Host Japan called the summit a success, highlighting the G8's commitment to halve global greenhouse gas emissions by 2050.

But the size of the cuts was not quantified, since leaders did not agree on a base year with which to compare emission levels. Nor did leaders agree on any medium-term cuts, as many had hoped. Environmentalists and developing countries called the deal toothless.

"On climate change, this summit will be seen as a setback, particularly since there is no baseline for the emission cuts and no medium-term objectives," James Meers, an analyst at the Munk Centre, a Canadian think-tank that assesses the results of G8s, told the DPA news agency.

New attendees

The summit in Toyako, in Japan's northern island of Hokkaido, was the largest ever, with a total of 22 countries represented.

For the first time, at the request of US President George W Bush, G8 leaders also held an enlarged Meeting of Major Economies (MEM) with Australia, Brazil, China, India, Indonesia, Mexico, South Korea and South Africa.

During Wednesday's MEM meeting, both rich and developing nations committed themselves to "a long-term global goal for emission reductions."

But the presence of big developing countries also highlighted differences between them and G8 members on the best way to tackle emissions reduction. Both recognized that "deep cuts" were needed in order to combat climate change, they failed to agree on setting specific targets, saying only that the reduction in greenhouse gases should take place according to the means of each country.

And no mention of the G8's "50 by 50" target was made in the joint statement with developing countries, evidence that big polluters such as China and India were not yet willing to commit themselves to internationally agreed cuts.

The discussion on global warming now moves on to Poznan, Poland, where world leaders will take part in December in a conference of the United Nations Framework Convention on Climate Change ahead of a decisive summit in Copenhagen next year.

Japanese Prime Minister Yasuo Fukuda said that resolving the differences between the European Union, which had pushed for heavy cuts, and the United States, which resisted them, the G8 had "contributed to building momentum for the UN negotiations."

Africa aid

In Japan, G8 leaders had also come under intense pressure to stick to their pledge to increase aid to Africa and help meet the UN's Millennium Development Goals (MDGs). These include halving global hunger and getting every child into primary school by 2015.

G8 leaders set a five-year deadline to commit $60 billion in funding to help the continent fight disease.

While they also reaffirmed their wish to increase, by 2010, annual aid to Africa by $25 billion, pressure groups complained that the leaders had failed to spell out exactly how such commitments would be met.

"The outcome of the G8 summit is nothing but an exercise in escapism. It is non-committal on major issues confronting the majority of the world's poor people," said ActionAid, a pressure group.

Oxfam International said it hoped key decisions would now be made at a special food crisis summit held by the UN in New York in September.

Oil and food

The poor state of the global economy also featured high on the G8 agenda, with leaders warning that spiralling oil prices posed a serious threat to future growth.

"We have strong concerns about the sharp rise in oil prices, which poses risks to the global economy," they said in a statement.

They agreed to hold a special energy forum that should focus on energy efficiency and new technologies. They called for an increase in oil production and refining capacities and for the building of more nuclear power plants.

G8 leaders also expressed "serious concern" about the surge in food prices, saying they had "serious implications for the most vulnerable" while also adding to "global inflationary pressure."

The asked nations with sufficient food stocks to release some of them to help others cope with soaring prices.

Zimbabwe

G8 leaders also urged Iran to stop its nuclear program and issued a statement voicing "grave concern" about the violence-marred re-election in Zimbabwe last month of Robert Mugabe.

The summit "made it clear we would impose new sanctions against an illegitimate regime that has blood on its hands," British Prime Minister Gordon Brown said, rallying world support for UN sanctions on Harare.

However, due to Russian opposition, it was not entirely clear whether the G8 had reached a consensus on the imposition of any new sanctions.

Fukuda said the matter would be referred to the UN Security Council in New York.

"(We had) a lot of meetings on important subjects, and we accomplished a lot," said George W. Bush, who was attending his final G8 as president of the United States.

The G8 comprises the world's seven richest countries -- Britain, Canada, France, Germany, Italy, Japan and the United States -- plus Russia. They account for two-thirds of the world's gross domestic product.

But as the summit closed Wednesday, German Chancellor Angela Merkel said: "The G8 is no longer enough to solve many of the problems."

Next year's summit is due to be hosted by Italian Prime Minister Silvio Berlusconi in Sardinia.