Predictability Horizons in the Global Carbon Cycle Inferred From a Perfect-Model Framework

Abstract

On interannual timescales the growth rate of atmospheric CO2 is largely controlled by the response of the land and ocean carbon sinks to climate variability. Yet, it is unknown to what extent this variability limits the predictability of atmospheric CO2 variations. Using perfect-model Earth System Model simulations, we show that variations in atmospheric CO2 are potentially predictable for 3 years. We find a 2-year predictability horizon for global oceanic CO2 flux with longer regional predictability of up to 7 years. The 2-year predictability horizon of terrestrial CO2 flux originates in the tropics and midlatitudes. With the predictability of the isolated effects of land and ocean carbon sink on atmospheric CO2 of 5 and 12 years respectively, land dampens the overall predictability of atmospheric CO2 variations. Our research shows the potential of Earth System Model-based predictions to forecast multiyear variations in atmospheric CO2.