World map showing multi-model mean efficacy (ERFsst) distribution in the five-times sulfate aerosol concentrations or emissions experiment
Multi-model mean efficacy (ERFsst) distribution—defined as the ratio of temperature change per unit radiative forcing relative to that due to carbon dioxide change—in the five-times sulfate aerosol concentrations or emissions experiment (5×SO4). Hatching shows where the multi-model mean is less than the inter-model standard deviation. Credit: Richardson et al. [2019], Figure 2d
Source: Journal of Geophysical Research: Atmospheres

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. [2019] 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. [2019]. Efficacy of climate forcings in PDRMIP models. Journal of Geophysical Research: Atmospheres, 124, 12824– 12844.  

—Minghua Zhang, Editor in Chief, JGR: Atmospheres

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