Climate Dynamics Group
at the University of California, Santa Cruz

• Nicole Feldl
• Jing Feng
• David Paynter

Reliable estimates of climate sensitivity require understanding how patterns of surface temperature change influence the global radiative feedback. Here we present a theoretical basis for this pattern effect as it relates to the longwave clear sky feedback. A moist adiabatic feedback framework is developed that partitions the feedback into components associated with locally determined moist adiabatic processes and components associated with deviations therefrom, such as due to nonlocal influences and relative humidity changes. Applying this feedback framework to simulations forced by transient and equilibrium patterns of sea surface temperature change reveals that the pattern effect is driven by different physical processes in different geographic regions. In the subtropics, the more stabilizing feedback under transient climate change is explained by a more negative relative humidity feedback. Over the Southern Ocean, the less stabilizing feedback under transient climate change occurs due to the muted surface warming there, which promotes a weak surface temperature feedback; furthermore, for an idealized pattern of change in which the transient sea surface temperature change is uniformly increased but retains the same structure, the pattern effect essentially disappears. The moist adiabatic feedback framework demonstrates that the evolving zonal-mean longwave clear sky feedback—towards stabilization at high latitudes and destabilization at low latitudes, as the climate approaches equilibrium—is controlled by processes, specifically surface temperature and relative humidity feedbacks, not isolated by conventional feedback analysis. In the global mean, the destabilization effect proves larger, receiving additional contributions from small but geographically extensive differences in the fixed-relative humidity atmospheric temperature feedback.