4.6 Article

Efficacy of Climate Forcings in PDRMIP Models

Journal

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
Volume 124, Issue 23, Pages 12824-12844

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2019JD030581

Keywords

Efficacy; Climate Sensitivity; Radiative Forcing; Surface temperature; PDRMIP

Funding

  1. Natural Environment Research Council [NE/N006038/1, NE/K500872/1, NE/J022624/1, NE/L01355X/1, NE/P013406/1]
  2. European Union [820829]
  3. NERC [NE/M018199/1]
  4. Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme [GA01101]
  5. Research Council of Norway, through the grant NAPEX [229778]
  6. NASA GISS
  7. NEC SX-ACE supercomputer system of the National Institute for Environmental Studies, Japan
  8. Environmental Research and Technology Development Fund of the Ministry of Environment, Japan [S-12-3]
  9. JSPS KAKENHI [JP15H01728, JP15K12190]
  10. Grantham Institute at Imperial College
  11. Norwegian Research Council through the project EVA [229771]
  12. Norwegian Research Council through the project EarthClim [207711/E10]
  13. Norwegian Research Council through the project NOTUR [nn2345k]
  14. Norwegian Research Council through the project NorStore [ns2345k]
  15. European Research Council project RECAP under the European Union's Horizon 2020 Research and Innovation Programme [724602]
  16. NERC [NE/M018199/1, NE/J022624/1, NE/L01355X/1, NE/N006038/1, NE/P013406/1] Funding Source: UKRI

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Quantifying the efficacy of different climate forcings is important for understanding the real-world climate sensitivity. This study presents a systematic multimodel analysis of different climate driver efficacies using simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP). Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near-surface air temperature (GSAT) change. Efficacies are closest to one when ERF is computed using fixed sea surface temperature experiments and adjusted for land surface temperature changes using radiative kernels. Multimodel mean efficacies based on ERF are close to one for global perturbations of methane, sulfate, black carbon, and insolation, but there is notable intermodel spread. We do not find robust evidence that the geographic location of sulfate aerosol affects its efficacy. GSAT is found to respond more slowly to aerosol forcing than CO2 in the early stages of simulations. Despite these differences, we find that there is no evidence for an efficacy effect on historical GSAT trend estimates based on simulations with an impulse response model, nor on the resulting estimates of climate sensitivity derived from the historical period. However, the considerable intermodel spread in the computed efficacies means that we cannot rule out an efficacy-induced bias of +/- 0.4 K in equilibrium climate sensitivity to CO2 doubling when estimated using the historical GSAT trend.

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