"I think that it is possible that we'll leave the summit with a commitment on the part of everyone to a substantial reduction of greenhouse gases by 2050 as a global target that is of the order of the type of figures the Europeans are talking about," said Blair, taking part in a last summit meeting with his friend U.S. President George W. Bush,
But agreement on the goal of a deep, fixed reduction of 50 percent was unlikely, he said.
"What is important is that that there should be a such a target and that is the sort of ballpark we're talking about," he said.
A gap remains between German Chancellor Angela Merkel's insistence on binding reductions and Bush's plan. Bush has proposed having the 15 top polluters meet and set a long-term goal, but decide themselves how much to do towards it.
Bush praised Blair, his ally in more than six years in office, saying he was "nostalgic" as they stood together for the last time at an international summit. Blair is leaving office June 27.
"This is the last meeting I will have with him as prime minister," Bush said. "I'm sad about that."
Said Blair: "To be absolutely frank at the moment ... I haven't had time to be nostalgic."
Blair and Bush then sat down for the first joint working session of the G-8, which will tackle tough issues including global warming, edgy relations with Russia and Moscow's opposition to Western efforts to secure independence for Serbia's Kosovo province.
Their host, Merkel, chaired the meeting, with Blair to her left and Bush next to him. Also at the table: Russia's Vladimir Putin, Italy's Romano Prodi, Canada's Stephen Harper, France's Nicolas Sarkozy, Japan's Shinzo Abe and Jose Manuel Barroso of the European Commission.