President Trump's nominees to serve on the Federal Energy Regulatory Commission stressed on Thursday that they would adhere to the commission's basic duties of approving and regulating the interstate transmission of electricity, natural gas, and oil, without favoring one energy source over another.

Nominees Kevin McIntyre, Trump's Republican FERC chairman-in-waiting, and Rich Glick, a Democratic attorney, testified at the Senate Energy and Natural Resources Committee that they would base their decisions on science.

"FERC does not pick fuels among different generating resources, so it's important it be open to the science, and the characteristics of reliability and economics that are important to satisfying the energy needs of our nation," McIntyre testified.

"Our first role, rather, is to ensure the markets for the electricity generated by the facilities proceed in accordance in law," McIntyre added.

In recent years, the commission has become a major target by environmental groups who think its decisions don't account for the effects of climate change, and favor pipelines that help drive shale energy development. Some environmental protesters were at the hearing today, and chanted, "Mind your conscience, FERC is destroying our atmosphere" just before McIntyre testified.

McIntyre is a former energy industry adviser with the global firm Jones Day. Glick currently serves as general counsel for Democrats at the committee he visited Thursday.

Senators used the hearing to challenge the nominees to explain how their prospective jobs at FERC would interact with the nation's changing power grid.

Last month, the Energy Department released an anticipated report urging actions to protect the "reliability and resilience" of the nation's electric grid. The study raises concerns that a future grid with fewer "baseload" coal and nuclear plants, which can produce electricity around the clock, could present challenges.

Plentiful cheap natural gas, and the rise of wind and solar power, have reshaped the energy landscape as coal and nuclear plants have closed across the U.S. in recent years.

Sen. John Barrasso, a Republican representing Wyoming, a coal dependent state, asked McIntyre if he supports a recent statement by current FERC chairman Neil Chatterjee, a Republican, who said coal plants should be "properly compensated to recognize the value they provide."

McIntyre answered the question carefully.

"Coal has historically played an enormously important role in our nation's generation of electricity," he said. "The importance of such resources [including nuclear power] cannot be denied, however FERC is not an entity whose role includes choosing fuels for generation of electricity."

Glick was more explicit in rejecting any effort by FERC to tip the scale towards coal and nuclear power.

"The commission doesn't have authority, nor should it, to prop up failing technologies or technologies that are not economically competitive," he said.

Democrats on the committee, meanwhile, asked the nominees to describe any responsibilities they may have to pursue market changes that benefit renewable energy sources with a lower carbon footprint.

"What role does FERC have in ensuring a cleaner energy environment?" asked Sen. Tammy Duckworth, D-Ill., who noted her state's efforts at promoting cleaner energy sources.

McIntyre again stressed he would take a nonbiased approach.

"There is no question states have an absolute right to implement renewable standard portfolios," he said. "FERC is not an environmental regulator per se. It's important for FERC to keeps its eyes open to advance public policies where FERC's jurisdiction does extend if there are relevant environmental aspects."

Glick echoed McIntyre's perspective.

"I am not sure FERC has a straightforward direct role in promoting environmental enhancement," he said. "That's left up to the EPA and other agencies as well as the Congress. But I would say FERC has [a role] in terms of reducing barriers to cleaner technology that can help advance environmental benefits and also economic benefits as well."

In the past, FERC has had minimal obligations in considering greenhouse gas emissions and the effect on climate change when making decisions.

But that may change as a result of a ruling by the D.C. Circuit Court of Appeals last month that could force FERC members to more actively examine the effects of climate change when they review proposed natural gas pipelines.

"This is not your grandfather's FERC," said Sen. Angus King, I-Maine, jokingly imploring McIntyre and Glick to consider the changing responsibilities of commission members.

The confirmation hearing represented progress for FERC, which has been in turmoil during Trump's first six months in office.

The agency was forced to close down for the first time in its 40-year history due to a lack of members.

Two Republican commissioners confirmed by the Senate last month restored the quorum at its minimum level of three members. The commission will have its full five members, with the confirmation of McIntyre and Glick, but it is uncertain when they will come up for a vote.

"We can't get you there fast enough," said Sen. Lisa Murkowski, R-Alaska, the committee chairwoman, upon closing the hearing.