And many people expect him to walk away from President Obama’s commitments under the Paris climate agreement and get rid of or weaken the E.P.A.’s Clean Power Plan, which requires states to lower carbon emissions from the electricity sector. He and his appointees might also try to water down fuel economy regulations for cars and trucks, and cut clean energy tax incentives and research spending.

States could blunt much of that damage. Even now, many states will be able to meet the Clean Power Plan’s targets by following through on planned investments and increasing energy efficiency, according to M. J. Bradley and Associates, a research and consulting firm. Some populous states have set targets that are even more ambitious and appear to be on track to meet them.

California and New York plan to cut greenhouse gas emissions to 40 percent below 1990 levels by 2030. Hawaii hopes to get all of its electricity from renewable sources by 2045. This month, Charlie Baker, the Republican governor of Massachusetts, proposed new rules for power plants and vehicles to make sure the state achieves its goal of a 25 percent cut from 1990 levels by 2020. Emissions are already down by around 20 percent.

Cheap natural gas, which has increasingly replaced coal as a fuel source, has had a lot to do with this progress, but so has the drop in the cost of wind and solar power — 41 percent in the case of land-based wind turbines and 64 percent for solar, between 2008 and 2015, according to the Energy Department. The cost of batteries has dropped by almost three-fourths. In some states, including Iowa, Illinois, Kansas, Nebraska and parts of Texas, new wind turbines can generate electricity at a lower cost, without subsidies, than any other technology, according to a report published this month by researchers at the University of Texas at Austin.

Solar panels have not reached that point yet in the United States, but developers of big solar installations in countries like Chile, Morocco and the United Arab Emirates have signed contracts to sell electricity for much less than conventional fossil fuel plants charge, according to Bloomberg New Energy Finance.