Earth’s soils store about 1.5 trillion metric tons of organic carbon—more than is contained in the planet’s vegetation and atmosphere combined. But that soil carbon isn’t necessarily a permanent fixture: It can be lost when microbes digest it and respire CO2. In a mature forest in a stable climate, carbon released from the soil to the atmosphere is in equilibrium with carbon absorbed from the atmosphere. In a world warmed by climate change, though, the balance may tip.
Generally, an increase in soil temperature accelerates the rate of microbial respiration and therefore the rate of CO2 release to the atmosphere. However, climate models struggle to predict how much more CO2 soil microbes release in response to rising temperatures and that uncertainty is amplified by differences in the mean annual temperatures for different latitudes. Measurements in temperate and Arctic forests have shown that high-latitude soils—including permafrost—that contain...
