Dust
Dust is the ultimate feedback loop. ~ American meteorologist Joseph Prospero
Dust storms arise when hot air over the desert destabilizes the lower atmosphere, whipping up strong winds which send massive amounts of dust, sand, and soil across oceans and continents. 2 billion tonnes of dust move around the globe every year, borne as atmospheric tides. Riding in these clouds are all sorts of microbes and aerosol pollutants.
More than half of the world’s dust flows from African deserts and dry lands. Much of it is carried on westward trade winds across the Atlantic to the Americas. The Middle East and Europe get a goodly share of African dust as well.
Dust from Africa has skyrocketed since the mid-1800s, when commercial agriculture took root in the Sahel region, south of the Sahara desert and north of the Sudanian savanna. Inept plowing practices has hundreds of millions of tonnes of valuable topsoil blow away. Other regions of Africa have contributed their dirt to the wind as economic development got underway.
A terrestrial fungus and infectious bacteria have devastated Caribbean sea fan coral in the past few decades. The pathogens were delivered to the Caribbean Sea from the plains of Africa.
The fungus responsible for sugarcane rust explosively spread across Caribbean fields in the late 1970s and early 1980s, decimating the sugar industry. The rust came on dust from Cameroon, in west Africa.
British livestock suffered dozens of outbreaks of foot-and-mouth disease between the 1950s and 1980s. The viruses doing the damage dropped from the sky, delivered from Africa.
Seasonal asthma attacks in Barbados, off the coast of South America, correspond with the arrival of African dust clouds.
China
Dust from China lands in Hawaii and western North America. Greenland is also landfall for Asian dust.
Nearly 20% of China is desert. For decades, China’s deserts have been spreading every year by ~340,000 hectares: mostly in northern China, where drought is worsening. In 2017, China had 5.5 million hectares more desert than it did in 1975.
Thanks to rapid urbanization, deforestation, and climate change, northern China is blanketed in dust storms annually. A half century ago, such storms happened every 7–8 years.
China’s dust storms typically occur during the spring, as strong winds send sand from the Gobi Desert over northern China and into the Korean peninsula. Dust storms typically hit after the region has been afflicted by high wintertime smog, which is precipitated by pollutants from power plants, factors, and vehicles.
In early May 2017, a dust storm over Beijing sent the city’s air quality index to over 620. The US government rates readings over 200 “very unhealthy,” and 301–500 “hazardous.”
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Saharan dust creates algae blooms in the Caribbean and subtropical Atlantic. Chinese dust does the same on the west coast of America: creating toxic blooms from southern California to as far north as Alaska.
Canadian lentil fields were hard hit in 1987 by anthracnose, a fungal spotting and wilting disease. This fungal blight was brought on the wind from Asia.
