WASHINGTON — President Obama on Monday named two people to his cabinet who will be charged with making good on his threat to use the powers of the executive branch to tackle climate change and energy policy if Congress does not act quickly.

Mr. Obama nominated Gina McCarthy, a tough-talking native of Boston and an experienced clean air regulator, to take charge at the Environmental Protection Agency, and Ernest J. Moniz, a physicist and strong advocate of natural gas and nuclear power as cleaner alternatives to coal, to run the Department of Energy.

The appointments, which require Senate confirmation, send an unmistakable signal that the president intends to mount a multifaceted campaign in his second term to tackle climate change by using all the executive branch tools at his disposal.

But even with Ms. McCarthy and Mr. Moniz in place, Mr. Obama would have to confront major hurdles in trying to refashion the American way of producing and consuming energy, the same hurdles that stymied climate and energy policy in his first term.