Climate Dynamics

, Volume 38, Issue 5, pp 897–911

Dependence of climate forcing and response on the altitude of black carbon aerosols

Authors

    • Department of Global EcologyCarnegie Institution
  • Long Cao
    • Department of Global EcologyCarnegie Institution
  • G. Bala
    • Divecha Center for Climate Change and Center for Atmospheric and Ocean SciencesIndian Institute of Science
  • Ken Caldeira
    • Department of Global EcologyCarnegie Institution
Article

DOI: 10.1007/s00382-011-1052-y

Cite this article as:
Ban-Weiss, G.A., Cao, L., Bala, G. et al. Clim Dyn (2012) 38: 897. doi:10.1007/s00382-011-1052-y

Abstract

Black carbon aerosols absorb solar radiation and decrease planetary albedo, and thus can contribute to climate warming. In this paper, the dependence of equilibrium climate response on the altitude of black carbon is explored using an atmospheric general circulation model coupled to a mixed layer ocean model. The simulations model aerosol direct and semi-direct effects, but not indirect effects. Aerosol concentrations are prescribed and not interactive. It is shown that climate response of black carbon is highly dependent on the altitude of the aerosol. As the altitude of black carbon increases, surface temperatures decrease; black carbon near the surface causes surface warming, whereas black carbon near the tropopause and in the stratosphere causes surface cooling. This cooling occurs despite increasing planetary absorption of sunlight (i.e. decreasing planetary albedo). We find that the trend in surface air temperature response versus the altitude of black carbon is consistent with our calculations of radiative forcing after the troposphere, stratosphere, and land surface have undergone rapid adjustment, calculated as “regressed” radiative forcing. The variation in climate response from black carbon at different altitudes occurs largely from different fast climate responses; temperature dependent feedbacks are not statistically distinguishable. Impacts of black carbon at various altitudes on the hydrological cycle are also discussed; black carbon in the lowest atmospheric layer increases precipitation despite reductions in solar radiation reaching the surface, whereas black carbon at higher altitudes decreases precipitation.

Keywords

Black carbon Aerosol Soot Climate change Global warming Altitude Fast response Climate sensitivity Feedback parameter

Supplementary material

382_2011_1052_MOESM1_ESM.pdf (410 kb)
Online Resource 1. Figure S1 Regressions of key climate variables versus changes in surface air temperature following the method of Gregory et al. (2004). Annual means of the first 20 years of the simulations are used in the regressions. To decrease uncertainty, we ran a total of three 20-year simulations for each case of increased black carbon. Thus the regressions are based on annual averages of the first 20 years of three ensemble members for each case. (PDF 409 kb)
382_2011_1052_MOESM2_ESM.pdf (34 kb)
Online Resource 2. Table S1 Numerical values of key climate variables for each simulation. All results presented represent global averages of the last 70 years of 100-year simulations. Altitudes given in the top row indicate the approximate altitude with additional black carbon in each simulation. Uncertainty is given by the standard error computed from 70 annual means using the Student t test. The standard error is corrected for autocorrelation (Zwiers and von Storch 1995). (PDF 33 kb)
382_2011_1052_MOESM3_ESM.tif (15.5 mb)
Online Resource 3. Figure S2 Changes in surface temperature, instantaneous forcing, adjusted forcing, fixed-SST radiative forcing, and regressed radiative forcing as reported in Table 2 of Hansen et al. (2005). Each simulation added black carbon aerosol to a different layer in the troposphere by increasing aerosol optical depth of that layer. (TIFF 15,890 kb)

Copyright information

© Springer-Verlag 2011