House Speaker Paul Ryan listens to US President-elect Donald Trump speak to the press at the Capitol in Washington, DC, on November 10, 2016.

Unified Republican control of the federal government over the next two years augurs a sea change in US environmental policy like nothing since the late 1960s and '70s, when America's landmark environmental laws were first passed.

If Donald Trump and the GOP actually follow through on what they've promised, this time around will be a lurch in the opposite direction. Federal climate policy will all but disappear; participation in international environmental or climate treaties will end; pollution regulations will be reversed, frozen in place, or not enforced; clean energy research, development, and deployment assistance will decline; protections for sensitive areas and ecosystems will be lifted; federal leasing of fossil fuels will expand and accelerate; new Supreme Court appointees will crack down on EPA discretion.