A United Nations report published Wednesday highlights the legal risks that opponents say President Donald Trump faces if he does not withdraw from Paris climate agreement.

The Paris Agreement could be used to force governments, including the Trump administration, “that have adopted climate-oriented laws to implement them,” reads the UN Environmental Program report on global warming litigation.

The report claims that litigation “has arguably never been a more important tool to push policymakers and market participants” to fight global warming.

President Donald Trump promised to “cancel” the Paris Agreement on the campaign trail, but his White House is split on the issue. Opponents of the Paris Agreement argue that failure to withdraw could give environmentalists a legal avenue to keep Obama-era global warming policies in place.

“‘Crucial legal predicate for pushing governments is code for the hook that activist green groups, attorneys general and courts are looking for,” Chris Horner, a senior fellow at the Competitive Enterprise Institute (CEI), told The Daily Caller News Foundation.

The UNEP report notes that while Paris does not impose legally-binding requirements for countries to cut greenhouse gas emissions, it “enables litigants to construe governments’ commitments and actions as being adequate or inadequate.”

“The key question, which this cryptically addresses, is the legal risk that results from staying in Paris,” Horner said.

“I understand that has been internally conceded even by the State Department legal advocates,” Horner said, noting that a recent State Department memo did not include these doubts.

“The Paris Agreement by its own terms does not provide litigants with a cause of action or impose enforceable limits on member countries’ national emissions,” reads the UNEP report. “But it makes it possible for litigants to place the actions of their governments or private entities into an international climate change policy context.”

“Ultimately, while the Paris Agreement does not assign each country a carbon budget, it does offer a basis for deducing a budget from national commitments. It also makes clear that policies leading to net increases in emissions are disfavored,” the UNEP reports.

Hundreds of climate-related lawsuits have been filed in national courts, mostly in the U.S., to compel governments to impose more regulations, assign damages to emitters and stop projects that could increase emissions.

For example, Dutch activists sued the Netherlands in 2015 for not doing enough to fight global warming. The court sided with activists and “ordered the Dutch state to limit GHG emissions to 25 percent below 1990 levels by 2020,” according to the UNEP. That was before the Paris Agreement was passed.

The UNEP said Paris is “emerging as a novel and unique anchorage for lawsuits of this sort.”

Swiss environmentalists filed a petition in 2016 making arguments similar to Dutch activists, but this time the buttressed their claims with the Paris Agreement. Austrian activists used the Paris Agreement to argue against expanding the Vienna airport.

Norwegian campaigners used the Paris Agreement to bolster their legal challenge lease sales to explore for offshore oil and sell a coal mine instead of decommissioning it. Swedish activists challenged the sale of coal mines and plants in Germany under the Paris Agreement.

Horner pointed to a memo he obtained that New York Attorney General Eric Schneiderman circulated with fellow Democratic AGs in 2016 to “ensur[e] that the promises made in Paris become reality.”

The Paris debate has divided the Trump administration.

White House chief strategist Steve Bannon and EPA Administrator Scott Pruitt support withdrawing from Paris. Ivanka Trump, her husband Jared Kushner, Secretary of State Rex Tillerson and Energy Secretary Rick Perry support remaining in Paris.

Some Republicans have also championed staying in the Paris Agreement, but weakening the commitments made by President Barack Obama to cut U.S. greenhouse gas emissions 26 to 28 percent below 2005 levels by 2025. Pro-Paris Republicans want to weaken this and subsidize clean coal technology.

Whether or not the U.S. can weaken the Obama administration’s pledge is hotly debated by both sides of the issue. Former State Department Deputy Legal Adviser Susan Biniaz, who helped write the Paris Agreement, said the U.S. could weaken its pledge.

“In sum, while a downward revision is liable to draw criticism, it is a legally available option under the Paris Agreement,” Biniaz wrote in a memo for the Center for Climate and Energy Solutions.

Biniaz argued that courts were unlikely to go along with environmentalist legal lawsuits trying to prevent Trump from rescinding an Obama-era regulation. The Sierra Club also came to a similar conclusion.

She wrote that, “Courts would almost certainly find that the agreement does not constrain executive branch action.”

“Nothing either in the Paris Agreement itself or in its adoption by the United States suggests that it was intended to be self-executing,” Biniaz wrote.

The UNEP report notes the Paris Agreement “does expressly call on national governments to make their mitigation commitments incrementally more stringent and never less so.”

“Thus, even if a national government can argue that it never specified a level of emissions reduction it cannot argue that its commitments permit backsliding,” the report concluded.

Trump is expected to make a decision on whether or not the U.S. will stay in the Paris Agreement after he returns from his trip to Europe.

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