The G8's plan for action to tackle climate change has been watered down in an attempt to pacify the White House, environmentalists claimed today.

A leaked communiqué of the text due to go before world leaders next month reveals that some of the central commitments have either been stripped out or enclosed in square brackets, indicating a failure to reach unanimous agreement in advance.

In addition, offers of new money for research into green technology have disappeared, and a reference has been included specifically endorsing further research into "zero-carbon" nuclear power.

Tony Blair has pledged to put climate change at the heart of Britain’s 12-month presidency of the G8 but, with less than three weeks to go before world leaders gather for the summit in Gleneagles, delegates are no longer being offered a clear and definitive statement that man-made global warming is happening.

Commentators today suggested that Mr Blair now faced a difficult choice: to dilute his personal ambitions for tackling climate change, or to weaken his ties with President Bush.

The key changes to the latest communiqué, which appear to undermine the very fabric of global environmental policy, include putting the following statements in square brackets, to show they are disputed:

"[Our world is warming]"

"[The problem is urgent]"

"[The increase is due in large part to human activity]"

"[The world's developed economies have a responsibility to show leadership]"

This draft differs significantly from an earlier draft leaked on May 2 - which was itself criticised for including no specific targets or timetables for action.

Environmentalists today claimed that the sweeping changes were made in order to ensure that the policy would be acceptable to the White House, which has refused to adopt the Kyoto Protocol.

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