Attributing Radiative Feedback Evolution to Regional Ocean Heat Uptake

Abstract:

Radiative feedbacks are found to vary with time in both historical records and future warming projections. Previous studies proposed two factors that determine the variation of radiative feedbacks: (i) the evolution of tropical surface warming pattern and (ii) the tropical-extratropical contrast of ocean heat uptake. Our results bridge the two factors by evaluating the remote impact from the extratropical ocean on tropical SST pattern, accounting for the time evolution of net radiative feedback in response to abrupt quadrupling of CO₂. Based on the Green’s Function approach that quantifies the contribution of ocean heat uptake, we show that the net radiative feedback evolution in Community Earth System Model (CESM) can be mostly attributed to the ocean heat uptake over the Southern Ocean. The enhanced surface warming associated with the weakened ocean heat uptake decades after quadrupling CO₂ is not confined over the Southern Ocean, but extends to tropical Southeastern Pacific, which leads to decreasing tropospheric stability and increasing net radiative feedback. Our work highlights the critical role of Southern Ocean in modifying the time evolution of tropical SST pattern and radiative feedbacks in future warming projections.