How does global surface temperature respond to different forcings, such as carbon dioxide or aerosols? Previous works have shown that the forcing efficacies of different agents can differ substantially and that their calculations are sensitive to the definition of the radiative forcings used.
By invoking a simple step-response model along with the derived multi-model mean response curves for different forcing agents, Richardson et al.  found that efficacies for major anthropogenic forcing agents is close to unity so that they should not strongly affect estimates of climate sensitivity derived from the historical period. In addition, the authors provide interesting plots showing spatial distribution of forcings and the responses to different forcings. These results are important for understanding historical simulations, constraining climate sensitivity from the historical record, projecting future climate change.
Citation: Richardson, T. B., Forster, P. M., Smith, C. J., Maycock, A. C., Wood, T., Andrews, T., et al. . Efficacy of climate forcings in PDRMIP models. Journal of Geophysical Research: Atmospheres, 124, 12824– 12844. https://doi.org/10.1029/2019JD030581
—Minghua Zhang, Editor in Chief, JGR: Atmospheres