Global expansion of the sensitive aerosol-limited marine cloud regime under emission reductions

Aerosol-cloud interactions (ACIs) are fundamentally nonlinear, with their strongest climatic effects emerging where cloud properties are highly sensitive to aerosol changes-the aerosol-limited regime. Quantifying this regime's evolution is therefore critical for constraining uncertainties in climate forcing and future projections. By integrating satellite observations with climate model simulations, we map this regime globally and track its recent change. We find it expanded by 4.8% per decade over the past 20 years, primarily due to a sharp increase (∼14.7% per decade) in the Northern Hemisphere driven by anthropogenic emission reductions. Under a strong emission reduction pathway, its frequency is projected to double or triple in key ocean regions. This systematic shift pushes marine clouds into a state of heightened aerosol sensitivity, thereby amplifying the cloud-mediated radiative response to aerosol changes. Our findings underscore the need to account for this evolving sensitivity in climate projections.