Intensification of the ENSO-related terrestrial carbon cycle under greenhouse warming

Interannual variation in the global carbon cycle, dominated by land uptake processes, is principally associated with El Niño-Southern Oscillation (ENSO). We investigate future changes in a sensitivity of land carbon uptake to the ENSO based on Earth System simulations. By comparing the control experiment and future projection, it is found that the ENSO-related terrestrial carbon flux is significantly intensified under greenhouse warming, suggesting that atmospheric CO2 concentration will be more strongly affected by the ENSO in the future. The enhanced terrestrial carbon flux associated with the ENSO is mostly contributed by changes in sensitivity of Gross Primary Production (GPP) to the ENSO over Amazon, Australia, and equatorial Asia. More detail analysis reveals that this change is contributed by increased land temperature response to the ENSO and enhanced GPP sensitivity to local temperature variation. Our results imply that there is high probability of carbon-cycle extremes in the tropics according to the ENSO in a warming world.