UNITED NATIONS  The sense of disarray in the global effort to address climate change deepened Thursday with the resignation of Yvo de Boer, the stolid Dutch bureaucrat who led the international climate change negotiations over four tumultuous years.

His departure, which takes effect on July 1, comes after a largely unsuccessful meeting in Copenhagen in December that was supposed to produce a binding international treaty but instead generated mostly acrimony and a series of unenforceable pledges by nations to reduce their global warming emissions.

Mr. de Boer did not directly link his decision to step down to the chaos at Copenhagen. But he was known to be frustrated and exhausted by the meeting’s failures. His resignation was seen by some as a further sign that the United Nations framework, which for almost two decades has been viewed as the best approach to tackling global warming, may have outlived its usefulness. And it raised questions about whether any significant progress toward a global treaty would be made by December, when the next United Nations climate talks are to be held in Cancún, Mexico.

“If Yvo de Boer thought that there would be a legally binding treaty at the end of this year, I suspect he would be sticking around to take some of the credit for it,” said Michael A. Levi, an expert on climate change at the Council on Foreign Relations. “He has put in a lot of time toward a very well-defined end.”