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The pattern of surface warming plays a significant role in the Earth’s response to radiative forcing as it influences climate feedbacks. Distinct patterns of surface warming lead to divergent equilibrium and transient responses to identical forcing, emphasizing the need to analyse 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 on the transient global warming remains poorly understood. Here, we introduce a novel analytical method to quantify the importance of evolving surface warming patterns on transient global warming. Our approach involves explicitly separating the radiative response caused by the global surface warming from the additional response induced by changing surface temperature patterns in the global energy budget. 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 (1pctCO2) from 12 CMIP6 models. We show that the pattern effect consistently dampens global warming in 11 out of 12 model at decadal time scales. Specifically, we quantify that the transient climate response is reduced on average by 11% because of changing warming patterns. Our study demonstrates that distinct models exhibit significantly divergent transient global warming solely due to 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.