Coal use has been declining for decades, but ending the use of the fuel isn’t going to be easy, even in a place like California, which has ambitious climate change goals.

In the high desert just south of Death Valley, the hottest place on earth, two small coal plants have been running for 50 years. They provide heat and power to Searles Valley Minerals, a mining and processing plant in Trona, Calif., that churns out raw materials used in wind turbine blades, solar panels, pesticides and other products.

One of the two plants will shut down within the next two years and be replaced with a type of solar-thermal energy system that has been little used in the United States. But the other plant could stick around for many years and be used at a reduced rate because the mining company needs a power source that can run all day and generate heat to run the operation’s steam-driven equipment.

“That has been our struggle,” said Dennis Cruise, president of Searles Valley Minerals. “We’ve looked at everything. It’s a real challenge.”

In industry, many companies use coal, natural gas and other fossil fuels to achieve the high temperatures needed to make their products. And while start-ups and researchers are working on ways to produce heat without generating greenhouse gases, many of those approaches are not yet affordable or cannot produce heat that is hot enough.

About half of the world’s energy is used for heat, which includes keeping people warm, according to the International Energy Agency. Transportation and electricity accounts for the other half.