President Trump and the head of the EPA announced a major change for greenhouse gas emissions, repealing what is known as the "endangerment finding," which provides the underpinning for federal government environmental regulations.
But what does it really mean and how will it impact the air we breathe?
The EPA first announced its proposal to revoke what's called the "endangerment finding" last June, so Thursday's move by the Trump administration didn't come out of left field.
It's why, for months, environment and climate experts have been sounding the alarm.
"Effective immediately, we are repealing the ridiculous 'endangerment finding' and terminating all additional green emission standards," the president said.
The move means the United States Environmental Protection Agency will no longer regulate greenhouse gases emitted from sources like cars, trucks and power plants.
The president said the move will help the American auto industry and bring down prices of cars.
"This action will eliminate over $1.3 trillion of regulatory costs and help bring car prices tumbling down dramatically," Mr. Trump said.
Greenhouse gas emissions are scientifically proven to contribute to climate change, according to experts, and until now the government supported rules on emissions.
"Deregulation sounds like a great thing until you look at the consequences of the actual action," said Susan Mudd, an attorney and policy advocate for the Environmental Law & Policy Center, where she leads the Diesel Pollution Reduction Initiative. "It's undoing the government's finding based on all the science."
The "endangerment finding," now revoked, provided the government the legal and scientific foundation to regulate emissions - helping reduce risks of worsening heat waves, wildfires, droughts and floods.
"That's what we are going to see more of - damaging storms, flooding, and worse air pollution," Mudd said. "What we will expect to see right away are pullbacks on the various automobile standards, truck standards, power plant standards."
"It's going to affect badly the public health of our grandchildren, our children, and the future generations of the people of Illinois for many years to come," said Nicole Cantello, president of the EPA workers' union in the Chicago area.
She said the majority of EPA workers do not agree with this move.
"Through the union, we will do everything that we can and use every power that we have to protect the people of the Great Lakes like we have been doing for all of our careers as EPA workers," she said.
So, what's next? Experts said it's likely the Trump administration is taken to court over whether it can legally erase the government's own scientific and statutory conclusions.