But a joint statement released after Tuesday's discussions was loosely worded, following wrangling between European and Japanese officials over the issue.

"Summit leaders are united in the view that a long-term goal for reducing global GHG (greenhouse gas) emission by half or more by the year 2050 needs to be established," the statement said. It did not give a base year for the reduction in emissions to be calculated.

The statement also called on developing countries to make a fair contribution to the effort and said discussions for a post-2012 agreement should be completed as soon as possible, but did not set a date.

The Kyoto Protocol, which set targets for emission cuts for participating countries to be reached between 2008-2012, was rejected by the United States because it set no binding targets for developing countries such as China and India.

Merkel wants G8 leaders to agree to the 50 percent target at the German-hosted summit, but faces dissent from leaders including US President George W. Bush, who last week launched his own initiative calling for the top 15 greenhouse gas emitters to discuss the issue.

The EU's environment chief dismissed that plan as unambitious.