Two Aspects of Decadal ENSO Variability Modulating the Long-Term Global Carbon Cycle

The El Niño–Southern Oscillation (ENSO) drives variations in terrestrial carbon fluxes by affecting the terrestrial ecosystem via atmospheric teleconnections and thus plays an important role in interannual variability of the global carbon cycle. However, we lack such knowledge on decadal time scales, that is, how the carbon cycle can be affected by decadal variations of ENSO characteristics. Here we examine how, and by how much, decadal ENSO variability affects decadal variability of the global carbon cycle by analyzing a 1,801-year preindustrial control simulation. We identify two different aspects, together explaining ~36% of the decadal variations in the global carbon cycle. First, climate variations induced by decadal ENSO-like variability regulate terrestrial carbon flux and hence atmospheric CO₂ on decadal time scales. Second, decadal changes in the asymmetrical response of the terrestrial ecosystem, resulting from decadal modulation of ENSO amplitude and asymmetry, rectify the background mean state, thereby generating decadal variability of land carbon fluxes.