India's Rajendra Pachauri quit as chair of the U.N. panel of climate scientists on Tuesday, ending 13 turbulent years in charge of the Nobel Peace Prize-winning group, after a sexual harassment complaint against him.
Pachauri, 74, has denied the allegation.
Chairman of the Intergovernmental Panel on Climate Change (IPCC) since 2002, Pachauri pulled out of an IPCC meeting in Kenya this week after Indian police started investigating the complaint by a female researcher in India.
Pachauri, whose second term as IPCC chair had been due to end in October 2015, has also suffered cardiac problems.
In a letter to U.N. Secretary-General Ban Ki-moon, he wrote that his inability to travel to Kenya showed he may be unable to ensure the "strong leadership and dedication of time and full attention by the chair" needed by the panel.
"I have, therefore, taken the decision to step down," he wrote. His Indian think-tank, The Energy and Resources Institute, also said on Tuesday that he had gone on leave.
Forceful in explaining climate science, he has been a repeated target of those who doubt global warming is man-made. Pachauri collected the Nobel Peace Prize in 2007 when the IPCC shared the award with former U.S. Vice President Al Gore.
Findings by the IPCC are the main guide for action by almost 200 governments which aim to agree a U.N. deal to limit climate change at a Paris summit in December. The panel completed a set of mammoth reports last year, the first since 2007.
The IPCC appointed vice-chair Ismail El Gizouli as acting chair and promised business as usual.
"The actions taken today will ensure that the IPCC's mission to assess climate change continues without interruption," Achim Steiner, Executive Director of the United Nations Environment Program, which oversees the IPCC, said in a statement.
Pachauri said he had considered stepping down last year after finishing the IPCC reports, which raised the probability that climate change is mainly man-made to at least 95 percent from 90 percent in 2007. Last year was the warmest on record.
He rejected calls to quit after an error in the 2007 report exaggerated the rate of melt of Himalayan glaciers. An external review at the time recommended that IPCC chairs should only serve one seven-year term.
"At this stage of the IPCC cycle this is probably manageable ... It's not an existential threat," said Jim Skea, a senior IPCC scientist who works at Imperial College in London.
He noted that governments approved a negotiating text for Paris this month based on IPCC findings, and that the IPCC had been due to pick a new chair before Paris.
"It's not ideal but he was close to the end of his term," said Bob Ward, of the Grantham Research Institute at the London School of Economics.
Candidates to succeed Pachauri include Jean-Pascal van Ypersele of Belgium, another IPCC vice-chair. If elected: "I would keep robust and independent science at the core" of the IPCC, he said on Twitter this week.
(Reporting by Alister Doyle in Oslo and Aditya Kalra in New Delhi; Editing by Janet Lawrence)