegation to the Intergovernmental Panel on Climate Change and, it is alleged, watered down draft versions of yesterday’s report.

Other delegates said that a paragraph stating that North America was “expected to experience severe local economic damage and substantial ecosystem, social and cultural disruption” was removed at the behest of the US.

In a morning conference call, Dr Hays was asked whether she had made changes. “The US and many other nations were very much engaged in making sure that we took our role very seriously in getting a summary document that accurately reflects the underlying science . . . I think we helped craft a report that robustly reflects. . . this underlying, very long technical document,” she said.

Dr Hays suggested that “most impacts of climate change will be felt very regionally. . . some parts of the world are more vulnerable than others — for example, Africa, small islands, the Polar regions and so forth”. She said it was not true that “all projected impacts are negative” although she did concede that at “particularly higher potential future temperatures, the range of projected impacts becomes increasingly negative”.

Mr Connaughton, chairman of the White House Council on Environmental Quality, dismissed a question about the US’s refusal to ratify the Kyoto Protocol as a “gross mischarac-terisation” and claimed that Mr Bush’s pledge this year to cut US petrol consumption by 20 per cent over the next ten years was a “mandatory cap” on emissions. The US was in the vanguard, he said, of developing new technologies with “key countries like China and India to try to find low-carbon coal”.

He referred to possible positive outcomes from climate change on US agricultural yields but added: “On the negative side, the very real prospect of more coastal flooding is something of high concern.”