New US President Joe Biden will announce America’s return to the Paris agreement to fight climate change on Wednesday, which is the centerpiece of a number of day-one executive orders aimed at restoring US leadership in combatting global warming.

The announcements will also include a sweeping order to review all of ex-President Donald Trump’s actions weakening climate change protections, the revocation of a vital permit for the Keystone XL oil pipeline project from Canada, and a moratorium on oil and gas leasing activities in the Alaska National Wildlife Refuge that Trump’s administration had recently opened to development, Biden aides told US news outlets.

The orders mark the start of a major policy reversal in the world’s second-largest greenhouse gas emitter behind China, after four years during which Trump’s administration pilloried climate science and rolled back environmental regulation to maximize fossil fuel development.

Biden has promised to put the United States on a track to net-zero emissions by 2050 to match the steep global cuts that scientists say are needed to avoid the most devastating impacts of global warming, using curbs on fossil fuels and massive investments in clean energy.

Within a week, Biden will take even more sweeping action, according to a document obtained by The Washington Post. He plans to sign a sweeping executive order elevating climate in domestic and national security policy; directing science and evidence-based decision-making in federal agencies; reestablishing the Presidential Council of Advisors on Science and Technology, and announcing US data that will help underpin the Climate Leaders’ Summit that Biden will host in Washington in late April.

Though incoming presidents frequently sign executive orders on their first day, the chasm between Biden’s agenda and Trump’s legacy is one of the widest in recent decades. Nowhere is that contrast more pronounced than on climate change ­­– which Trump largely dismissed altogether – and the environment, where Trump and his deputies scaled back a range of protections to benefit the fossil fuel industry.

But the path won’t be easy, with political divisions in the United States, opposition from fossil fuel companies, a global pandemic, and wary international partners concerned about US policy shifts standing in the way.

“We know rejoining [Paris] won’t be enough, but along with strong domestic action, which this executive order kicks off, it is going to be an important step for the United States to regain and strengthen its leadership opportunities,” Gina McCarthy, Biden’s national climate adviser told reporters late Tuesday.

The process of rejoining the Paris Agreement will begin today with a letter to the United Nations requesting U.S. membership. It will take 30 days for the US to formally reenter the nonbinding global agreement to reduce emissions.

Other orders Biden will sign on the first day instruct the Environmental Protection Agency and Transportation Department to strengthen fuel efficiency standards for cars and light trucks, which Trump weakened. He also asked two other departments, Interior and Commerce, to review the boundaries and protections Trump had scaled back for the Grand Staircase-Escalante and Bears Ears national monuments in Utah, and the Northeast Canyons and Seamounts Marine National Monument off the coast of New England.

The Wednesday orders also revive an interagency working group that Trump disbanded in 2017, which sets the social cost of carbon by estimating the economic damage caused by the release of a ton of carbon dioxide into the atmosphere.

Policymakers factor this figure into the costs and benefit calculations they make on a host of issues, from permitting a new oil well to imposing stricter pollution controls on coal- and gas-fired power plants. Under the Obama administration’s formula, the price per ton would now stand at $52, but Trump officials reduced that to between $1 and $7 per ton, the Washington Post reported.

Global counterparts and climate advocates welcomed Washington’s return to cooperation on climate change, but expressed some skepticism about its staying power, and its ability to overcome domestic political turmoil to enact ambitious new regulation.

“The United States continues to be the one and only country that has withdrawn from the Paris Agreement, making it, frankly, the pariah of this multilateral agreement,” former U.N. climate chief Christiana Figueres, told Reuters.

Hua Chunying, a spokeswoman for China’s foreign ministry, told the agency that China, the world’s top carbon emitter, “looks forward” to the return of the United States to the Paris pact.