In energy, geothermal breakthroughs are generating tremendous excitement. As David Roberts notes in an excellent explainer in Vox, the molten core of the earth is about 10,000 degrees Fahrenheit, roughly the same temperature as the sun. If we could tap 0.1 percent of the energy under the earth’s surface we could supply humanity’s total energy needs for two million years.

Engineers are figuring out how to mine the heat in the nonporous rock beneath the surface. As Roberts writes, “If its more enthusiastic backers are correct, geothermal may hold the key to making 100 percent clean electricity available to everyone in the world.”

This is not even to mention fusion. In one of those stories that felt epochal when you read it, my Times colleague Henry Fountain reported last September on how M.I.T. researchers had designed a compact nuclear reactor that should work. China currently has an experimental thermonuclear reactor that is reaching 270 million degrees Fahrenheit.