The ongoing rise in the air's CO2 content could do much to reverse this trend.  At higher atmospheric CO2 concentrations, nearly all plants are more efficient at utilizing water (Morison, 1985).  Hence, as the air's CO2 content rises, the vegetation that rings the earth's deserts should be able to encroach upon them and more effectively protect their surfaces from the ravages of the wind, thereby reducing soil and carbon losses due to erosion.  Also, rising atmospheric CO2 concentrations should enhance the stability of surface soil crusts that are held together by lichens and/or algae (Tuba et al., 1998; Brostoff et al., 2002), which should also help to reduce the deleterious effects of wind erosion (Evans and Johansen, 1999).  In addition, many of the algal components of desert soil crusts are nitrogen-fixers (Evans and Belnap, 1999); and their CO2-enhanced presence should lead to more nitrogen being made available to other plants, which should accelerate the development of soil-protecting ecosystems even more.

The end result of all of these phenomena working together is greater carbon storage, both above- and below-ground, in what was previously little more than a source of dust for the rest of the world.  And therein lies one of the great unanticipated benefits of this CO2-induced greening of the globe's deserts: less airborne dust to spread havoc throughout the earth.

To help explain what we're talking about here, we refer to a recent article in American Scientist magazine entitled "The Global Transport of Dust," which was produced by four scientists with the U.S. Geological Survey (Griffin et al., 2002), one of them a geologist, one a microbiologist, one a marine biologist, and one a coral-reef ecologist.

The eclectic group of scientists begins their essay with a description of the magnitude of soil materials wafted about by the wind.  "By some estimates," they say, "as much as two billion metric tons of dust are lifted into the Earth's atmosphere every year."  And riding along on these particles are "pollutants such as herbicides and pesticides and a significant number of microorganisms - bacteria, viruses and fungi."  In fact, the scientists calculate there are easily enough bacteria thus moved about the planet each year "to form a microbial bridge between Earth and Jupiter."

But does dust from Africa and Asia really go that far?  Well, it may not traverse interplanetary space; but it does cross both the Atlantic and Pacific Oceans.  Griffin et al. report that dust storms originating in North Africa "routinely affect the air quality in Europe and the Middle East" and that millions of tons of African sediment "fall on the North Amazon Basin of South America every year."  Likewise, Prospero (2001) tells us that everyone in the United States living east of the Mississippi River is affected by dust of African origin.

Asian dust also travels immense distances.  In April of 2001, for example, Griffin et al. report that a large dust cloud that originated over the Gobi Desert of China "moved eastward across the globe, crossing Korea, Japan, the Pacific (in five days), North America (causing sporadic reports of poor air quality in the United States), the Atlantic Ocean and then Europe."

Many of the biological entities associated with the dust particles that are thus dispersed about the planet have serious consequences for plants, animals and humans.  Airborne fungi from Africa that frequently make their way to the Americas, for example, cause sugar cane rust, coffee rust and banana leaf spot.  Griffin et al. describe how the scourge of Caribbean sea fans - Aspergillus sydowii - "is also found in the Caribbean atmosphere during African dust events," noting that the region's "sea fans and other coral reef organisms have experienced a steady decline since the late 1970s," when worsening drought in Africa predisposed increasing amounts of soil there to wind erosion (Prospero, 2001).  The scientists also say they expect "future research will show that many other coral diseases are spread by dust from both Africa and Asia."

With respect to human health, Griffin et al. note that "African dust is reported to be a vector for the meningococcal meningitis pathogen Neisseria meningitis in sub-Saharan Africa," and that outbreaks of the disease "often follow localized or regional dust events, and these typically result in many fatalities."  They also report there has been a 17-fold increase in the incidence of asthma on the island of Barbados since 1973, "which corresponds to the period when the quantities of African dust in the region started to increase."

Because the dust clouds that reach the Americas from Africa and Asia have traveled such long distances, most of the larger particles they originally contained have generally fallen out of them along the way.  The particles that remain, therefore, are typically very small, so small, in fact, that Griffin et al. report that "once they are inhaled into the lungs they cannot be exhaled."  What makes this situation especially serious is that the tiny dust particles typically are heavily coated with iron; and a substantial fraction of that iron is released to the lung tissue when the particles are deposited there.  And iron, as Prospero notes, is "particularly efficient in producing an inflammatory response in the lungs."

In light of these incredible-but-true observations, it is clear that the slow but steady acceleration of carbon sequestration in the deserts of Africa and Asia, which is being provided by the ongoing rise in the air's CO2 content, is producing more than just local benefits.  Plants and animals far and wide, on land and in the sea, together with people everywhere, will ultimately benefit, if they are not already doing so, from the reduced airborne-dispersal of pathogens responsible for many debilitating diseases, as source-region soils become better protected against the erosive power of the wind.  And if natural carbon sequestration tendencies can bring about these ancillary benefits, so too can those of man.  Consequently, citizens involved in local carbon sequestration projects can take satisfaction from the fact that their efforts are having a positive impact on the global environment in more ways than one.  Even if rising concentrations of atmospheric CO2 have no substantial impact on the world's climate, for example, there are many other reasons to be involved in projects designed to enhance the productivity of the planet's managed and natural ecosystems, not the least of which is the reduction of airborne dust and its multiple negative impacts on biospheric health that result from greater vegetative coverage of the soil.

References
Brostoff, W.N., Sharifi, M.R. and Rundel, P.W.  2002.  Photosynthesis of cryptobiotic crusts in a seasonally inundated system of pans and dunes at Edwards Air Force Base, western Mojave Desert, California: laboratory studies.  Flora 197: 143-151.

Evans, R.D. and Belnap, J.  1999.  Long-term consequences of disturbance on nitrogen dynamics in an arid ecosystem.  Ecology 80: 150-160.

Evans, R.D. and Johansen, J.R.  1999.  Microbiotic crusts and ecosystem processes.  Critical Reviews in Plant Sciences 18: 183-225.

Griffin, D.W., Kellogg, C.A., Garrison, V.H. and Shinn, E.A.  2002.  The global transport of dust.  American Scientist 90: 228-235.

Morison, J.I.L.  1985.  Sensitivity of stomata and water use efficiency to high CO2.  Plant, Cell and Environment 8: 467-474.

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

Tuba, Z., Csintalan, Z., Szente, K., Nagy, Z. and Grace, J.  1998.  Carbon gains by desiccation-tolerant plants at elevated CO2.  Functional Ecology 12: 39-44.