The meeting is likely to be dominated by climate change, poverty in Africa as well as the dispute between Russia and the US over a proposed missile defence system in Europe.
Protesters gather
On Wednesday, once again massive protests upstaged the discussions.
Around 10,000 anti-capitalism activists gathered on Wednesday in an attempt to blockade routes to the summit.
Police said that water cannon were used "twice after demonstrators bombarded police with stones". Eight officers were injured during clashes near the town of Bad Doberan, Luedger Behrens, a police spokesman, said.
At least 15 protesters were detained, police said.
By late afternoon, all three roads leading into Heiligendamm had been blocked off by protesters and police in full riot gear lined the entrance to the town. German NDR public radio said the only way in was by boat or helicopter.
World leaders are separated from the thousands of demonstrators by a 12km fence topped with barbed wire. Several protesters were seen trying to cut through the barbed wire which police had laid near the fence.
Greenhouse gases
Merkel has been pushing for a 50 per cent reduction in greenhouse gas emissions by 2050 to curb a rise in temperatures that scientists say could cause more droughts, heatwaves, floods and rising seas.
"The accelerated climate change is a serious threat," Merkel wrote in Der Tagesspiegel newspaper.
 |
Merkel, right, has been pushing for an
agreement on emissions targets [AFP] |
"If we don't stop it, it will lead to massive environmental problems and increased economic burdens.
Therefore, we need decisive action from the international community.
"In Heiligendamm we want to give impetus to the negotiations on global climate protection."
But Connaughton, who is chairman of the White House Council on Environmental Quality, said that the US would not agree until the issue had been discussed with other major emitting countries.
He said: "Until we've got everyone in the room and until we have consensus among all of them, you won't see a collectively stated goal on that. But it's coming."
Emerging nations
Merkel said helping the poor and developing African economies were other priorities of the three days of talks to which the leaders of emerging nations including South Africa are also invited.
She said she wanted the meeting to "give globalisation a human face" and hoped that the protests against the summit would be peaceful.
Haru Mutasa, Al Jazeera's Africa correspondent, said there was not much confidence among African organisations that anything would come out of the summit.
"They say they are tired of empty promises, they want something else done but they are concerned that issues might not be addressed at this summit," Mutasa said.
At last year's summit, the G8 pledged to offer 100 per cent debt relief and increase aid to poor countries by $50bn a year by 2010.
Half of that money is earmarked for Africa, but monitor groups and non-governmental organisations are concerned that the pledges are not being honoured.