Senne Van Loon, Maria Rugenstein, Elizabeth A Barnes

Human emissions continue to influence Earth's climate. Effective radiative forcing quantifies the effect of such anthropogenic emissions together with natural factors on Earth's energy balance (Soden et al. 2018; Gregory et al. 2020; Forster et al. 2021, 2024). Evaluating the exact rate of effective radiative forcing is challenging, because it can not be directly observed. Therefore, estimating the effective forcing usually relies heavily on climate models (Forster et al. 2024). Here, we present an estimate of effective radiative forcing that makes optimal use of observations. We use artificial intelligence to learn the relationship between surface temperature and radiation caused by internal variability in a multi-model ensemble. Combining this with observations of surface temperature and the Earth's net radiative imbalance (Loeb et al. 2018, 2021; NASA/LARC/SD/ASDC 2023), we predict an effective forcing trend of 0.72+-0.20 Wm^{-2} per decade for 2001-2023. Our method enables a new and independent assessment of the observed effective radiative forcing since 1985, that can be updated simultaneously with available observations. We make advances to close the Earth's energy budget on annual timescales, separating the influence of forcing versus the radiative response to surface temperature variations. Effective radiative forcing has substantially increased since 2021 and has not been countered by a strongly negative radiative response, consistent with an exceptionally warm year of 2023 and 2024.