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Representations of Aeolian Dust in CMIP5 Climate Models

Paper Reviewed
Evan, A.T., Flamant, C., Fiedler, S. and Doherty, O. 2014. An analysis of aeolian dust in climate models. Geophysical Research Letters 41: 5996-6001.

In providing some background for their analysis of how well the most up-to-date CMIP5 climate models represent aeolian dust, Evan et al. (2014) write that "aeolian dust is a key aspect of the climate system," since "dust can modify the Earth's energy budget, provide long-range transport of nutrients, and influence land surface processes via erosion." However, they indicate that the representation of dust in state-of-the-art climate models has not been systematically evaluated," and they thus proceed to fill this important analytic void.

Focusing on observations related to dust emission and transport from northern Africa - which they say is the world's largest source of airborne dust, citing Washington et al. (2003) - the four researchers evaluated "African dust in 23 state-of-the-art global climate models used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change," and in doing so, they determined that "all models fail to reproduce basic aspects of dust emission and transport over the second half of the twentieth century," and that they also "systematically underestimate dust emission, transport, and optical depth," while "year-to-year changes in these properties bear little resemblance to observations."

In light of their several findings, Evan et al. come to the conclusion that "there is no reason to assume that the projections of dust emission and concentration for the 21st century have any validity." And they add that their results "also cast doubt on the representation of other features of coupled Earth systems that are affected by aeolian dust, including regional land and ocean surface temperatures (Evan et al., 2009), precipitation and cloud processes (Kaufman et al., 2005; Yoshioka et al., 2007), coupled equatorial processes (Evan et al., 2011), and terrestrial (Das et al., 2013) and oceanic biogeochemistry (Mahowald et al., 2010)."

Given this terrible indictment of the models, one wonders how in the world the IPCC and others have so long claimed such certainty with respect to the models' future projections of climate.

References
Das, H., Evan, A.T. and Lawrence, D. 2013. Contributions of long-distance dust transport to atmospheric P inputs in the Yucatan Peninsula. Global Biogeochemical Cycles 27: 167-175.

Evan, A.T., Foltz, G.R., Zhang, D. and Vimont, D.J. 2011. Influence of African dust on ocean-atmosphere variability in the tropical Atlantic. Nature Geoscience 4: 762-765.

Evan, A.T., Vimont, D.J., Bennartz, R., Kossin,J.P. and Heidinger, A.K. 2009. The role of aerosols in the evolution of tropical North Atlantic Ocean temperature. Science 324: 778-781.

Kaufman, Y.J., Koren, I., Remer, L.A., Rosenfeld, D. and Rudich, Y. 2005. The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean. Proceedings of the National Academy of Sciences USA 102: 11,207-11,212.

Mahowald, N.M., Kloster, S., Engelstaedter, S., Moore, J.K., Mukhopadhyay, S., McConnell, J.R., Albani, S., Doney,S.C., Bhattacharya, A., Curan, M.A.J., Flanner, M.G., Hoffman, F.M., Lawrence, D.M., Lindsay, K., Mayewski, P.A., Neff, J., Rothenberg, D., Thomas, E., Thornton, P.E. and Zender, C.S. 2010. Observed 20th century desert dust variability: Impact on climate and biogeochemistry. Atmospheric Chemistry and Physics 10: 10,875-10,893.

Washington, R., Todd, M., Middleton,N.J. and Goudie, A.S. 2003. Dust-storm source areas determined by the total ozone monitoring spectrometer and surface observations. Annals of the Association of American Geographers 93: 297-313.

Yoshioka, M., Mahowald, N.M., Conley, A.J., Collins, W.D., Fillmore, D.W., Zender, C.S. and Coleman, D.B. 2007. Impact of desert dust radiative forcing on Sahel precipitation: Relative importance of dust compared to sea surface temperature variations, vegetation changes, and greenhouse gas warming. Journal of Climate 20: 1445-1467.

Posted 3 February 2015