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. Terrestrial carbon uptake as high inter-annual variability which can be used to help understand future responses to climate change. Here the authors' modeling reveals a large portion of this variability is driven by human land use changes and management, and not captured by other models.