Updated with a federal judge ruling on April 19 that the Trump administration’s reversal of an Obama-era moratorium on coal leases was illegal.

Sen. Elizabeth Warren this week became the latest major presidential candidate to promise to halt all new leases for fossil fuel development on federal lands if elected. She said her moratorium would extend to new offshore oil and gas leases, and that she would pair those changes with initiatives to boost production of renewable energy.

A ban on new federal leases—also a central piece of Sen. Bernie Sanders’ climate platform in his bid for the presidency—would represent a major shift in federal policy. The Trump administration has pushed to unleash fossil fuel production with its “energy dominance” campaign, and even the Obama administration promoted some natural gas and oil drilling.

“Any serious effort to address climate change must include public lands,” Warren, a Massachusetts Democrat, wrote in announcing her proposal on Monday. She said she would implement it by executive order on her first day in office.

Her announcement comes as scientists and advocates are increasingly calling for urgent federal action to cut greenhouse gas emissions that fuel climate change, and as the Democratic candidates vying for the party’s nomination are trying to distinguish themselves on climate change and other issues.

Warren’s proposed moratorium would not change fossil fuel production overnight, though. 

Energy companies could continue producing under their existing federal leases for years. The Interior Department has said that current coal leases contain enough reserves to support 20 years of production. Oil and gas drillers are also sitting on 13 million acres that they’ve already leased but where they are not producing.

Federal lands account for about 40 percent of the nation’s coal production, a quarter of oil production and an eighth of gas output. The emissions from producing and using those fuels were equal to nearly 20 percent of the country’s total greenhouse gas output in 2014.

But while any reversal may take time to be felt, an analysis published last year by researchers at the Stockholm Environment Institute in Seattle estimated that a policy like the one Warren is proposing could, by 2030, cut global carbon dioxide emissions by 280 million tons per year, equal to pulling 54 million cars off the road.

Advocates say that leaving as much of the world’s fossil fuel reserves in the ground as possible is critical to meeting the goals of the Paris climate agreement to limit global warming to less than 2 degrees Celsius from pre-industrial times.

Trump Tried to Strip Away Earlier Leasing Limits

During the Obama administration, federal agencies began to include climate concerns in their reviews of energy projects.

That was part of why Obama rejected the Keystone XL oil pipeline from Canada’s tar sands, implemented a short-lived moratorium on new coal leasing on federal lands, and placed large parts of the Arctic and Atlantic oceans off limits to oil and gas drilling.

All of those policies were reversed by the Trump administration. President Donald Trump’s agencies have stripped away regulations meant to limit methane emissions from oil and gas drilling, opened up new areas in Alaska to drilling and proposed allowing drilling off nearly all of the nation’s coastline.

Some of the administration’s moves have been blocked by courts, however.

A federal judge in Montana ruled on April 19 that the Trump administration’s reversal of the coal lease moratorium was illegal because the Interior Department had failed to assess its environmental impact, as required under the National Environmental Policy Act (NEPA). U.S. District Court Judge Brian Morris ordered both sides in the case to work toward an agreement to present to the court on the current status of coal leasing, including leases affected by the moratorium.  

Last month, a federal judge in Alaska reinstated the Obama-era ban on drilling in parts of the Arctic and Atlantic oceans.

Domestic oil and gas production, which increased steadily during the Obama administration, has surged over the past two years. The United States is now the world’s top oil and gas producer, and an increasingly important exporter too.

Could Warren’s Plan Survive a Legal Challenge?

Several of the Democratic candidates for president have condemned Trump’s attempts to expand offshore drilling. Sen. Kirsten Gillibrand (D-N.Y.) joined Sanders and Warren in co-sponsoring a 2017 bill that would have halted the issuance of new fossil fuel leases on federal lands, similar to Warren’s new proposal. Rep. Tulsi Gabbard (D-Hawaii) sponsored a different 2017 bill to end federal permits for new fossil fuel projects.

While those moves could gain supporters, they also could generate stronger opposition in fossil fuel-producing regions.

Dan Naatz, a spokesman for the Independent Petroleum Association of America, issued a statement after Warren’s announcement this week saying that her proposal “would damage our economy and negatively impact job growth in communities across the United States.”

Michael Gerrard, faculty director at Columbia University’s Sabin Center for Climate Change Law, said in an email that a Warren administration would have to provide a clear rationale for implementing a ban on new leases, and pointed to the moratorium on coal leasing implemented by the Obama administration as precedent.

As long as her plan met a number of legal requirements, including providing an environmental assessment that justified the moratorium, he said, “it should survive attack in court.”

Climate Plan Also Boosts Renewable Energy

Warren, like many of the candidates, has said she supports the Green New Deal, which would shift the nation rapidly away from fossil fuels while promoting job growth and social justice. She sponsored a bill in the Senate last year that would have required companies to disclose more information about their climate risks and their emissions. On Monday, she also asked the Government Accountability Office to review the risks posed by climate change to defense contractors and the defense supply chain.

Her promise to halt new fossil fuel leasing could set a new benchmark for candidates as they roll out policy platforms in the 2020 campaign.

As part of her plan to boost renewable energy production on federal lands, Warren said she would set a goal of getting 10 percent of the nation’s electricity from renewable energy produced offshore or on federally owned land.

“We need our public lands and waters and the fossil fuels they hold to be part of the climate solution and not part of the problem, and that’s the direction her plan points in,” said Sharon Buccino, a senior adviser to the Natural Resources Defense Council Action Fund. “That doesn’t mean it’s an immediate halt to all drilling going on. But it does mean we’re not continuing to dig our climate hole deeper.”