Background
Airborne dust is a major threat to the health of both people (Prospero, 2001) and coral polyps (Shinn et al., 2000), plus everything in between (Wilkening et al., 2000), carrying with it a vast array of pathogenic fungi, bacteria and viruses, as well as elements such as iron, which when introduced into people's lungs can rapidly produce a serious inflammatory response.  In discussing this vast array of biospheric health concerns, we have consistently suggested that atmospheric CO2 enrichment, which enhances plant water use efficiency and stimulates growth, would help to ameliorate these problems by enabling vegetation to (1) grow where it has been too dry for plants to gain a foothold in the past and (2) grow more abundantly where plants have previously provided only sparse ground cover, thereby producing a significant "greening" of arid and semi-arid lands and reducing the propensity for wind to disturb the soil surface and lift a portion of its fine particulates to heights where they can literally cross oceans and deposit their deadly travel companions on the opposite side of the world.

What was done
Engelstaedter et al. (2003) used dust storm frequency (DSF) data -- obtained from 2405 meteorological stations represented in the International Station Meteorological Climate Summary -- as a surrogate measure of dust emissions to explicitly test the assumption that vegetation is an important control of dust emission at the global scale.  To represent vegetation cover, they used two independent data sets: a satellite-derived distribution of actual vegetation types and a model-derived distribution of potential natural vegetation.

What was learned
In the words of the authors, "the highest DSFs are found in areas mapped by DeFries and Townshend (1994) as bare ground," while "moderate DSFs occur in regions with more vegetation, i.e., shrubs & bare ground, and lowest DSFs occur in grasslands, forests, and tundra," where ground cover is highest.  Hence, and as we have long implied, the authors conclude that "average DSF is inversely correlated with leaf area index (an index of vegetation density) and net primary productivity."

What it means
The authors' work establishes the reality of the scenario we describe in our reviews of the studies of Prospero (2001), Shinn et al. (2000) and Wilkening et al. (2000), whereby the ongoing rise in the air's CO2 content promotes the growth of vegetation on arid and semi-arid lands, which reduces the propensity for airborne dust and its associated pathogens and other harmful substances to be transported around the world by air currents.  Hence, this knowledge provides an additional and very important reason to allow the historical upward trajectory of the atmosphere's CO2 concentration to continue unabated.  It's good for our health ? and the health of the rest of the biosphere as well.

References
DeFries, R.S. and Townshend, J.R.G.  1994.  NDVI-derived land cover classification at a global scale.  International Journal of Remote Sensing 15: 3567-3586.

Prospero, J.M.  2001.  African dust in America.  Geotimes 46(11): 24-27.

Shinn, E.A., Smith, G.W., Prospero, J.M., Betzer, P., Hayes, M.L., Garrison, V. and Barber, R.T.  2000.  African dust and the demise of Caribbean coral reefs.  Geophysical Research Letters 27: 3029-3032.

Wilkening, K.E., Barrie, L.A. and Engle, M.  2000.  Trans-Pacific air pollution.  Science 290: 65-67.