US President Joe Biden is expected to sign many executive orders to reverse some of Donald Trump’s most controversial policies.
To begin his ground-breaking set of environmental policies, he will move to rejoin the 2015 Paris Climate Agreement.
What you need to know.
What is the Paris Climate Agreement?
Almost every country signed the Paris Agreement – 195 nations and the EU.
It was signed on December 12, 2015, after two weeks of wrangling at the Paris Conference of the Parties to the UN Framework Convention on Climate Change, or Cop21.
It is the first binding multilateral agreement on climate change and came into force in November 2016.
The accord sets a target of limiting warming of the planet to 2ºC above pre-Industrial Revolution levels, while aiming for an even more ambitious goal of 1.5ºC.
What did signatories promise?
Each nation that signed up committed to specific climate goals for their country, called nationally determined contributions.
The UK and Japan committed to net-zero carbon emissions by 2050.
There is also a system for developed countries, by far the worst polluters, to assist developing nations in mitigating the effects of climate change.
A new batch of national goals came into force at the end of 2020 and were supposed to stretch nations even further to cut carbon emissions.
But only 44 countries and the EU met this deadline and many of the contributions or targets stayed the same as in 2015 – some were even reduced.
There is no penalty for leaving the agreement but the US is the only nation to do so.
When did the US leave?
Donald Trump announced his intention to pull the US out of the agreement on June 1, 2017, saying it disadvantaged the US.
“The Paris Climate Accord is simply the latest example of Washington entering into an agreement that disadvantages the United States to the exclusive benefit of other countries, leaving American workers – who I love – and taxpayers to absorb the cost in terms of lost jobs, lower wages, shuttered factories and vastly diminished economic production,” he said at the time.
When the US signed the deal, it committed to cut climate pollution by between 26 per cent and 28 per cent from 2005 levels.
The decision to pull out by the world’s second-largest greenhouse gas emitter behind China was widely criticised.
Shortly after the US dropped out, Syria signed up, making the US the only country in the world that was not a signatory.
What else is Biden planning for the environment?
The journey back to setting an example on climate change is going to be an arduous one after four years of scientists being pilloried and environmental legislation withdrawn.
"We got off track very severely for the last four years with a climate denier in the Oval Office," John Podesta, an adviser to former president Barack Obama who helped to craft the 2015 Paris Agreement, told Reuters.
"We enter the international arena with a credibility deficit."
Nevertheless, Mr Biden and Vice President Kamala Harris have bold plans.
There will be a sweeping order to review all of Mr Trump's actions weakening climate change protection and the revocation of a vital permit for TC Energy's Keystone XL oil pipeline project from Canada.
There will also be a moratorium on oil and gas leasing in the Arctic National Wildlife Refuge, which Mr Trump's administration recently opened to development.