Eleven states and the District of Columbia sued the Trump administration on Wednesday, demanding enforcement of regulations on super-polluting greenhouse gases in air conditioners and refrigerators.

A similar lawsuit was filed by environmentalists on Tuesday. Both challenge an attempt by Environmental Protection Agency Administrator Scott Pruitt to roll back federal regulations on the class of chemicals known as hydrofluorocarbons, or HFCs.

The HFC lawsuits are the latest in a string of legal challenges to the Trump administration's far-reaching agenda of rolling back environmental regulations, especially those relating to climate change.

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Instead of launching a new formal rulemaking procedure to rescind or replace the HFCs rule, Pruitt announced in April that the agency would no longer enforce the Obama-era rule, which a federal court had partially struck down in a case brought by two foreign HFCs manufacturers.

The court had struck down only part of the HFCs rule, leaving some elements in place, yet Pruitt's move essentially eliminated the rule entirely. By using "guidance" to do that rather than going through the formal rulemaking process, Pruitt violated administrative law, the NRDC's Lissa Lynch wrote in a blog post explaining her group's lawsuit over the move.

"Throwing out these commonsense restrictions on this potent pollutant is contrary to the law and science, and it is disruptive to the manufacturers that have invested in alternatives," Massachusetts Attorney General Maura Healey said in announcing the states' lawsuit. "We are suing to protect the health of our residents and the planet."

An EPA spokesperson, asked about the lawsuits, said the agency does not comment on pending litigation.

Thousands of Times More Potent Than CO2

HFCs have become the world's fastest growing greenhouse gases as use of refrigeration and cooling spreads in a warming and more populous world. In the short term, they are thousands of times more potent as global warming gases than carbon dioxide, and while they don't last as long in the atmosphere, the short-lived climate pollutants have a rapid global impact.

The Obama administration finalized a rule in 2015 to phase out the chemicals. By then, U.S. manufacturers were already producing less damaging alternatives, and many companies supported the phase-down.

An analysis by Lawrence Berkeley National Laboratory estimated the rule would have provided about 4 percent of the cuts in greenhouse gas emissions the U.S. needed to meet its obligations under the Paris climate agreement.

What About the Kigali Amendment?

Another move to phase out HFCs has been developing at the international level, and the Trump administration at one point indicated it supported it.

In 2016, nations agreed to an update to the Montreal Protocol called the Kigali Amendment that requires all countries to slash production and consumption of HFCs by at least 80 percent over the next 30 years. It has the backing of a wide array of U.S. businesses, many of which manufacture safer alternatives to HFCs. But the Trump administration has yet to send it to the Senate for ratification.

Thirteen Republican senators, led by John Kennedy of Louisiana and Susan Collins of Maine, have urged the White House to move forward with the treaty, saying the amendment would help domestic companies by leveling the playing field worldwide and giving them long-term certainty on what chemicals to use going forward.

In the meantime, Pruitt's deregulatory moves, if they survive court challenges, would undercut U.S. progress toward meeting the Kigali goals.

Connections to an Ethics Scandal

HFCs have come up in the ethics allegations swirling around Pruitt, as well, the Washington Post reported this week. Emails obtained by the Sierra Club under the Freedom of Information Act show that J. Steven Hart, a lobbyist whose wife rented Pruitt a condo on Capitol Hill last year, had contacted Pruitt's chief of staff in 2017 seeking to discuss the HFCs rule and issues it might cause for companies. The agency has maintained that Hart did not lobby the agency on environmental issues. The matter is under investigation by both the EPA's inspector general and the House oversight committee.

The attorneys general who sued over HFCs represent New York, California, Delaware, Illinois, Minnesota, New Jersey, Oregon, Vermont, Washington and the District of Columbia, and they were joined by the Pennsylvania Department of Environmental Protection. Earlier this year, California regulators adopted their own state prohibition on HFCs in new air-conditioning and refrigeration.

"The Trump EPA is seeking to gut critical climate protection rules through the backdoor—once again endangering New Yorkers while thumbing their nose at the law," New York Attorney General Barbara Underwood said.