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Dust blown all the way out of the Sahara Desert hits Texas this week, which happens around this time every year.
About 6,000 years ago, North Africa was covered by huge lakes that were home to microscopic creatures. The dust that now blows over from Africa and visits us every summer consists of the remains of these ancient lake dwellers. It’s amazing.
But it is a more immediate concern for asthmatics and those with respiratory illnesses. The Texas Commission on Environmental Quality says dust is partly responsible for moderate air quality in many parts of the state, including Austin, this week.
If you are sensitive to particulate pollution, the environmental protection agency recommends that you reduce your outdoor activities. On the other hand, the annual clouds of dust can make for some lovely sunsets and help fertilize the Amazon rainforest.
Read more about these clouds of dust below.
The following was originally released in 2018:
They contain the remains of ancient life
About 6,000 years ago, North Africa was a wetter place. Lakes covered much of what is now the Sahara and housed microscopic creatures called “diatoms”. When the lakes dried up, the remains of these creatures remained.
Credit University of Nottingham / University of Nottingham
Saharan dust under an electron microscope.
The diatoms became “this whitish, powdery, chalky stuff,” says Charlie Zender, who studies atmospheric physics at the University of California at Irvine.
Zender says that “chalky stuff” is rich in minerals and so small that it can move really well in the wind. A lot of wind blows in the Sahara, so every summer storms push thousands of tons of dust into the atmosphere.
You can prevent hurricanes from forming
Once in the air, the long-dead diatoms and everything else begin to fly west towards America on a wind pattern known as a “tropical wave”.
“You can think of it as a layer of cake between about 1 and 3 miles above the ground [earth’s] Surface. So it’s in a 2 mile layer as it travels across the ocean, ”says Jason Dunion, a research meteorologist with the National Oceanic and Atmospheric Association.
On the way, says Zender, the dust cloud drips minerals onto the earth, which fertilize the ocean. It also prevents hurricanes from forming, Dunion says.
“The dry air, the very strong winds, and the warming we get from these dust outbreaks … all act to quell hurricane activity,” he says.
They also prevent storms from forming on land. Since storms are the main thing that cools Texas in summer, the presence of the dust adds to the intense heat.
They reflect sunlight and cool the earth
The dust clouds increase heat on land by absorbing sunlight and deter storms, but over the ocean, Zender says, they cool the atmosphere by reflecting sunlight back into space.
“On the net, this dust helps cool the planet a little, just a little, but any bit of cooling we can get to offset global warming gases is helpful,” he says.
While some researchers speculate that global warming could increase the intensity of African dust clouds in some parts of the world, Dunion says it is still unclear how the phenomenon will play out.
Climate change could actually reduce the dust clouds, he says, by reducing the occurrence of the “tropical waves” that they move on.
They make sunsets more beautiful, but they cause asthma
National Oceanic and Atmospheric Administration
A layer of Saharan dust in the sky.
The shape of the dust particles has at least one advantage: they can make the sky look beautiful.
“Because of their shape, they tend to scatter the sunlight more in the morning and in the afternoon,” says Dunion. “It is really this sunrise / sunset time that you can really appreciate over your head.”
But there is also one major drawback: these fine particles can get into the lungs and worsen symptoms in asthma sufferers.
They fertilize the earth
Perhaps the most important role is played by dust when it is not traveling to Texas, but when it is visiting South America in winter. Then the nutrient-rich remains of these long-dead microorganisms fertilize the Amazon rainforest, says Zender.
“The great mother Africa still feeds her former child South America with nutrients from the African desert,” he says.
That will soon happen as our days get shorter and the sun moves the waves of the dusty wind away from us south.
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