A leaked copy of a document on climate change being drafted for the G8 summit suggests plans have been watered down.
G8 countries do not agree on the existence of global warming
A version of the communiqué leaked in May treated climate change as a fact and pledged money to energy projects.
In the new version the words "our world is warming" appear in square brackets, meaning at least one country disagrees, and all financial pledges have gone.
UK Chancellor Gordon Brown said the only version that mattered would be agreed next month at the G8 summit.
He told Sky News: "What actually matters is what the final communiqué actually says and you will not know what that says until the world leaders actually get together.
"I would've thought the communiqué that we are talking about will be very different from the final communiqué after people have their time at Gleneagles."
Labour's ex-environment minister Michael Meacher suggested the US government would not sign up to a document that mentioned global warming.
"Presumably it was taken out because of the Americans," he said.
The new text was "very disappointing", he added, saying it was "extraordinary" that doubt was being cast on the notion the world is getting hotter.
But a Department for the Environment, Food and Rural Affairs (Defra) spokesman insisted negotiations on the communiqué had not finished.
"We are all working hard to achieve the best possible outcome at Gleneagles but we are in intensive negotiations and so we cannot say exactly what the outcome will be.
"As in any negotiation, there are multiple versions of texts around. What is important to stress is that the only text that matters is the one we agree at Gleneagles."
The earlier version of the communiqué agreed to provide three or four pots of money for new energy projects.
It also proposed a carbon challenge competition to find ways of combating climate change but the new document contained none of that.
Instead, the latest draft talks more of "market-led" schemes and "dialogues" over energy efficiency, rather than actual policy moves by governments.
Conservative environment spokesman Oliver Letwin branded Britain's record on reducing carbon emissions "lamentable".
"I cannot see how the prime minister and [Environment Secretary] Margaret Beckett will succeed in putting climate change at the top of our G8 presidency if we cannot produce a timely plan for reducing emissions in the UK."
Lib Dem environment spokesman Norman Baker branded George W Bush the environment's "public enemy number one".
"Tony Blair has got no influence on Bush when it comes to climate change," he added.
"Of course we must secure an agreement with the Americans where we can. However, we must secure a target-based successor to Kyoto without the US watering it own."
Greenpeace executive director Stephen Tindale described Mr Bush as "an international menace" and said Mr Blair should "press on regardless".
And Catherine Pearce, of Friends of the Earth, described the latest draft as "disastrous".
"There is not agreement on the science of climate change. There is no real agreement and commitment in terms of what can be done to bring down emissions."
But she acknowledged that Mr Blair was "in a very difficult place with the US and the fact that they are not willing to move".