This result confirms the importance of rapid responses in the atmosphere to changes in black carbon. These responses manifest themselves as warming at height and changes in cloud properties that lead to a net decrease in mid- and high-level cloud (Fig. 1). Moreover, they act to offset the initial artificially large perturbation, mainly because the warming and cloud loss at altitude effectively radiate energy to space, before the surface climate is able to respond. However, the magnitude of the rapid responses reported by Sand et al. — roughly seven times stronger than those to carbon dioxide — will come as a surprise to many climate scientists.