The United States will work with other governments to speed up efforts to make nuclear fusion a new source of carbon-free energy, U.S. Climate Envoy John Kerry said Tuesday, the latest of many U.S. announcements the past week aimed at combating climate change.

Nuclear fusion melds two hydrogen atoms together to produce a helium atom and a lot of energy — which could be used to power cars, heat and cool homes and other things that currently are often powered by fossil fuels like coal, oil and gas. That makes fusion a potentially major solution to climate change, which is caused by the burning of fossil fuels. Still, fusion is a long way off, while other clean technologies such as wind and solar are currently in use and could be increased.

“We are edging ever closer to a fusion-powered reality. And at the same time, yes, significant scientific and engineering challenges exist,” Kerry said at U.N. climate talks called COP28 in Dubai, United Arab Emirates. “Careful thought and thoughtful policy is going to be critical to navigate this.”

Researchers have been trying for decades to harness the reaction that powers the sun and other stars — an elusive goal because it requires such high temperatures and pressures that it easily fizzles out.

Kerry wants to speed that up in hopes of limiting global warming to 2.7 degrees since preindustrial times, a benchmark set by the international community. He urged nations to come together to “harness the power of fundamental physics and human ingenuity in response to a crisis.” Kerry spoke at the Atlantic Council Global Energy Forum.

Until now, all nuclear power has come from nuclear fission reactors in which atoms are split — a process that produces both energy and radioactive waste. Fusion doesn’t produce the radioactive waste of nuclear fission.