US President-elect Donald Trump's controversial pick to run the Environmental Protection Agency acknowledged Wednesday that human activity affects climate change, but he insisted the extent of that impact remains subject to debate.

Scott Pruitt set out in his Senate confirmation hearing to counter critics who see hin as a climate skeptic intent on rolling back environmental regulations.

"Let me say to you: science tells us that the climate is changing, and that human activity in some manner impacts that change," he told senators.

"The ability to measure with precision the degree and extent of that impact, and what to do about it, are subject to continuing debate and dialogue, and well it should be."

Pruitt, who currently is Oklahoma's attorney general, was among four Trump cabinet nominees in confirmation hearings Wednesday.

The Senate's Republican leadership is pushing for quick confirmation so that Trump will have at least part of his team in place shortly after his inauguration on Friday.

As an ally of the fossil fuel industry who has repeatedly sued the EPA on behalf of Oklahoma utilities, the 48-year-old Pruitt is a particularly controversial choice to head the agency.

If confirmed, he would assume control of an agency that under outgoing President Barack Obama was responsible for implementing sweeping environmental regulations governing clean air and water, greenhouse gas emissions and vehicle fuel emissions.

- 'False paradigm' -

In picking him for the job, Trump said he was confident Pruitt will reverse the agency's "out-of-control anti-energy agenda."

Pruitt brushed off concerns about his connections to energy companies, many of which have contributed to his campaigns or offices in various forms.

"We must reject as a nation the false paradigm that if you're pro-energy, you're anti-environment," Pruitt said. "I utterly reject that narrative."

Opponents scoffed at Trump's suggestion that Pruitt will be a capable environmental steward.

Senate Democrat Sheldon Whitehouse of Rhode Island noted that his state's fisheries have been "crashing" due to climate change.

"I see nothing in your career to give those fishermen any confidence that you will care one bit for their well-being, and not just the well-being of the fossil fuel industry," Whitehouse told Pruitt.

Other Democrats raised concerns about how Pruitt would address mercury pollution from power plants, air quality and lead in US water.

On the campaign trail, Trump often echoed the position of his business-friendly, regulation-averse Republican Party.

In 2012, Trump declared global warming was a hoax "created by and for the Chinese in order to make US manufacturing non-competitive."

While he has moderated that position over the past year to acknowledge that human activity has some connection to climate change, he repeatedly floated the idea of dramatically curbing EPA power.

"Environmental protection, what they do is a disgrace. Every week they come out with new regulations," he said on Fox in October 2015.

Asked who will serve as stewards of the environment, Trump said: "We'll be fine with the environment."