The Web of Life (18-8) Dust continued


Dust from north Africa and the Arabian Peninsula is lofted toward India. The dust absorbs sunshine, warming the air, and strengthening the winds that blow from the Indian Ocean, carrying moisture eastward. Thus, dust affects the intensity of summer monsoon rainfall in India.

The tropics and mid-latitude arid regions are not the only dust source, though they are the major ones. Dust generated in the higher latitudes is not confined to arid regions. Because of strong seasonal winds, humid areas, even near glacial regions, generate dust.

Airborne dust fashions fickle effects. Do-nothing dust for millennia may suddenly start to modulate the global climate: absorbing warmth from the Sun and rays reflected off Earth’s surface, and thus warming the atmosphere. Dust with soot absorbs even more heat.

Dust can have the opposite influence: cooling by reflection rather than absorbing heat. The effect depends upon dust’s chemical composition and size, as well as the wavelength of light that hits it. Generally, dust tends to reflect shortwave solar radiation, while absorbing the longer-wave bounce-back from the Earth.

Dust over darker areas, notably the oceans, has a cooling effect, by reflecting light that would otherwise be absorbed at the surface. Dust on ice or snow darkens it, willing warming.

Moisture in the air must attach to particulates to form droplets that lead to rain, or, in colder conditions, hail and snow. Aerial bacteria play this particulate part, as does dust. Exactly how these particulates affect precipitation varies depending upon a variety of factors, including the characteristics of the dust.

Airborne dust has doubled in the past century. While it generally has a cooling effect in the atmosphere, there are too many variables to characterize its temperate effects.

Large areas of the ocean are rich in nitrogen and phosphorus. An iron shortage limits what would otherwise engender massive plankton blooms. African dust has a high iron content.

Not only does dust craft the global climate, but the climate claims a toll on dust. Just as dust modulates climate variability, dust is dependent upon climate.

If climate change affects wind velocity and rainfall, it can have an immense impact. Dust is extremely sensitive to small changes in wind and rain. It’s the ultimate feedback loop. ~ Joseph Prospero