G-8 leaders meeting in Heiligendamm have agreed to "seriously consider" a 50 percent cut in global CO2 emissions by 2050, said Chancellor Angela Merkel, hailing the deal as a major success.

The summit had also agreed to negotiate a successor treaty to the Kyoto Protocol, which sets cuts in greenhouse gases running to 2012, within the framework of the United Nations, she said.

"It's a great success that we got this close to halving emissions," Merkel said in an interview on German television.

Merkel originally wanted the world's richest nations to commit themselves to lowering their CO2 emissions to 50 percent of their 1990 levels by 2050.

But US President George W. Bush resisted attempts to set a firm goal for cuts.

Merkel said G-8 environment ministers had been given a clear mandate to start negotiations about a Kyoto successor treaty at a UN conference in Bali at the end of the year.

She said there was "a clear commitment to continuing the UN climate process."

"The UN is the global institution in a global world, there was agreement on that," Merkel said.

One European Union official told Reuters that in the final G-8 text, leaders would acknowledge the desire of the European Union, Canada and Japan to cut emissions by at least 50 percent by 2050 -- in line with Merkel's stated target.