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Title: Linearity of Climate Response to Increases in Black Carbon Aerosols

Abstract

The impact of absorbing aerosols on global climate are not completely understood. Here, we present results of idealized experiments conducted with the Community Atmosphere Model (CAM4) coupled to a slab ocean model (CAM4-SOM) to simulate the climate response to increases in tropospheric black carbon aerosols (BC) by direct and semi-direct effects. CAM4-SOM was forced with 0, 1x, 2x, 5x and 10x an estimate of the present day concentration of BC while maintaining their estimated present day global spatial and vertical distribution. The top of the atmosphere (TOA) radiative forcing of BC in these experiments is positive (warming) and increases linearly as the BC burden increases. The total semi-direct effect for the 1x experiment is positive but becomes increasingly negative for higher BC concentrations. The global average surface temperature response is found to be a linear function of the TOA radiative forcing. The climate sensitivity to BC from these experiments is estimated to be 0.42 K $$ W^{-1} m^{2}$$ when the semi-direct effects are accounted for and 0.22 K $$ W^{-1} m^{2}$$ with only the direct effects considered. Global average precipitation decreases linearly as BC increases, with a precipitation sensitivity to atmospheric absorption of 0.4 $$\%$$ $$W^{-1}m^{2}$$ . The hemispheric asymmetrymore » of BC also causes an increase in southward cross-equatorial heat transport and a resulting northward shift of the inter-tropical convergence zone in the simulations at a rate of 4$$^{\circ}$$N $$ PW^{-1}$$. Global average mid- and high-level clouds decrease, whereas the low-level clouds increase linearly with BC. The increase in marine stratocumulus cloud fraction over the south tropical Atlantic is caused by increased BC-induced diabatic heating of the free troposphere.« less

Authors:
 [1];  [1];  [1];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. National Center for Atmospheric Research (NCAR), Boulder, CO (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1092284
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 26; Journal Issue: 20; Journal ID: ISSN 0894-8755
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Mahajan, Salil, Evans, Katherine J., Hack, James J., and Truesdale, John. Linearity of Climate Response to Increases in Black Carbon Aerosols. United States: N. p., 2013. Web. doi:10.1175/JCLI-D-12-00715.1.
Mahajan, Salil, Evans, Katherine J., Hack, James J., & Truesdale, John. Linearity of Climate Response to Increases in Black Carbon Aerosols. United States. https://doi.org/10.1175/JCLI-D-12-00715.1
Mahajan, Salil, Evans, Katherine J., Hack, James J., and Truesdale, John. Fri . "Linearity of Climate Response to Increases in Black Carbon Aerosols". United States. https://doi.org/10.1175/JCLI-D-12-00715.1.
@article{osti_1092284,
title = {Linearity of Climate Response to Increases in Black Carbon Aerosols},
author = {Mahajan, Salil and Evans, Katherine J. and Hack, James J. and Truesdale, John},
abstractNote = {The impact of absorbing aerosols on global climate are not completely understood. Here, we present results of idealized experiments conducted with the Community Atmosphere Model (CAM4) coupled to a slab ocean model (CAM4-SOM) to simulate the climate response to increases in tropospheric black carbon aerosols (BC) by direct and semi-direct effects. CAM4-SOM was forced with 0, 1x, 2x, 5x and 10x an estimate of the present day concentration of BC while maintaining their estimated present day global spatial and vertical distribution. The top of the atmosphere (TOA) radiative forcing of BC in these experiments is positive (warming) and increases linearly as the BC burden increases. The total semi-direct effect for the 1x experiment is positive but becomes increasingly negative for higher BC concentrations. The global average surface temperature response is found to be a linear function of the TOA radiative forcing. The climate sensitivity to BC from these experiments is estimated to be 0.42 K $ W^{-1} m^{2}$ when the semi-direct effects are accounted for and 0.22 K $ W^{-1} m^{2}$ with only the direct effects considered. Global average precipitation decreases linearly as BC increases, with a precipitation sensitivity to atmospheric absorption of 0.4 $\%$ $W^{-1}m^{2}$ . The hemispheric asymmetry of BC also causes an increase in southward cross-equatorial heat transport and a resulting northward shift of the inter-tropical convergence zone in the simulations at a rate of 4$^{\circ}$N $ PW^{-1}$. Global average mid- and high-level clouds decrease, whereas the low-level clouds increase linearly with BC. The increase in marine stratocumulus cloud fraction over the south tropical Atlantic is caused by increased BC-induced diabatic heating of the free troposphere.},
doi = {10.1175/JCLI-D-12-00715.1},
url = {https://www.osti.gov/biblio/1092284}, journal = {Journal of Climate},
issn = {0894-8755},
number = 20,
volume = 26,
place = {United States},
year = {2013},
month = {4}
}