We do, especially since Israeli scientists showed how the latter woes are joined in a nightmarish feedback loop.
Satellite view of dust blowing from North Africa across the Mediterranean, July 8, 2000. Courtesy NASA
They say dust storms in the Sahara Desert are interfering with rainfall, which would increase drought, reducing ground cover and causing more dust -- which would further interfere with rainfall.
The impact of dust is not academic, since the stuff blows in the wind for thousands of miles. These satellite images show African dust reaching the Western Hemisphere. Dust originating in China can block the view at California's Death Valley National Monument.
Evidence that dust inhibits rainfall comes from new research by Daniel Rosenfeld of The Hebrew University in Jerusalem. While dust helps rain droplets to form, he thinks Africa's deserts are supplying too much of a good thing. Due to thermodynamic equations beyond the ken of Why Filers (but doubtless within the ken of math whizzes Ken and Barbie), water vapor molecules can condense and form cloud droplets only on existing particles, primarily dust and smoke.
With so many condensation nuclei present in the dusty clouds, cloud droplets remained too small to merge into heavy drops that can fall as rain. Predictably, the dusty clouds produced less rain than the comparison clouds.
The chemistry of the particles also played a role, Rosenfeld told us by e-mail. "The size of the drops depends on the amount of water absorbing material in the dust particles." Although many dust particles were large, he adds, "the very small amount of water-absorbing substance in the dust particles made them conducive to creation of only small cloud droplets."
Because global rainfall is fixed and must balance global evaporation, Rosenfeld wrote us, "The reduction of rainfall in the polluted or dusty areas may cause excessive rainfall ... up to many thousands of kilometers away. Therefore, the dust, smoke and air pollution can cause more extremes, more droughts in some areas and more floods in other areas."
Barren deserts will continue to emit dust no matter what we do, Rosenfeld says. But air pollution, overgrazing and other destructive agricultural practices are all controllable, at least in theory. However, with the world economy booming, and Africa's surging population placing more pressure on fragile landscapes, we wouldn't bet on a reduction of dust and pollution any time soon.
What does language tell us about African history?
are 1 2 3 4
5 pages in this feature.
Bibliography | Credits | Feedback | Search