US climate envoy John Kerry, a key player in the Biden administration's push to tackle climate change, will step down to work on the president's reelection bid, media reported Saturday.

The former secretary of state and senator has spent the last three years liaising with other countries to up commitments on climate change, including at the most recent COP28 UN climate summit in Dubai.

Kerry, 80, intends to help Joe Biden's campaign by publicizing the president's work in combatting global warming, according to multiple US media outlets citing officials familiar with the situation.

Kerry informed Biden of his intentions to leave on Wednesday, and his staff learned of the decision on Saturday, those officials said.

Apart from leading the US delegation at three UN climate summits, Kerry worked effectively with China despite complicated diplomatic relations. Together, the countries are the world's two largest polluters, accounting for 41 percent of greenhouse gas emissions.

In a rare display of unity, the United States and China helped carry the COP28 December climate summit in Dubai, where negotiators sealed a historic although watered-down agreement to begin to transition away from oil, gas and coal.

Kerry had welcomed his Chinese counterpart Xie Zhenhua a month earlier in California, where the two countries agreed on outlines of climate action that partly served as a basis for the nearly 200-nation Dubai deal.

News of Kerry's stepping down comes one day after Xie retired on health grounds.

One of Biden's first moves in office after his inauguration on January 20, 2021 was to rejoin the Paris climate agreement, which former president Donald Trump had exited.

Under the 2015 UN deal countries committed to limiting the Earth's warming to "well below" 2 degrees Celsius and preferably to the safer 1.5C threshold.

That said, the year of 2023 was the hottest on record, with the increase in Earth's surface temperature nearly crossing the critical 1.5C threshold, according to EU climate monitors.

Kerry, himself a onetime Democratic presidential nominee, will step down sometime in the coming months, according to Axios, which first reported the news.

The White House and Kerry's office did not immediately respond to a request for comment from AFP.