Rapid Adjustments Cause Weak Surface Temperature Response to Increased Black Carbon Concentrations

Abstract

We investigate the climate response to increased concentrations of black carbon (BC), as part of the Precipitation Driver Response Model Intercomparison Project (PDRMIP). A tenfold increase in BC is simulated by nine global coupled‐climate models, producing a model median effective radiative forcing of 0.82 (ranging from 0.41 to 2.91) W m−2, and a warming of 0.67 (0.16 to 1.66) K globally and 1.24 (0.26 to 4.31) K in the Arctic. A strong positive instantaneous radiative forcing (median of 2.10 W m−2 based on five of the models) is countered by negative rapid adjustments (−0.64 W m−2 for the same five models), which dampen the total surface temperature signal. Unlike other drivers of climate change, the response of temperature and cloud profiles to the BC forcing is dominated by rapid adjustments. Low‐level cloud amounts increase for all models, while higher‐level clouds are diminished. The rapid temperature response is particularly strong above 400 hPa, where increased atmospheric stabilization and reduced cloud cover contrast the response pattern of the other drivers. In conclusion, we find that this substantial increase in BC concentrations does have considerable impacts on important aspects of the climate system. However, some of these effects tend to offset one another, leaving a relatively small median global warming of 0.47 K per W m−2—about 20% lower than the response to a doubling of CO2. Translating the tenfold increase in BC to the present‐day impact of anthropogenic BC (given the emissions used in this work) would leave a warming of merely 0.07 K.

Radiative Effects of Residential Sector Emissions in China: Sensitivity to Uncertainty in Black Carbon Emissions

“…The semidirect forcing tends to only be positive over limited continental regions, with the global net effect often negative and therefore acting counter to the positive direct radiative forcing (Stjern et al, 2017;Y. The semidirect forcing tends to only be positive over limited continental regions, with the global net effect often negative and therefore acting counter to the positive direct radiative forcing (Stjern et al, 2017;Y.…”

“…The semidirect forcing tends to only be positive over limited continental regions, with the global net effect often negative and therefore acting counter to the positive direct radiative forcing (Stjern et al, 2017;Y. The strength of the semidirect effect is also highly variable between models (Stjern et al, 2017) and nonlinearly dependent on the magnitude of BC emissions (Y. The strength of the semidirect effect is also highly variable between models (Stjern et al, 2017) and nonlinearly dependent on the magnitude of BC emissions (Y.…”

Dynamical response of Mediterranean precipitation to greenhouse gases and aerosols

“…Hence this study focuses on aspects of the response that appear to be less sensitive to those interactions as they are relatively robust across the models (despite some emission-driven models using interactive aerosols while others used climatological fields). Many PDRMIP studies have taken this approach Myhre et al, 2017;Stjern et al, 2017;Liu et al, 2018;Richardson et al, 2018), though further work with models incorporating more realistic aerosol-cloud in-teractions would of course be valuable in determining the veracity of all conclusions from the project.…”

Arctic Amplification Response to Individual Climate Drivers

“…The Precipitation Driver Response Model Intercomparison Project (PDRMIP) (Myhre et al, ) provides a unique data set that allows for investigations into climate responses to separate and clearly defined climate drivers, such as greenhouse gases or aerosols, in a multimodel framework. This has led the way for several studies that have investigated various aspects of climate driver‐response relationships from a global perspective (Liu et al, ; Samset et al, ; Samset et al, ; Stjern et al, ). Here we use the PDRMIP data set to analyze the climate response in the Arctic (defined as the region north of 60°N).…”