It’s been known for a while now that oceans are the biggest carbon sinks in the world. But until recently scientists weren’t sure where all the land-based ones were. If you thought forests were the only good carbon sinks, think again. Turns out, desert endorheic basins—ones where water flows in but disappears into the ground or evaporates instead of flowing out—play a bigger role in storing carbon than thought, but that role could be endangered because of climate change.

An arid endorheic basin in South Australia.
Credit: BRJ Inc./flickr

Though scientists know how much carbon dioxide humans emit each year, they don’t know exactly what happens to the carbon that is absorbed by the land. About 40 percent of human carbon emissions stay in the atmosphere, about 30 percent is absorbed by the world’s oceans, and the rest is absorbed by carbon sinks on land, according to the National Center for Atmospheric Research.

Arid regions, which cover about 47 percent of the earth’s land mass, are thought to make up the world’s third-largest carbon sink on land.

As the world continues to warm, climate change may affect the water cycle, reducing the ability of desert basins to act as carbon sinks. Carbon that would be naturally stored in the soil may return to the atmosphere as soil moisture evaporates in higher temperatures.

The ability of deserts and other ecosystems to sequester human carbon emissions is critical to climate policies such as the Paris climate agreement because it’s a major factor in calculating how quickly atmospheric carbon will accumulate in the atmosphere. As less carbon is absorbed by the land and oceans, more remains in the atmosphere.

Read more about Desert Basins Could Hold ‘Missing’ Carbon Sinks at Climate Central