Do Soot Particle Effects on Clouds Contribute to Climate Cooling?


Soot particles emitted from incomplete combustion of fossil fuels and biofuels warm the atmosphere where they are suspended. However, their contribution to cloud brightening may cause a comparable cooling effect. In a recently published study, partially supported by DOE, six modeling groups performed three soot-reduction experiments and reported the effects on clouds. Pollution particles may contribute a large cooling effect by increasing the number of cloud droplets, which brighten the clouds. In the model experiments, reductions in soot from burning of wood and other biofuels, which are relatively large and hygroscopic particles, usually resulted in cloud reduction and a positive radiative flux (warming effect). However, if the smaller, less hygroscopic, fossil fuel soot was reduced, the clouds actually increased for some of the models due to a resulting shift in the overall aerosol population toward larger and more hygroscopic particles. The study reinforces the complexity and uncertainty of aerosol-climate effects, and reinforces the need for further model experiments and field studies to validate how aerosol species mix and interact with clouds.


Koch, D., Y. Balkanski, S. E. Bauer, R. C. Easter, S. Ferrachat, S. J. Ghan, C. Hoose, T. Iversen, A. Kirkevåg, J. E. Kristjansson, X. Liu, U. Lohmann, S. Menon, J. Quaas, M. Schulz, Ø. Seland, T. Takemura, and N. Yan. 2011. “Soot Microphysical Effects on Liquid Clouds: A Multi-Model Investigation,” Atmospheric Chemistry and Physics 11, 1051–1064, doi:10.5194/acp-11-1051-2011.