Prime Minister Tony Blair has hailed a G8 deal on climate change as "a major, major step forward" amid disappointment among environmental and anti-poverty campaigners.
At his last summit before leaving Number 10, Mr Blair said the agreement for a substantial reduction in greenhouse gas emissions - with a view to halving them by 2050 - would have been unimaginable a few years ago.
Leaders of the G8 nations - the US, Canada, the UK, France, Germany, Italy, Russia and Japan - agreed at their summit in Heiligendamm, Germany, that emissions should stop rising "followed by substantial global emissions reductions".
But the agreement was dismissed by Greenpeace as "barely worth the paper it's written on".
Mr Blair said: "The important thing is we now have an agreement, one: that we need a new worldwide agreement on climate change," he said. "Two: that at the heart of that should be a substantial reduction in greenhouse gas emissions. Three: in the process that will then work out what that cut in emissions should be there will be serious consideration given specifically to the goal of halving emissions by 2050.
"This is an agreement in which we want all the major countries to be involved, including America, China, India and others - the developed and the developing world." He said: "This is a major, major step forward."
US President George Bush has always made plain that America would only be part of a deal if it included nations such as China and India.
Asked if he was disappointed there was no commitment to halve emissions, only serious consideration, Mr Blair replied: "What you have got is a sense that a substantial cut in emissions is of the order of a halving of emissions."
Greenpeace UK director John Sauven said: "An agreement without targets is barely worth the paper it's written on. This document acknowledges the seriousness of the situation, then ducks reality by offering weasel words like `seriously considering', as if this was an after-dinner discussion rather than the most important issue facing the world."
Oxfam senior policy adviser Antonio Hill welcomed the fact that "the poorest countries, who are most affected by climate change, will have a seat at the table where solutions are discussed. However, it is profoundly disappointing that some members, including the world's leading polluter, the US, have failed to sign up to specific targets or even an indicative global stabilisation goal."
He said: "The eight most powerful countries in the world had an unprecedented opportunity this week to boost global efforts to respond to the threat of global warming and sharply reduce the risks that poor people face. They have taken one step forward, but they should be running by now."
* Today, Mr Blair will speak with Russian President Vladimir Putin about extraditing ex-KGB agent Andrei Lugovoy to the UK to face a charge of murdering Alexander Litvinenko.