Leaders of the world's most powerful countries, the G8, have agreed to limit the rise in global temperatures to no more than 2C.

Prime Minister Gordon Brown hailed the "historic" agreement between the world's major industrialised nations - Britain, the US, Germany, France, Italy, Canada, Japan and Russia - that will also see greenhouse gas emissions cut by 80 per cent by 2050.

Mr Brown said the deal, agreed at the G8 summit in the Italian town of L'Aquila - still reeling from April's devastating quake which killed 300 people - paved the way for a global agreement at the UN conference in Copenhagen in December to halve emissions by the middle of the century.

A communiqué released at the summit also committed the G8 to continued efforts to restore global economic growth, and put off the application of an "exit strategy" - as sought by Germany - until recovery is assured.

Mr Brown said the G8 leaders recognised "warning signals" that the path out of recession is not yet secured, citing the recent rise in oil prices to $75 a barrel and uncertainty about future unemployment.

Welcoming the agreement on climate change - made possible by America's change in stance since Barack Obama succeeded George Bush as President - Mr Brown said: "For the first time the G8 has agreed what I believe are vital decisions that take us on the road to Copenhagen and change the way we look at energy policy in the future."

He continued: "We have agreed for the first time that average global temperatures must rise by no more than 2C. That is a historic agreement. We have agreed as G8 that we want to cut our emissions by 80 per cent by 2050 and we believe that this will allow the world to reduce its emissions by 50 per cent."

The Prime Minister hopes to secure agreement from emerging economies including China and India on the need to limit temperature rises to 2C at a meeting on Thursday, but no deal is expected on specific emission cuts for non-G8 countries.

In L'Aquila, aftershocks measuring more than 4.0 have continued as recently as Friday, and the Italian organisers have put plans in place to evacuate leaders to Rome in the case of a serious tremor.

But officials have brushed off any suggestion of danger to the 20-plus heads of government, including President Obama, is attending.

Italian president Silvio Berlusconi, who is chairing the G8 this year, switched the summit venue from Sardinia to show solidarity with quake victims and has faced criticism for the supposedly chaotic preparation for the event, but UK officials insisted it had been "professionally run".

The meetings will be dominated by the global recession, with Britain seeking progress on the agreements reached at the G20 summit in London in April to reform the international financial system and pump billions into the world economy.

Ahead of the summit, Mr Brown said the international community must maintain its focus on restoring lending by banks, reining in oil prices - which have risen by 75 per cent this year - and fighting protectionism.

And Britain will hope to receive strong support in its current stand-off with Iran over a detained embassy worker, and leaders will also look at the prospects for nuclear weapons reductions following talks between Mr Obama and Russian President Dmitry Medvedev.

On Thursday, G8 nations will be joined by the "plus five" group of emerging economies China, India, Brazil, Mexico and South Africa to discuss climate change and development.

President Obama will chair the Major Economies Forum, comprising the world's biggest carbon emitters and also including Australia, Indonesia, South Korea and the EU, in a meeting designed to pave the way for a post-Kyoto agreement on action to halt global warming at Copenhagen in December.

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