Decadal variability of Earth’s energy balance in CMIP6

Abstract:

Acting as both signal and noise, internal climate variability may confound estimates of the climate response to forcing but offers an opportunity to examine the dynamics controlling Earth's energy budget. This study analyzes the impact of low-frequency internal variability on global-mean surface temperature (GMST) and the top-of-atmosphere (TOA) radiative imbalance in CMIP6 pre-industrial control simulations. We identify slow modes of variability using low-frequency component analysis (LFCA). The slow modes of variability with the largest impact on decadal-mean GMST are focused in high-latitude ocean regions, where they have minimal impact on the TOA radiative imbalance. When these regions warm, positive shortwave cloud and sea-ice radiative feedbacks largely cancel the negative feedback of outgoing longwave radiation, resulting in a weak net radiative feedback. The weak net radiative feedback means that less energy is required to sustain these long-lived temperature anomalies. These results suggest that on decadal and longer timescales, different processes control internal variability in GMST than control internal variability in TOA radiative imbalance. We discuss how low-frequency internal variability contributes to uncertainty in estimates of climate sensitivity from decadal-mean GMST and TOA-radiative-imbalance anomalies.