The New York Times Editorial Board.

Had Donald Trump spent an entire year scouring the country for someone to weaken clean air and clean water laws and repudiate America’s leadership role in the global battle against climate change, he could not have found a more suitable candidate than Scott Pruitt, the Oklahoma attorney general, whom he picked on Wednesday to run the Environmental Protection Agency.

This is an aggressively bad choice, a poke in the eye to a long history of bipartisan cooperation on environmental issues, to a nation that has come to depend on the agency for healthy air and drinkable water, and to 195 countries that agreed in Paris last year to reduce their emissions of climate-changing greenhouse gases in the belief that the United States would show the way. A meeting Monday between Mr. Trump and Al Gore had raised hope among some that the president-elect might reverse his campaign pledge to withdraw the United States from the Paris accord. The Pruitt appointment says otherwise.

Since becoming Oklahoma’s top legal officer in 2011, Mr. Pruitt has been a bitter opponent of the E.P.A., joining in one lawsuit after another to kill off federal environmental regulations. He has challenged standards for reducing soot and smog pollution that cross state lines. He has fought protections against mercury, arsenic and other toxic pollutants from power plants. He has sued to overturn an E.P.A. rule modestly enlarging the scope of the Clean Water Act to protect streams and wetlands vital to the nation’s water supply.

More recently — and of greater interest to the world community — he has joined with other states in a coordinated effort to overturn the E.P.A.’s Clean Power Plan, the centerpiece of President Obama’s regulatory efforts to reduce carbon pollution. If approved by a federal court, the plan could transform the electricity sector, close down hundreds of coal-fired power plants and encourage the growth of cleaner energy sources like wind and solar.

The plan is crucial to Mr. Obama’s commitment in Paris to reduce America’s overall greenhouse gas emissions by 26 percent to 28 percent below 2005 levels by 2025, as part of a global effort to keep atmospheric warming from exceeding a level beyond which, scientists believe, the world could be locked into a future of rising sea levels, extended droughts and other devastating consequences. Should a Trump administration step back from that commitment, other nations could follow suit, rendering the Paris agreement irrelevant and driving the world toward irreversible climate change.

Mr. Pruitt has repeatedly suggested that the science of climate change is far from settled, when in fact it is, and says that scientists continue to disagree about whether there is a relationship between human activity and rising atmospheric temperatures, which they don’t. With each successive report, the thousands of scientists charged with monitoring global warming and its causes for the United Nations’ Intergovernmental Panel on Climate Change have reaffirmed and indeed strengthened that connection.

In much of what he has done, Mr. Pruitt has tended to the interests of the oil and gas industries, no surprise in Oklahoma, where oil and gas are important. But he has gone far beyond that. An investigation by The Times in 2014 found that Mr. Pruitt had helped organize an “unprecedented, secretive alliance” between Republican attorneys general and large energy companies to attack the E.P.A. — and one of the letters he sent complaining to the agency had in fact been written by industry lawyers.

Mr. Pruitt is the wrong person to lead an agency charged with custody of the nation’s environment. If the Senate cares about the public good, it needs to send his nomination to the dust bin.