The sharp-tongued U.N. official who shepherded troubled climate talks for nearly four years announced his resignation Thursday, leaving an uncertain path to a new treaty on global warming. Exhausted and frustrated by unrelenting bickering between rich and poor countries, Yvo de Boer said he will step down July 1 to work in business and academia.

With no obvious successor in sight, fears were voiced that whoever follows will be far less forceful than the skilled former civil servant from the Netherlands. His departure takes effect five months before 193 nations reconvene in Cancun, Mexico, for another attempt to reach a worldwide legal agreement on controlling greenhouse gas emissions, blamed for the gradual heating of the Earth that scientists predict will worsen weather-related disasters.

The resignation ''comes at the worst time in the climate change negotiations,'' said Agus Purnomo, Indonesia's special presidential assistant on climate change. ''His decision will ultimately add to the difficulties we already have in reaching a successful outcome in Mexico.''

De Boer made the announcement just two months after a disappointing summit in Copenhagen that ended with a nonbinding accord brokered by President Barack Obama promising emissions cuts and immediate financing for poor countries -- but even that failed to win consensus agreement.

In an AP interview last month, de Boer acknowledged that the summit left him deeply disheartened. ''After Copenhagen I was very depressed. I was depressed for a few weeks,'' he said.

But within days he was holding private talks to patch over bitter accusations between Britain and China, and was publicly calling on all sides to stop slinging mud about responsibility for Copenhagen's breakdown.

De Boer's successor will be named by Secretary General Ban Ki-moon, who has put climate change on the top of his own and the U.N.'s priorities. He is likely to look for a candidate from the developing countries.

The U.N. chief would customarily consult on the choice with the 11-member ''bureau,'' a rotating body of national delegates that deals with administrative issues and represents the major regions and negotiating blocs in the climate talks.

Among its members are several who are unlikely to want a strong-willed diplomat in de Boer's vacated chair.

They include the chief delegate from Sudan and spokesman for the developing countries, Lumumba Di-Aping, who rocked the Copenhagen conference when he accused wealthy countries of imposing a deal that would condemn the poor countries of Africa to a genocide comparable to the Holocaust. Another member of the bureau is Mohammad Salim al-Sabban, a counselor of Saudi Arabia's petroleum ministry.

Despite de Boer's frenetic diplomacy talks on a successor accord to the 1997 Kyoto Protocol, which set emissions targets for industrial countries, have been bogged down in mutual recriminations and arguments over sharing the burden of fighting climate change.

De Boer told The Associated Press he believed climate talks should be conducted differently, relying less on formal negotiations among thousands of delegates from nearly 200 countries and instead seeking agreement among smaller groups to lay the groundwork of a deal.

''At the moment, it tends to be very much a stop-and-start affair with everything concentrated in the formal negotiations, where I think a much more continuous engagement ... is needed,'' he said.

Though he said Copenhagen ''wasn't what I had hoped it would be,'' he said the frustration over the summit was not responsible for his decision to quit. Rather, it was time to seek new challenges. ''I took this job to see the launch of negotiations on a global response to climate change,'' he said in an interview. ''I feel that's happened. ... I think things are on track.''

De Boer won wide praise Thursday for raising the profile of climate change on the international agenda.

''I have always greatly appreciated Yvo de Boer; his engagement and his sharp tongue. Not always a perfect diplomat,'' said Connie Hedegaard, the European Union's commissioner for climate action.

Todd Stern, Obama's special climate envoy, praised de Boer as ''an enormously dedicated leader'' who made a major contribution to fighting climate change.

De Boer's job was not supposed to involve him directly in the negotiations, yet he lobbied, prodded, formulated tasks and goals, and frequently chided governments for moving too slowly and being too obstinate. He described his role as ''the conscience of the process.''

Often accused of overstepping the bounds of his office, he didn't disagree. ''They are absolutely right. I did that because I felt the process needed that extra push,'' he told the AP on Thursday.

He recalled that when he was picked for the job by Kofi Annan in 2006, he told the then-U.N. Secretary General: ''If you want someone to sit in Bonn and keep his mouth shut then I'm not the right person for the job.''

Asked about his greatest satisfaction, he said noted the plan adopted in 2007 in Bali, Indonesia, when developing countries agreed to join in efforts to contain global warming in return for financial and technical help from the wealthy nations.

The Bali meeting was so intense that during its final meeting, when he was accused of mishandling negotiating arrangements, he walked off the podium in tears. He came back later to an ovation from the thousands of delegates.

(AP, NYT, 18/02/2010)