Forcing closure suggests stronger aerosol forcing and higher climate sensitivity than the consensus

Forcing together with radiative responses and natural variability has sharply increased Earth’s energy imbalance (EEI), a key driver of climate change, between 2003 and 2023. Declining anthropogenic aerosol emissions and increasing greenhouse gas concentrations are the leading contributors to the forcing. However, observation-based and model-based forcing estimates disagree on the magnitude of aerosol forcing, particularly for effective radiative forcing from aerosol-cloud interactions (ERF ACI ). Here, we show that two independent observation-based estimates of forcing trends achieve unexpectedly good closure between 2003 and 2023. The corresponding model-based trend is within the uncertainty range of observations but substantially smaller, with most of the difference due to models’ underestimation of cloud fraction adjustment to aerosols. Our results suggest a prominent role of aerosols in the recent EEI increase and stronger total historical ERF ACI and higher equilibrium climate sensitivity than the current consensus, with a likely range between 2.8° and 4.8°C.