A radioactive isotope produced by nuclear weapons reveals that plants take up more carbon—but hold on to it for less time—than current climate models suggest.

Current climate models underestimate how much carbon plants sequester but overestimate how long that carbon stays locked away, researchers report in Science. The findings could inform future strategies to store and manage atmospheric carbon dioxide (CO2).

“If we want to limit climate change and make policies that are going to keep us under a certain level of global warming, then we need to understand how the natural system is responding and how it’s serving as a carbon sink,” said study lead author Heather Graven, an atmospheric scientist at Imperial College London.

“We can’t rely on the biosphere to mop up our CO2,” Graven said. “We need to stop emitting it if we want to reduce or limit climate change.”