Articles | Volume 10, issue 22
Atmos. Chem. Phys., 10, 10875–10893, 2010
Atmos. Chem. Phys., 10, 10875–10893, 2010

  19 Nov 2010

19 Nov 2010

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. Albani1,5, S. C. Doney6, A. Bhattacharya3, M. A. J. Curran7,8, M. G. Flanner9, F. M. Hoffman10, D. M. Lawrence11, K. Lindsay11, P. A. Mayewski12, J. Neff13, D. Rothenberg1, E. Thomas14, P. E. Thornton9, and C. S. Zender2 N. M. Mahowald et al.
  • 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
  • 5Department of Environmental Sciences, University of Milano-Bicocca, Milano, 20126, Italy
  • 6Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543, USA
  • 7Australian Antarctic Division, Kingston, Tasmania, 7050, Australia
  • 8Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania, 7001, Australia
  • 9Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, 48109, USA
  • 10Computational Earth Sciences Group, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
  • 11Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80307, USA
  • 12Climate Change Institute, University of Maine, Orono, ME, 04469, USA
  • 13Geosciences Department and Environmental Studies Program, University of Colorado, Boulder, CO, 80301, USA
  • 14British Antarctic Survey, Cambridge, CB3 0ET, UK

Abstract. Desert dust perturbs climate by directly and indirectly 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 increasing or decreasing desert dust in the global average. 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 dust is especially strong between the heavily loaded 1980–1989 and the less heavily loaded 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 desert dust changes, causing 6 ppm (12 PgC) 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 PgC) 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.

Final-revised paper