Understanding the Climate Response to Different Vertical Patterns of Radiative Forcing

Abstract The dependence of climate response on the vertical structure of radiative forcing is studied using a set of idealized experiments, with horizontally uniform and vertically confined forcings. We find for a given effective forcing magnitude, higher‐altitude forcing causes a smaller global warming, owing to more negative cloud feedback. We present novel evidence relating this altitude dependence to sea‐surface temperature patterns and tropospheric static stability. The imposed instantaneous forcings are horizontally uniform, but higher‐altitude forcings more effectively suppress convection in the tropical warm pool, producing a more positive effective (adjusted) surface forcing in that region. This gives rise, during the subsequent climate change, to greater warming contrast between the warm pool and rest of the globe, and hence to increase in low cloud amount. Our results show that to achieve accurate climate projections under anthropogenic forcings, it is important to correctly represent the vertical structures of the applied radiative forcing.