United Nations climate chief Yvo de Boer has resigned. He will step down in July to become an adviser at the consultancy group KPMG.
His resignation comes two months after a climate conference in Copenhagen failed to reach a binding deal to succeed the Kyoto Protocol.
Mr do Boer says Copenhagen did not provide a clear agreement in legal terms, but the political commitment and sense of direction toward a low-emissions world are overwhelming.
His departure takes effect from 1 July, five months before another attempt for a global deal, in Mexico.
Mr de Boer said he was announcing his departure now so that a successor could be found well before the Mexico meeting. The former Dutch civil servant had held the position since 2006.
The BBC reports suspicion and distrust between developing and industrial countries barred the way to a binding accord at climate conference in Copenhagen in December.