Rapid Adjustments Cause Weak Surface Temperature Response to Increased Black Carbon Concentrations. Issue 21 (6th November 2017)

• Record Type: Journal Article
• Authors: Stjern, Camilla Weum; Samset, Bjørn Hallvard; Myhre, Gunnar; Forster, Piers M.; Hodnebrog, Øivind; Andrews, Timothy; Boucher, Olivier; Faluvegi, Gregory; Iversen, Trond; Kasoar, Matthew; Kharin, Viatcheslav; Kirkevåg, Alf; Lamarque, Jean‐François; Olivié, Dirk; Richardson, Thomas; Shawki, Dilshad; Shindell, Drew; Smith, Christopher J.; Takemura, Toshihiko; Voulgarakis, Apostolos
• Is Part Of: Journal of geophysical research. Volume 122:Issue 21(2017)
• Page Start: 11, 462
• Page End: 11, 481
• Publication Date: 2017-11-06
• Subjects: black carbon -- rapid adjustments -- climate -- semidirect; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2017JD027326
• Languages: English
• ISSNs: 2169-897X

Abstract

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. Key Points: Countering climate responses result in low‐temperature change relative to the large instantaneous radiative forcing that the BC perturbation causes Regionally, BC can have considerable impact on precipitation The intermodel spread is in general large, and 2.5 times higher if emissions instead of fixed BC concentrations are used in the simulations