a, Black-carbon emissions from sources such as industrial processes, brick kilns and forest fires have numerous influences on the atmosphere. The details of these influences can be strongly dependent on time and location, but the emissions generally lead to a net surface dimming (thin yellow arrows) alongside enhanced warming at height (pink shading). The latter factor is often associated with enhanced vertical convection and effects on clouds that have a net result, according to Sand and colleagues' climate simulations3, of reducing cloud at altitude (not shown). b, Sand et al. suggest that roughly half of the total climate impact of black-carbon emissions is apparent only if these atmospheric responses feed back to the distribution of black carbon, lofting it to height and increasing its atmospheric lifetime and spatial extent. These changes enhance any surface dimming (extension of thin yellow arrow), and lead to greater warming at height (upper pink shading), black-carbon transport into the upper atmosphere (dotted black arrow) and further changes to clouds. Although, locally, greater warming can generate some deepened convective clouds, the net impact is a further reduction of cloud at altitude.