“Air pollution in the form of aerosol particulates . . . play an important role [in climate change], but because they are washed out by rainfall, their average lifetime is in the order of a week. Hence their effects are not global but rather regional, and their production has to continue for their effects to be present. Their effects are also complex because some reflect the sun and cause cooling, some (carbonaceous) are dark and absorb the sun’s rays, and many become involved in clouds and affect the brightness, lifetime and disposition of clouds; in general, they cause a cooling effect.
“In contrast, even if we stopped emitting carbon dioxide into the atmosphere today, the elevated concentrations already established would persist for some time, thus underscoring the need for urgent reductions in carbon dioxide emissions. Hence, changes in atmospheric composition, and particularly the increase in carbon dioxide concentrations, enhance the greenhouse effect, although with important regional effects from aerosol particulates.”
2018 Ludwick Lecture — Dr. Kevin E. Trenberth, a distinguished senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research (NCAR)