The U.S. Environmental Protection Agency on Tuesday announced it plans to walk back a declaration in the Clean Air Act that determined greenhouse gases endanger public health and welfare.

The U.S. EPA declined CBS News Chicago’s request for an interview. But the Illinois EPA said it reviewing the proposal to rescind the declaration issued back in 2009 under President Barack Obama.

Meanwhile, climate experts in Illinois and around the country are concerned about the ramifications.

Lee Zeldin, President Trump’s pick to head the U.S. EPA, announced Tuesday from an Indiana auto dealership that the agency wants to repeal the 2009 Endangerment Finding.

“If finalized, today’s announcement would amount to the largest deregulatory action in the history of the United States,” Zeldin said, “a proposal to eliminate to the endangerment finding, to eliminate greenhouse gas standards — all the regulations that came out, including the electric vehicle mandates, all of the greenhouse gas standards for light-, medium- and heavy-duty.”

The 2009 finding that Zeldin is proposing eliminating determined that six specific greenhouse gases — carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆) — endangered public health and welfare. The finding set the platform for actions to regulate greenhouse gas emissions and fight climate change.

“it’s the fundamental linchpin of the Clean Air Act,” said Howard Learner, chief executive officer and executive director of the Environmental Law and Policy Center.

Learner called the U.S. EPA proposal a denial of both climate change and “fact-based determinations” about greenhouse gases.

“Climate change is real. It’s happening,” he said. “That can’t be denied as a basis of scientific fact.”

Learner said the impact in the Chicago area and elsewhere in Illinois would be dirtier air and more contributions to climate change.

“It’s showing up in our weather. It’s showing up in health risks. It’s showing up in the Great Lakes. It’s showing up in ways that change our lives here in Chicago and across Illinois,” Learner said.

In a news release, the U.S. EPA said the 2009 finding paved the way for electric vehicle mandates, and led to “significant uncertainties and massive costs” for the American people and automakers related to “general regulations of greenhouse gases from vehicles and trucks.”

The proposal, according to the EPA release, would remove all greenhouse gas standards for light-, medium-, and heavy-duty vehicles and heavy-duty engines, starting with the EPA’s first greenhouse gas regulations set under the order in 2010, and including “off-cycle credits like the much-hated start-stop feature on most new cars.”

CBS News Chicago asked if Zeldin’s proposal could also eliminate vehicle emissions tests in Illinois. The Illinois EPA said it is too early to say, while Learner said this is the time the state can make a difference.

“We’re going to be looking for Illinois to step up to make sure people here have healthier, clean air,” said Learner.

The news release said if finalized, the proposal is expected to save Americans $54 billion in costs through the repeal of all greenhouse gas standards — including the Biden EPA’s electric vehicle mandate.

“If Congress wants to amend Section 202 of the Clean Air Act and tell us that they want us to be regulating the heck out of carbon dioxide, methane, and these other greenhouse gases, then we will follow the law,” said Zeldin.

The U.S. EPA proposal is not a done deal yet.

“We’ll go through a public comment period,” Zeldin said. “We’ll see what the American public has to say about everything that we put out right now — on all of this.”

The public comment period on this starts now and will last 45 days. Meanwhile, environmental groups are expected to take the U.S. EPA to court to challenge the rule.