U.N. climate chief Yvo de Boer will step down to join a consultancy group as an adviser, he said on Thursday, two months after a Copenhagen summit failed to support a legally binding climate pact.

His decision is not expected to further derail U.N.-led climate talks to agree a successor to the Kyoto Protocol, divided over sharing the cost of cutting carbon emissions.

De Boer will leave on July 1 to join KPMG, the Secretariat for the U.N. framework convention on climate change (UNFCCC) said in a statement. He had led the agency since 2006 and his contract was expected to be extended in September.

It was a difficult decision to make, but I believe the time is ripe for me to take on a new challenge, working on climate and sustainability with the private sector and academia, de Boer said in the statement.

U.N. Secretary-General Ban Ki-moon will make the final decision on a replacement, a U.N. spokesman said.

Copenhagen did not provide us with a clear agreement in legal terms, but the political commitment and sense of direction toward a low-emissions world are overwhelming. This calls for new partnerships with the business sector and I now have the chance to help make this happen, de Boer said.

In advance of the December summit in Denmark, de Boer had said anything less than agreement on emissions caps for individual developed nations would count as failure.

De Boer, born in 1954, was a senior Dutch environmental official who has been far more outspoken than previous heads of the Bonn-based Secretariat. He had often criticized developed nations for what he called a lack of ambition in setting out cuts in greenhouse gas emissions by 2020.

But he also told developing nations not to get their hopes up too high. In the run-up to Copenhagen, he told African nations and small island states that their calls for deep cuts by the developed world represented too heavy a lift.

At a marathon U.N. meeting in Bali in 2007, de Boer left the room in tears after a Chinese delegate criticized the Secretariat for starting a key meeting before all delegates were present.

It wasn't that surprising ... I would like to see someone from a developing country who can negotiate with those countries, said Seb Walhain, head of environmental markets at Fortis Netherlands, of de Boer's departure.

Carbon markets depend on the U.N. talks and a Kyoto successor after 2012 to continue global trade in carbon offsets. It won't have any effect on the carbon market, said Walhain.

(Reporting by Michael Szabo and Gerard Wynn; Additional reporting by Alister Doyle in Oslo and Nina Chestney in London; Editing by Janet Lawrence)