Top U.N. climate change official, Yvo de Boer, announced on Thursday that he is resigning, effective July 1, from the post that he held for almost four years, the Associated Press reports. De Boer said he was announcing his departure now so that U.N. Secretary General Ban Ki-moon had enough time to find a replacement before the next large climate summit in Mexico this fall. During his tenure, de Boer used frequent press encounters to raise the profile of climate issues and privately lobbied world leaders. The failure of last December's Copenhagen climate summit reportedly demoralized him, although de Boer said that he had been planning to switch jobs before the event. His next move is to global accounting firm KPMG, where he will consult on climate and sustainability issues.