"We must have an agreement by the end of 2009, and then it will probably take about two years to reach a mandate," Sigmar Gabriel said, opening a two-day meeting of environment and energy ministers from 20 countries.

"If you think about how long it takes to reach an agreement just between the 16 German states ... you can see that it might take a while," he told the meeting called ahead of United Nations climate talks in Bali in December.

The meeting is designed to lay the groundwork for the new climate deal and aims to change the position of countries such as China and India who are wary of binding emissions cuts.

The Kyoto Protocol, which obliges 35 rich nations to cut greenhouse gas emissions, was agreed in 1997, but was not ratified until 2005, eight years later.

Many experts say 2009 is the latest practical date to agree a pact to succeed the Kyoto Protocol beyond 2012. Any firm building a coal-fired power plant or a wind farm needs to know rules for greenhouse gas emissions years in advance.

Gabriel criticised the "long-term aspirational goal" to reduce greenhouse gas emissions agreed by Asia-Pacific leaders at the APEC summit on Saturday.

"There's nothing in it that will mean much progress...it's far less ambitious than the agreement already reached by the European Union," he said.