British Prime Minister Tony Blair and German Chancellor Angela Merkel are urging US President George W Bush to agree to tough new international measures to stop global warming accelerating out of control.

The measures are contained in a strongly worded draft communiqué for June's G8 summit in Heiligendamm, Germany, which warns that "tackling climate change is an imperative, not a choice".

The draft warns that "global warming caused largely by human activities is accelerating" and that it "will seriously damage our common natural environment and severely weaken [the] global economy, with implications for international security".

It adds that if "resolute and concerted international action" is not "urgently" taken, global warming will become "largely unmanageable".

It says climate change has already progressed so far that the world will "have to face severe impacts" from it, even if immediate action is taken. But it adds that these will become largely unmanageable if the rise in temperature is not kept at 2C or below - the maximum increase that most scientists agree can be tolerated.

It promises "strong and early action" to hit this target, and says that this will involve cutting worldwide emissions of greenhouse gases in half by 2050. It commits developed countries to taking the lead, but adds that developing ones will also have to make "fair contributions" to the reduction. And it contains a lengthy section on how to reduce emissions through greater energy efficiency.

The United States is at present refusing to agree to any target for limiting global warming, and the issue will come to a head at a crucial preparatory meeting for the summit on 4 May.

Meanwhile, international relief agency Christian Aid recently joined forces with environmental broadband TV channel green.tv to recruit people to its new 'climate changed' campaign.

Three short films on the channel have been launched by the charity, which will appear in the climate change, technology and land sections of the site.

Working in 50 countries with 700 partner organisations, Christian Aid plans to upload more environmental films onto green.tv over the coming year. In particular it will be submitting films from its planned 1,000 mile 'Cut the carbon' march which begins in July and will be the UK's longest ever protest march.