Atmos. Chem. Phys. Discuss., 10, 12585-12628, 2010
www.atmos-chem-phys-discuss.net/10/12585/2010/
doi:10.5194/acpd-10-12585-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Observed 20th century desert dust variability: impact on climate and biogeochemistry
N. M. Mahowald1, S. Kloster1, S. Engelstaedter1, J. K. Moore2, S. Mukhopadhyay3, J. R. McConnell4, S. Albani1, S. C. Doney5, A. Bhattacharya3, M. A. J. Curran6, M. G. Flanner7, F. M. Hoffman8, D. M. Lawrence9, K. Lindsay9, P. A. Mayewski10, J. Neff11, D. Rothenberg1, E. Thomas12, P. E. Thornton7, and C. S. Zender2
1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, 14853, USA
2Department of Earth System Science, University of California, Irvine, Irvine, CA, 92697, USA
3Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, 02138, USA
4Division of Hydrologic Sciences, Desert Research Institute, Reno, NV, 89512, USA
5Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA02543, USA
6Australian Antarctic Division, Hobart, Tasmania, 7001, Australia
7Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, 48109, USA
8Computational Earth Sciences Group, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
9Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, 80307, USA
10Climate Change Institute, University of Maine, Orono, ME, 04469, USA
11Geosciences Department and Environmental Studies Program, University of Colorado, Boulder, CO, 80301, USA
12British Antarctic Survey, Cambridge, CB3 0ET, UK

Abstract. Desert dust perturbs climate by interacting with incoming solar and outgoing long wave radiation, thereby changing precipitation and temperature, in addition to modifying ocean and land biogeochemistry. While we know that desert dust is sensitive to perturbations in climate and human land use, previous studies have been unable to determine whether humans were in the net increasing or decreasing desert dust. Here we present observational estimates of desert dust based on paleodata proxies showing a doubling of desert dust during the 20th century over much, but not all the globe. Large uncertainties remain in estimates of desert dust variability over 20th century due to limited data. Using these observational estimates of desert dust change in combination with ocean, atmosphere and land models, we calculate the net radiative effect of these observed changes (top of atmosphere) over the 20th century to be −0.14±0.11 W/m2 (1990–1999 vs. 1905–1914). The estimated radiative change due to aerosols is especially strong between the dusty 1980–1989 and the less dusty 1955–1964 time periods (−0.57±0.46 W/m2), which model simulations suggest may have reduced the rate of temperature increase between these time periods by 0.11 °C. Model simulations also indicate strong regional shifts in precipitation and temperature from the desert dust changes, causing 6 ppm (12 Pg C) reduction in model carbon uptake by the terrestrial biosphere over the 20th century. Desert dust carries iron, an important micronutrient for ocean biogeochemistry that can modulate ocean carbon storage; here we show that dust deposition trends increase ocean productivity by an estimated 6% over the 20th century, drawing down an additional 4 ppm (8 Pg C) of carbon dioxide into the oceans. Thus, perturbations to desert dust over the 20th century inferred from observations are potentially important for climate and biogeochemistry, and our understanding of these changes and their impacts should continue to be refined.

Citation: Mahowald, N. M., Kloster, S., Engelstaedter, S., Moore, J. K., Mukhopadhyay, S., McConnell, J. R., Albani, S., Doney, S. C., Bhattacharya, A., Curran, 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.: Observed 20th century desert dust variability: impact on climate and biogeochemistry, Atmos. Chem. Phys. Discuss., 10, 12585-12628, doi:10.5194/acpd-10-12585-2010, 2010.
 
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