Rothenberg D.

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Rothenberg
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D.
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  • Article
    Desert dust and anthropogenic aerosol interactions in the Community Climate System Model coupled-carbon-climate model
    (Copernicus Publications on behalf of the European Geosciences Union, 2011-02-15) Mahowald, Natalie M. ; Lindsay, Keith ; Rothenberg, D. ; Doney, Scott C. ; Moore, J. Keith ; Thornton, Peter E. ; Randerson, James T. ; Jones, C. D.
    Coupled-carbon-climate simulations are an essential tool for predicting the impact of human activity onto the climate and biogeochemistry. Here we incorporate prognostic desert dust and anthropogenic aerosols into the CCSM3.1 coupled carbon-climate model and explore the resulting interactions with climate and biogeochemical dynamics through a series of transient anthropogenic simulations (20th and 21st centuries) and sensitivity studies. The inclusion of prognostic aerosols into this model has a small net global cooling effect on climate but does not significantly impact the globally averaged carbon cycle; we argue that this is likely to be because the CCSM3.1 model has a small climate feedback onto the carbon cycle. We propose a mechanism for including desert dust and anthropogenic aerosols into a simple carbon-climate feedback analysis to explain the results of our and previous studies. Inclusion of aerosols has statistically significant impacts on regional climate and biogeochemistry, in particular through the effects on the ocean nitrogen cycle and primary productivity of altered iron inputs from desert dust deposition.
  • Article
    Observed 20th century desert dust variability : impact on climate and biogeochemistry
    (Copernicus Publications on behalf of the European Geosciences Union, 2010-11-19) Mahowald, Natalie M. ; Kloster, S. ; Engelstaedter, S. ; Moore, J. Keith ; Mukhopadhyay, S. ; McConnell, Joseph R. ; Albani, S. ; Doney, Scott C. ; Bhattacharya, A. ; Curran, M. A. J. ; Flanner, M. G. ; Hoffman, Forrest M. ; Lawrence, David M. ; Lindsay, Keith ; Mayewski, P. A. ; Neff, Jason C. ; Rothenberg, D. ; Thomas, E. ; Thornton, Peter E. ; Zender, Charles S.
    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.