Quantifying the Influence of the Sea Surface Temperature Pattern Effect on Transient Global Warming

Abstract The pattern of surface warming plays a significant role in Earth’s response to radiative forcing as it influences climate feedbacks. Distinct patterns of surface warming lead to different equilibrium and transient responses to identical forcing, emphasizing the need to analyze this pattern effect. While existing studies have primarily focused on assessing the influence of surface warming patterns on long-term warming (equilibrium climate sensitivity, committed warming), their role in the transient global warming remains partially understood. Here, we introduce a novel analytical method to quantify the influence of the pattern effect on transient global warming. We use an energy budget which explicitly separates the radiative response caused by uniform global surface warming from the response induced by changing surface temperature patterns. Using this new energy balance model, we assess the relative contribution of the radiative response induced by changing surface temperature patterns to global warming in idealized forcing experiments (1pctCO 2 ) from 12 CMIP6 models. We show that the pattern effect consistently dampens global warming in 9 out of 12 models at decadal time scales. We specifically quantify that the pattern effect induces a change in the transient climate response of −6.0% [−11.3%; 0.5%] (mean and quantiles 17–83) compared to a scenario where the warming pattern is uniform. Our study demonstrates that distinct models exhibit significantly different transient global warming with differences being amplified by variations in the pattern effect. Overall, our results highlight the importance of changing warming patterns, through the pattern effect, in influencing decadal-scale transient warming. These findings support recent suggestions to incorporate warming pattern uncertainties in future climate projections.