Abstract:

Climate change is one of the most pressing challenges of our time, requiring accurate predictions to guide effective mitigation and adaptation strategies. Central to this effort is the need to estimate and better understand the physical mechanisms behind effective radiative forcing (ERF) from anthropogenic activities. ERF encompasses both the instantaneous radiative forcing from external forcing agents, such as greenhouse gases and aerosols, and the subsequent radiative adjustments, particularly those involving cloud changes. A major and persistent source of uncertainty in ERF estimates is anthropogenic aerosols, especially absorbing aerosols.

In this paper, we present a hierarchy of convective-permitting simulations to investigate ERF and cloud adjustments to absorbing aerosols. This first-of-its-kind model hierarchy spans small-domain simulations (capturing local responses), large-domain simulations (representing convective aggregation and large-scale tropical circulation), and mock Walker simulations (accounting for geographically oriented, sea surface temperature gradient-driven circulation). Our results demonstrate that ERF is primarily driven by cloud adjustments and that the baseline cloud regime distribution plays a crucial role in determining ERF. Specifically, as the simulation scale shifts from small-domain to large-domain and to mock Walker setup, the baseline cloud regime transitions from ice-dominated to shallow-cloud-dominated. Since shallow clouds are more susceptible to absorbing aerosol perturbations, cloud adjustments—and consequently ERF—increase across this hierarchy, from small to large to mock Walker simulations.