Joe Biden. Photo: VCG

As Joe Biden leads the US back into the Paris Agreement on climate change, after taking office on Wednesday, diplomats and green groups will breathe a collective sigh of relief - before urging him to step up cuts to US emissions.

Soon after his inauguration, Biden was expected to issue an executive order to begin rejoining the 2015 climate pact, reversing a decision by climate-change skeptic former president Donald Trump.

The process to re-enter the international accord takes a month, meaning the US will only officially have been out of the deal for a short time since exiting in November.

But Trump's hostility to the UN climate process and his support for polluting fossil fuels have left Biden's team a lot of catching up to do at home and abroad, policy analysts said.

"Rejoining the Paris Agreement is really the floor, not the ceiling, for the Biden administration on climate," said Jennifer Morgan, CEO of Greenpeace International.

If the US government then moves to help drum up more global ambition to curb rising temperatures, it must be done in a spirit of "partnership and ­humility, not coming back in and telling everyone what they should be doing," Morgan said.

Rachel Cleetus, climate and energy policy director for the Union of Concerned Scientists, said there would be a number of opportunities in 2021 for Biden to help advance "a progressive climate agenda" on the world stage. Those include the G7 and G20 summits and the UN climate talks in November.

Biden and his international climate envoy John Kerry should also pursue meetings with other major emitters - as Biden has indicated he will do - "to solidify ways to collectively tackle the climate crisis head-on," she said.

One key task for Washington, after re-entering the Paris climate deal, will be to set a US emissions reduction target for 2030 and produce a stronger national climate action plan.

Signatories to the Paris accord were meant to submit updated plans to cut emissions and adapt to worsening extreme weather and rising seas by the end of 2020, but due to delays caused by the pandemic only about 70 have done so.