Nominees for Donald Trump's cabinet faced tough questions during confirmation hearings on Wednesday, where his pick to head the Environmental Protection Agency said climate change is real, breaking with his own past statements and those of the president-elect.

In response to questions from Democrats, Oklahoma Attorney General Scott Pruitt said he disagreed with Trump's earlier claims that global warming is a hoax created by the Chinese to harm the economic competitiveness of the United States.

"I do not believe climate change is a hoax," Pruitt said.

The 48-year-old Republican has previously cast doubt on the extensive body of scientific evidence showing that the planet is warming and human-made carbon emissions are to blame.

In a 2016 National Review opinion article, Pruitt suggested that the debate over global warming "is far from settled" and he claimed that "scientists continue to disagree about the degree and extent of global warming and its connection to the actions of mankind."

At the hearing before the Senate energy and public works committee, Pruitt conceded that human activity contributes "in some manner" to climate change. He continued, however, to question whether the burning of fossil fuels is the primary reason.

Pressed by Democratic Senator Bernie Sanders of Vermont to answer in detail about his beliefs about climate change, Pruitt responded that his personal opinion was "immaterial" to how he would enforce environmental laws.

In his current post, Pruitt joined a multi-state lawsuit opposing the Obama administration's plan to limit planet-warming carbon emissions from coal-fired power plants. Pruitt also sued over the EPA's recent expansion of water bodies regulated under the Clean Water Act. It has been opposed by industries that would be forced to clean up polluted wastewater.

Pruitt said that if he is confirmed by the Republican-run Senate, he would work with states and industry to return the federal watchdog to what he described as its proper role.

"Environmental regulations should not occur in an economic vacuum," Pruitt said. "We can simultaneously pursue the mutual goals of environmental protection and economic growth."

Health pick grilled over plans end Obamacare 

Offering reassurances, Tom Price, Trump's pick for health secretary, said the new administration won't "pull the rug out" from those covered by Obamacare. Democrats said they were unimpressed, noting a lack of specifics.

The Affordable Care Act is providing coverage to about 20 million people, and government as well as private experts say repealing without a concrete substitute would leave millions uninsured and spike premiums.

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Tom Price, a leading critic of the Affordable Care Act, testified he would not 'pull the rug out' from under those being helped by President Barack Obama's signature health-care law. (Alex Wong/Getty Images)

Representative Price, a Republican from Georgia, also told the Senate health, education, labour and pensions committee that Trump is "absolutely not" planning to launch an overhaul of Medicare as he tries to revamp coverage under President Barack Obama's signature health-care law.

He acknowledged that high prescription drug costs are a problem, but did not endorse the idea of the federal government directly negotiating prices.

Throughout the nearly four-hour hearing, Democrats peppered Price with questions about his stock trades. The sometimes confusing exchanges involved different transactions under distinct circumstances. Price, who has signed a government ethics agreement to sell his stock, balked at the suggestion that he profited from his official position.

"I'm offended by that insinuation," he told Senator Elizabeth Warren, a Massachusetts Democrat. 

Committee chairman Lamar Alexander, a Tennessee Republican, lauded Price's performance, but Democrat Patty Murray of Washington said she remains deeply concerned. No Democrats offered support for the 62-year-old nominee, an orthopedic surgeon.

Commerce secretary pick vows to redo NAFTA

Breaking with Republican orthodoxy, a new Trump administration will work quickly to redo the North American Free Trade Agreement (NAFTA), a massive trade pact with Canada and Mexico that has boosted trade but still stings laid off workers across the Midwest, Trump's pick for commerce secretary told his confirmation hearing.

Billionaire investor Wilbur Ross said all trade agreements should be systematically reopened every few years to make sure they are working in the best interests of the U.S.

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Wilbur Ross, picked by Trump to serve as his commerce secretary, told the Senate commerce committee he will work to swiftly renegotiate NAFTA. (Joe Raedle/Getty Images)

Ross said he is in favour of free trade, but noted his close relationship with the United Steelworkers union as proof that he will fight to protect American jobs. The union has endorsed him.

"NAFTA is logically the first thing for us to deal with," Ross said. "We must solidify relationships in the best way we can in our own territory before we go off to other jurisdictions.

"That will be a very, very early topic in this administration," Ross added. "I think all aspects of NAFTA will be put on the table."

Trump's views on trade are at odds with most congressional Republicans, who generally support America's trade pacts as a way to boost U.S. exports and to provide affordable consumer goods.

But trade is a divisive issue in much of the country, and Trump's attacks on NAFTA and other pacts during the election played well in parts of Pennsylvania, Ohio, Michigan and Wisconsin — all states the businessman won.

Ross's remarks on trade were welcomed by some Democrats, who are generally less enthusiastic than Republicans about trade agreements.

Afterward, Senator John Thune, a South Dakota Republican, said Ross allayed fears that a Trump administration would start a trade war.​

UN ambassador critical of global body 

Trump's pick for UN ambassador echoed his condemnation of the world body and pledged to push for reforms at her confirmation hearing on Wednesday.

South Carolina Gov. Nikki Haley repeated criticism of the United Nations before the Senate foreign relations committee, especially for what she termed its "bias" against Israel.

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Gov. Nikki Haley, Trump's pick for UN ambassador, told the Senate foreign relations committee she does not want to slash the global body's funding. (Mark Wilson/Getty Images)

Some Republicans want to stop U.S. funding for the United Nations over a Security Council resolution last month demanding an end to settlement building that the United States declined to veto, instead of abstaining.

Haley pledged that she would not abstain on UN votes, but said she did not back "slashing" UN funding.

The United States provides 22 per cent of the UN budget. Trump took to Twitter in the wake of the Israel vote to criticize the 193-member world body as "just a club for people to get together, talk and have a good time."

He warned "things will be different" after he takes office, without offering details. Haley said Washington should always back Israel.

Haley said she "absolutely" backs moving the U.S. Embassy to Jerusalem from Tel Aviv. That shift, which would change decades of U.S. policy, is supported by Trump and congressional Republicans but seen by the Palestinians and many Arab states as an impediment to Middle East peace. 

With files from Reuters