Contribution of land use to the interannual variability of the land carbon cycle

Understanding the driving mechanisms of the interannual variability (IAV) of the net land carbon balance (S_net) is important to predict future climate-carbon cycle feedbacks. Past studies showed that the IAV of S_net was correlated with tropical climate variation and controlled by semiarid vegetation. But today's land ecosystems are also under extensive human land use and management. Here, we report a previously hidden role of land use in driving the IAV of S_net by using an improved biosphere model. We found that managed land accounted for 30-45% of the IAV of S_net over 1959-2015, while the contribution of intact land is reduced by more than half compared with previous assessments of the global carbon budget. Given the importance of land use in modulating future land climate-carbon cycle feedbacks, climate mitigation efforts should strive to reduce land-use emissions and enhance the climate resilience of carbon sinks over managed land.