The Group of Eight industrialised economies, including the United States, have agreed for the first time that they must limit worldwide temperature rises to 2degrees, but failed to reach agreement with developing nations on how that should be achieved a disappointment to those expecting US President Barack Obama to break a decade-long deadlock.
The G8, representing the richest nations, also agreed for the first time that it should collectively cut emissions by 80 per cent by 2050, and that the world should be able to cut its emissions by 50 per cent by the same date.
In a fudge designed to recognise the difficulties rich countries will face in meeting this target, the agreed G8 communique issued at the summit in L'Aquila, in Italy, set a fuzzy baseline for their 80 per cent cut ''of 1990 or later years''.
The communique also acknowledges baselines may vary but ''efforts must be comparable''.
United Nations scientists have used 1990 as the starting point, but the US and Japan have been using 2005 levels.
A cap on global warming of 2degrees is seen as the minimum to prevent irreversible global warming. There had been hopes in the run-up to the summit that the developing countries and the G8 would strike an agreement that worldwide emissions should be cut by 50 per cent by 2050, but developing nations held out.
These countries, led by China, India and Brazil, said they wanted to see more specific targets from the rich nations before they would make any commitments.
In addition, they wanted the rich countries to put out a specific figure on how much cash they were willing to pay to help with green technology transfers.
Mr Obama has so far resisted interim 2020 targets as he faces the more immediate task of passing cap-and-trade legislation through Congress quickly.
Nevertheless, the British Prime Minister, Gordon Brown, hailed the deal as ''historic agreements in terms of desired outcomes in climate change''.
Mr Obama will still chair a meeting of 17 nations, at which he will try to get a collective agreement to limit temperature rises to 2degrees on pre-industrial levels. Mr Brown insisted such an outcome would represent ''real progress''.
Green groups such as WWF and Oxfam argued the 2degree aspiration was severely weakened by the lack of interim targets on how it should be achieved.
The WWF Global Climate Initiative leader, Kim Cartensen, said, ''If they don't outline a path to reach an announced goal, the 2degree statement will just join a long list of broken promises.
'' An ambitious mid-term target for 2020 of developed countries is needed to ensure immediate action.''
British officials argue there is still time to hammer out a deal before the UN-sponsored Copenhagen summit called to set a worldwide framework to cut carbon emissions after 2012.
Mr Brown said, ''Today we have laid the foundations for a Copenhagen deal that is ambitious, fair and effective ... The world has now agreed that the scientific evidence is compelling and the G8 countries have agreed that developed countries will reduce carbon emissions by 80 per cent by 2050.''
But the clock is now ticking fast as the developed countries have yet to agree on their respective responsibilities. Guardian