Explaining Forcing Efficacy With Pattern Effect and State Dependence

The magnitude of global surface temperature change in response to unit radiative forcing depends on the type and magnitude of forcing agent-a concept known as a forcing efficacy. However, the mechanisms behind the forcing efficacy are still unclear. In this study, we perform a set of simulations using CESM1 to calculate the efficacy of 10 different forcing agents defined in terms of fixed-SST effective radiative forcing, and then use a Green's function approach to show that each forcing efficacy can be largely understood in terms of the radiative feedbacks associated with the different surface temperature patterns induced by the forcing agents (a pattern effect). We also quantify how the state dependence of feedbacks on global mean surface temperature anomalies impacts forcing efficacies. The results show that the forcing efficacy can be well reconstructed with a combination of pattern effect and state dependence.

Automated summary

In this study, simulations are conducted using CESM1 to calculate the forcing efficacy of 10 different forcing agents. The results show that the efficacy of each forcing agent can be largely explained in terms of the radiative feedbacks associated with the different surface temperature patterns induced by the forcing agents. The study also quantifies how the state dependence of feedbacks on global mean surface temperature anomalies impacts forcing efficacies.