Rajendra Pachauri, the head of the United Nations Intergovernmental Panel on Climate Change, resigned from his post Tuesday after an employee at his research firm accused him of sexual harassment.

Indian law enforcement officials are investigating the claims from a 29-year-old female employee of the Energy and Resources Institute, or TERI, in New Delhi. The allegations against Pachauri, 74, include claims that the influential climate change authority repeatedly sent suggestive text messages, e-mails, and WhatsApp messages to the researcher, the woman’s lawyers told the Guardian. Some of those alleged messages have been published in Indian media reports.

Pachauri denies the allegations against him. As the Guardian reported, Pachauri’s legal team has said that the messages in question were the result of a hack that aimed to ruin his reputation.

In his resignation letter to Secretary-General Ban Ki-moon, Pachauri said that he had planned on resigning last year after the release of a major report that warned of “irreversible” climatic disruption resulting from increasing amounts of greenhouse gasses. But, he wrote, “close friends and colleagues advised me against that action and to continue with outreach efforts worldwide based [on the report.].”

“The IPCC needs strong leadership and dedication of time and full attention by the Chair in the immediate future, which under the current circumstances I may be unable to provide,” Pachauri’s resignation letter continues, referring to his “inability to travel to Nairobi” to chair a key panel this week.

A spokesperson for the IPCC told the Associated Press earlier this week that Pachauri was unable to attend this week’s plenary session “because of issues demanding his attention in India.” Pachauri said in an earlier statement that he was “committed to provide all assistance and cooperation to the authorities in their ongoing investigations.”

The IPCC is considered to be a leading world authority on the science of climate change. The panel’s reports draw from contributions from thousands of international climate scientists.

Pachauri’s current term as IPCC chair was set to expire in October. Vice Chair Ismail El Gizouli will now serve as acting chair of the panel.

“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, said in a statement following Pachauri’s resignation. The UN’s Environment program is a sponsor of the IPCC.

Pachauri also pledged to continue outreach on climate change issues in “whatever capacity I work,” adding: “For me, the protection of Planet Earth, the survival of all species and sustainability of our ecosystems is more than a mission, it is my religion and my dharma.”

The Energy and Resources Institute told the BBC that Pachauri is currently on “leave.” An official at the think tank said Pachauri was still affiliated with TERI, the Wall Street Journal reported.

Pachauri had chaired the influential IPCC panel since 2002. In 2007, the organization won the Nobel Peace Prize alongside Al Gore for their “efforts to build up and disseminate greater knowledge about man-made climate change.” Pachauri delivered the Nobel lecture on behalf of the IPCC.

Five years ago, Pachauri faced a round of calls for his resignation after the IPCC admitted its 2007 climate change report contained a “poorly substantiated” claim that the Himalayan glaciers could melt as soon as 2035.

Around the same time, a report in the Telegraph raised questions about whether Pachauri was personally profiting from his influential role at the UN. At the time, Pachauri told the Guardian: “They can’t attack the science so they attack the chairman. But they won’t sink me. I am the unsinkable Molly Brown. In fact, I will float much higher.”

An independent review cleared Pachauri of any allegations of financial misconduct, and the Telegraph issued an apology for “any embarrassment caused” by its reporting, saying: “It was not intended to suggest that Dr. Pachauri was corrupt or abusing his position as head of the IPCC.”

[This post has been updated.]