Systematic Observation-Based Estimate of Effective Radiative Forcing from Aerosol–Cloud Interactions

Abstract. The change in Earth's energy budget caused by anthropogenic aerosols interacting with clouds is the most uncertain contributor to the historical energy budget trend, with important implications for future climate projections. Recent studies estimating the effective radiative forcing from aerosol-cloud interactions (ERF_aci) using satellite observations and a Cloud-Controlling Factor (CCF) analysis have produced a large spread of results, ranging from approximately -0.3 to -1.5 Wm^-2. This spread is comparable to the full IPCC AR6 uncertainty range, reflecting the use of different datasets and methodological choices across studies, often without a systematic basis for selecting among them. Here we develop a unified framework to rigorously evaluate these methodological choices across multiple reanalysis datasets, using both climate model simulations and observed regional aerosol trends as independent validation tests. Applying model based bias-correction to the best configuration yields a best-estimate global ERF_aci of -0.84 Wm^-2 (66% confidence interval: -1.21 to -0.47 Wm^-2) and an implied Equilibrium Climate Sensitivity of 3.33K (66% confidence interval: 2.65 to 4.22K), both consistent with IPCC AR6 and WCRP 2019 assessments but different from previous CCF-based estimates.