NAIROBI (AFP) - The head of the UN's climate science panel, Rajendra Pachauri, has stepped down, the organisation announced on Tuesday, amid claims that he sexually harassed a subordinate.

"The bureau of the Intergovernmental Panel on Climate Change agreed on Tuesday... to designate vice-chair Ismail El Gizouli as acting IPCC chair," it said.

"The designation of Gizouli follows the decision by Rajendra K Pachauri, PhD, to step down as chairman of the IPCC effective today."

Pachauri's second consecutive six-year term as IPCC chairman had been due to end in October, just weeks before the Paris conference.

The industrial engineer-turned head of the IPCC and one-off sex novel author is no stranger to accolades - nor to controversy.

At his peak, the now 74-year-old Indian accepted the Nobel Peace Prize on behalf of the policy-shaping body he heads, and was showered with national honours and honorary doctorates.

He is now alleged to have sexually harassed a 29-year-old woman researcher from the Energy and Resources Institute (TERI), the Delhi think-tank he heads.

The allegations had forced the bearded father-of-three, who denies any wrongdoing, to pull out of a four-day conference at a highly sensitive time, with the global community preparing to ink a planet rescue pact in December. That deal will be largely informed by the IPCC's Fifth Assessment Report, a summary of the latest climate science.

It warns that on current greenhouse gas-emission trends the world is on track for double the UN goal of limiting global warming to 2 degrees Celsius (3.6 degrees Fahrenheit), resulting in devastating floods, droughts and rises in sea level.

Pachauri, a vocal advocate of tough action against global warming, has had many career ups and downs, and this is not the first time he has faced public scrutiny.

He had to weather calls for his resignation after gross errors were found in a landmark IPCC report, and faced widespread ridicule for an attempt at erotic literature.

In 2007 he held aloft the Nobel jointly awarded to the IPCC under his chairmanship, and to former US vice president-turned climate campaigner Al Gore.

But three years later Pachauri was mired in controversy when errors were found in the IPCC's Fourth Assessment Report. An erroneous claim that Himalayan glaciers could be lost by 2035 was allegedly taken from a press article instead of a scientific study.

Pachauri refused to accept personal responsibility for the error and rejected pressure to step down, claiming "ideologically-driven posturing" was behind attacks on the IPCC.

LITERARY FORAY

An international review at the time called for fundamental reforms at the IPCC, including an overhaul of the post of chairman which Pachauri first took up in 2002.

Some critics have questioned where his loyalties lay, given his business dealings with carbon trading companies. According to a CV on the TERI website, Pachauri had during his IPCC tenure also served on the boards of India's Oil and Natural Gas Corporation and natural gas company GAIL.

Educated in Britain and the United States, where he earned doctorates in industrial engineering and economics, Pachauri is a sustainable development veteran. But his critics, who once included Gore, stress that he has no science qualifications.

An avid cricket fan and vegetarian, Pachauri has said his focus on the health of our planet came from his childhood in India's Himalayan foothills - not far from some of the glaciers that have since blemished his career.

"It was so beautiful and unpolluted when I was a child," he told AFP in 2007. "One saw the beauty of nature at its most pristine. It gets into your soul and you don't lose that."

Having penned more than 130 academic papers and nearly 27 books, mainly related to energy and the environment, Pachauri generated warming of a different kind when he tried his hand at creative writing with the 2010 novel "Return to Almora".

The offering is laced with steamy references to the sexual urges of protagonist Sanjay Nath who, like Pachauri, studied engineering.

He has hinted that the book, which interweaves themes of reincarnation with breathless accounts of Nath's carnal prowess, may be based on his own life.

His very appointment was controversial. Pachauri was regarded as a compromise candidate to replace the outspoken British-American scientist Bob Watson whom sources claimed was forced out by the climate-sceptic Bush administration.