Observational Evidence of Increasing Global Radiative Forcing

Abstract:

Change in atmospheric composition, such as increasing greenhouse gases, causes an initial radiative imbalance to the climate system, quantified as the instantaneous radiative forcing. All climate change is a response to this imbalance. Although modeled with high accuracy, this fundamental metric has not been directly observed globally. In part, this is because current space-based instruments cannot distinguish the instantaneous radiative forcing from the climate’s radiative response. We apply radiative kernels to satellite observations to separate these components and find all-sky instantaneous radiative forcing has increased 0.53 +/- 0.11 W/m² from 2003 through 2018 in CERES radiative flux observations, almost entirely accounting for positive trends in the total radiative imbalance. We demonstrate that a combination of rising well-mixed greenhouse gases and recent reductions in aerosol emissions account for the trend and that the observed changes closely agree with reanalysis, offline radiative transfer calculations and well-established empirical estimates. This lends credence to the ability of our current satellite observing system to measure long-term climate change, despite instrumental uncertainties. We find these radiative forcing trends are detectable within 4 years. Our results highlight the distinct fingerprints of anthropogenic activity in observations of Earth’s changing energy budget.