LONDON - Climate campaigners said on Tuesday they expected a British government report on the global costs of climate change to make it clear that major concerted action was needed now.

The full report, an outline of which will be presented by former World Bank chief economist Nick Stern to a closed-door meeting of G8 environment ministers in Mexico later on Tuesday, is expected to be published later this month.

"The central message is that the problem is urgent, we have the technology to start addressing it now, we need to start addressing it now and there is no excuse for delay," Greenpeace climate change campaigner Steve Sawyer told Reuters.

Climate campaigners said Stern's outline report to the third follow-up meeting after the July 2005 G8 summit at Gleneagles in Scotland was expected to lay out a range of climate scenarios but leave the final choice of action to political leaders.

Despite a remark from British finance minister Gordon Brown last Monday that the report would be published within days, Stern's office has denied he will present the conclusions to the Monterey meeting or that a publication date has been set.

Campaigners based their assessments of the report's content on earlier drafts but have not seen the final version, which they say will make the case for urgent global action to mitigate and adapt to climate change.

At its core will be the need for the developed world to help rapidly industrializing nations like China and India develop low carbon economies and help offset the effects of global warming on poorer developing countries in Africa.

Stern's report was expected to outline a range of scenarios of what is likely to happen -- economically and socially -- at various levels of temperature increase, the campaigners said.

Scientists predict that average global temperatures will rise by between two and six degrees celsius (36 and 43 Fahrenheit) over the next century, driven mainly by so-called greenhouse gases like carbon dioxide from burning fossil fuels for power and transport.

"All of our work shows that once you go beyond two degrees warming we are moving from very nasty impacts into uncharted waters," WWF climate change chief Keith Allott said. "You enter into the area of dangerous feedback levels in the climate.

New research from WWF shows that at two degrees between 90 and 200 million more people are at risk from malaria, while over three degrees the figure shoots above 300 million.

Likewise, a two degree rise puts up to 50 million people at risk from rising sea levels due to melting ice caps, while at three degrees the figure surges to 180 million people.

There are similar step change increases in people at risk from increased hunger and disease.

"WWF is extremely hopeful that Sir Nicholas Stern will make a powerful case for urgent and concerted global action to avert dangerous climate change," Allott said.

Stern's presentation comes just days after PricewaterhouseCoopers issued a report stating that it will cost $1 trillion to curb emissions of climate warming gases over the next generation.