Donald Trump wants to cut the US Environmental Protection Agency’s spending by about $2.4bn— nearly a third of its budget — which would force the cancellation of all research into climate change.
In total some 3,200 employees, roughly one in five of the EPA’s workforce, would lose their jobs.
Even the agency’s work on air and water quality would have to be reduced.
The proposals must still be agreed by Congress, which is controlled by Mr Trump’s Republican party, although he has faced opposition from within its ranks to his more outlandish statements and policies.
Mick Mulvaney, of the White House Office of Management and Budget, told reporters: “You can’t drain the swamp and leave all the people in it.
“So, I guess the first place that comes to mind will be the Environmental Protection Agency.
“The president wants a smaller EPA. He thinks they overreach, and the budget reflects that.”
The budget would fall from $8.1bn to $5.7bn (£6.6bn to £4.1bn), under the plan, while the workforce would fall from about 15,000 to 11,800.
The Clean Power Plan, which was introduced by Barack Obama to try to reduce greenhouse gas emissions from power stations, would be scrapped, among more than 50 other EPA initiatives.
John O’Grady, a leading union official who works for the EPA, told The Washington Post the agency was “already on a starvation diet, with a bare-bones budget”.
“The administration’s proposed budget will be akin to taking away the agency’s bread and water,” he said.
And Cynthia Giles, who led the EPA’s Office of Enforcement and Compliance Assurance during the Obama administration, told the Post that more cuts “won’t just drastically reduce EPA enforcement, it will bring it to a halt”.
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“Not only will the staff be a shadow of its former self, the inspectors, lawyers and criminal agents who would be left would be unable to do their jobs, because these cuts would zero out the already small amount of funds used to do inspections, monitor pollution and file cases,” she said.
Mr Trump has spoken about protecting jobs in the coal industry at a time when many countries, including the UK, are starting to phase out the dirtiest form of fuel.
However attempts to capture emissions from coal-fired power plants in a cost-effective way, so they do not contribute to global warming or pollute the atmosphere, are still ongoing. Mr Trump has talked about trying to promote this ‘clean coal’.
A summary of the Trump administration’s EPA budget plan said: “Consistent with the President's America First Energy Plan, the budget reorients the EPA's air program to protect the air we breathe without unduly burdening the American economy.”
Environmental groups expressed dismay at the proposals.
Manish Bapna, managing director of the World Resources Institute, said the budget plan "continues the administration’s shocking disregard for priorities that are critical for people’s health and the economy".
"The US government must have the resources to protect air, water and people’s health at home," he said.
“The government should also invest in American innovation, especially to accelerate the clean energy revolution that is already reducing pollution and creating more domestic jobs.
“The administration should respect science and continue to respond to the growing impacts of climate change, which is understood by the scientific and security communities alike.
"Human-caused climate change is already contributing to severe droughts and food shortages and accelerating the migration of people. Slashing climate and clean energy funds will undermine US business and diplomatic interests and lead to greater security risks for us all.
“It’s now up to Congress to restore funding, recognising that America’s economic and security interests are intertwined with the well-being of people and the planet.”
Reuters contributed to this report