Abstract
Accurate estimation of effective radiative forcing (ERF) is essential for understanding climate responses to external forcing. A common approach involves simulations with fixed sea surface temperatures (SSTs) while allowing land temperatures to evolve freely. However, this setup can introduce land-induced adjustments that influence ERF estimates. Using a state-of-the-art climate model, we investigate the influence of land surface temperature changes in shaping ERF under an abrupt quadrupling of CO 2 (4xCO 2 ). We conduct a series of experiments where land temperatures and soil moisture are either interactive or prescribed to their climatological values. We find that fixing land temperatures and soil moisture increases 4xCO 2 ERF from 8.26 to 9.78 W m −2 , primarily due to reduced longwave cooling and cloud changes. Additional idealized experiments demonstrate a monotonic decrease in 4xCO 2 ERF but enhanced land precipitation with increasing land warming but fixed SSTs. These findings highlight the critical role of land processes in shaping radiative forcing estimates and provide insights into how land-sea warming contrasts influence convection, moisture transport, and precipitation patterns.