Just months after helping to piece together a global accord on climate change in Copenhagen, U.N. top climate official Yvo de Boer announced that he will be resigning from his position.

The 55-year-old Austrian made the unexpected announcement on Thursday, saying that he will step down on July 1 to pursue a career in the private sector and academia.

"It was a difficult decision to make, but I believe the time is ripe for me to take on a new challenge," De Boer said.

De Boer has worked for the past four years leading the U.N.'s efforts to cut global greenhouse emissions. His work culminated last December at the COP 15 conference in Copenhagen, where he presided over negotiations that led to the development of the Copenhagen Accord.

Colleagues of De Boer expressed regret at the announcement, including British climate official Ed Miliband who noted: "Yvo de Boer's patient work helped produce the Copenhagen Accord which contains commitments covering 80 percent of global emissions, something never previously achieved."

 "We must quickly find a suitable successor, who can oversee the negotiations and reform the UNFCCC to ensure it is up to the massive task of dealing with what are some of the most complex negotiations ever."

Others have seen de Boer's resignation as a sign of the U.N.'s weakening role in global climate talks, which are expected to be taken over by large emitting nations.

"It's a death knell for the U.N. process," Frank Maisano, a lobbyist on energy issues at Bracewell & Giuliani, told the Washington Post. "It's clear now that you're going to have to solve this issue through agreements with major emitters."

Meanwhile, major emitting nations have shown little progress towards achieving the comprehensive, legally binding climate agreement which was expected at Copenhagen.

Deadlocks in Congress have slowed President Obama's efforts to meet pledges for emissions cuts, while leaders in China have continued to show disinterest in meeting standards for international transparency and monitoring.

The lack of progress since Copenhagen has left many doubtful about whether a major agreement can be reached at the next international climate conference in Cancun later this year.

"It is becoming increasingly clear that a legally binding treaty is not in the cards for Cancun," Michael Levi, a senior fellow for energy and environment at the Council on Foreign Relations told the Washington Post.

"It's not that people have problems with the direction in which they're going. People aren't quite sure what direction they're going in at all."