Climate response to dust N. Mahowald, M. Yoshioka, D. Muhs, W. Collins, A. Conley, C. Zender, D. Fillmore, D. Coleman, P. Rasch

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Climate response to dust

  • N. Mahowald, M. Yoshioka, D. Muhs, W. Collins, A. Conley, C. Zender, D. Fillmore, D. Coleman, P. Rasch

Desert dust/mineral aerosols

  • Soil particles suspended in area

  • Source:

    • Unvegetated, dry soils with strong winds
  • Removal

    • Dry deposition, especially gravitation settling
    • Wet deposition, during precipitation
  • Model the sources, transport and deposition processes in 3-dimensional model (offline transport model: MATCH/NCEP or NCAR Community Atmospheric Model (CAM3) from the Community Climate System Model (CCSM3))

  • Papers available at

Sensitivity study (Yoshioka et al., in press)

  • Using CAM3 and slab ocean model

  • AMIP runs (SST impacts)

  • Vegetation changes (force model to change similar to estimated changes 1960s to 1990s)

  • Green house gas changes (2x co2 SOM runs)

  • Dust changes (with and without dust direct radiative forcing)

    • Only include direct radiative effects (ignoring CCN or IN interactions, which may be important)
    • Can’t get dust signal with amip and vegetation changes—need to force model to capture dust change at barbados
      • Model error
      • Land use source of dust
      • Vegetation change source of dust

Climate response to dust under different climates

How robust is this response?

  • Physical parameterizations or physical biases will impact our simulation of dust (or x variable we are interested in).

  • How does this impact our precipitation sensitivity?

  • Shift in precip due to dust radiative forcing is not sensitive to climate in our model (Mahowald et al., 2006)

  • Response is sensitive to single scattering Albedo (Miller et al., 2004; other papers)

    • Radiative properties of dust are not well established
      • Dust absorbs and scatters in long AND short wave
      • NOT spherical particles!

Smaller scale interactions

  • Dust and easterly waves

    • 20-40% of dust is generated and transported associated with easterly waves (Jones et al., 2003; using NCEP and NCEP/MATCH)
    • Easterly waves maybe enhanced by dust (Jones et al., 2004 NCEP/MATCH; Jones et al in prep (CAM3 T85)
  • Dust and hurricanes

    • Dust cools surface and suppresses precip in our model, some observation studies….(Yoshioka et al., in press, Wong and Dessler, Evans et al., in prep)…


  • In this set of model simulations:

  • SSTs are responsible for 50% of the Sahel signal (pretty robust across models)

  • Vegetation NS (different models show different results)

  • Dust responsible for up to 30% of Sahel drought signal in this model (consistent with one existing study? Need more models!)

    • Dust could be ‘natural’ or anthropogenic (Mahowald et al., 2002; Prospero and Lamb, 2003; Mahowalld and Luo, 2003; Tegen et al., 2004; Mahowald et al., 2004)
  • GHG in this model lead to higher precip—not robust result

  • Dust potentially an important feedback factor that should be better explored.

  • Not discussed here at length, but should not be ignored:

  • Anthropogenic changes in ‘natural’ aerosol are potentially large and should not be ignored

    • from direct perturbation of land (land use), climate change or carbon dioxide fertilization of plants
  • our estimates: (Mahowald et al., 2006; Mahowald and Luo, 2003)

    • PreindustrialI to present (-0.1 to 0.30C)
    • Present to future (doubled CO2) is about ~+0.06C
  • Dust changes could also be driving changes in ocean biogeochemistry and carbon dioxide fluxes (Mahowald et al., 2006; Moore et al., 2006)

Dust response to climate

Compare model changes to obs

  • Can’t distinguish preindustrial from current (Mahowald and Luo, 2003; Mahowald et al. 2006.

  • Compare against all available data in current climate. Dust deposition records for last glacial maximum.

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