Irreversible changes in the sea surface temperature threshold for tropical convection to CO2 forcing

Tropical convection plays a critical role in modulating the global climate by influencing climate variability. However, its future projection under climate mitigation scenarios remains uncertain. Here, we found that while the relationship between precipitation intensity and upward motion remains constant regardless of changing CO2 concentrations, the sea surface temperature threshold for tropical convection and the convective zone exhibit hysteretic and irreversible behavior. As the CO2 concentration decreases from its peak (ramp-down), higher tropical ocean temperature leads to higher sea surface temperature thresholds for convection than during the period of increasing CO2 concentration (ramp-up), while convective instability remains the same during both ramp-up and ramp-down. El Niño-like warming during the ramp-down leads to a weakening of the Walker circulation and an expansion of the convective zone in the central to eastern tropical Pacific by a warmer-get-wetter mechanism. Our results suggest that CO2 removal does not guarantee the recovery of tropical convection. The sea surface temperature threshold for tropical convection and convective zones shows irreversible behavior, suggesting that mitigation efforts may not fully offset tropical convective activities, according to results from different climate mitigation scenarios to analyze tropical convection and its physical mechanisms.