Marine low clouds are one of the greatest sources of uncertainty for climate projection. We present an observed climatology of cloud albedo susceptibility to cloud droplet number concentration perturbations (S0) with changing sea surface temperature (SST) and estimated inversion strength for single‐layer warm clouds over the North Atlantic Ocean, using eight years of satellite and reanalysis data. The key findings are that SST has a dominant control on S0 in the presence of co‐varying synoptic conditions and aerosol perturbations. Regions conducive to aerosol‐induced darkening (brightening) clouds occur with high (low) local SST. Higher SST significantly hastens cloud‐top evaporation with increasing aerosol loading, by accelerating entrainment and facilitating entrainment drying. In a global‐warming‐like scenario where aerosol loading is reduced, less cloud darkening is expected, mainly as a result of reduced entrainment drying. Our results imply a less positive low‐cloud liquid water path feedback in a warmer climate with decreasing aerosol loading. Plain Language Summary Low clouds over the ocean are a poorly quantified component of the climate system. Here we use eight years of space‐based measurements and meteorological data to quantify how the brightness of single‐layer low clouds over the North Atlantic Ocean might respond to cloud droplet number concentration perturbations in a warmer world. We find that under higher sea surface temperatures, increases in drop number tend to reduce cloud brightness by accelerating evaporation of cloud water. Thus in a warmer world, low clouds will reflect less energy to space in response to an increase in aerosol loading. If aerosol sources decrease then we expect more robust clouds and more offsetting of greenhouse gas warming. Key Points Sea surface temperature (SST) has a strong influence on the relative occurrence of aerosol‐induced brightness of clouds over the North Atlantic Ocean Aerosol perturbations are locally confined and have less influence on the brightness of clouds compared to SST In a warmer climate where aerosol loading is reduced, we expect a less positive liquid water path feedback