2013
sandstorm, Beijing. (Feng Li/Staff/Getty Image News) |
Due to
what was widely reported as a massive sandstorm, Beijing's skies turned orange
recently.
The issue,
at least in terms of public health, is that there was no sandstorm. There had
been a dust storm.
This may
appear to be an exercise in geological minutiae, but it represents a
significant distinction, and it boils down to a matter of scale. Sand grains
are mineral particles with a diameter greater than 0.06 mm, the kind that
scratch your ankles on a windy day at the beach and ruin your picnic by making
your sandwiches crunchy.
Beijing and other parts of northern China hit by biggest sandstorm in 10 years; at least 6 dead, 81 missing in neighboring Mongolia pic.twitter.com/rlJa0stgRf
— BNO News (@BNONews) March 15, 2021
Dust is a
much more serious problem than blowing sand.
Dust
particles (also known as silt and clay by some geologists) are smaller grains
that feel silky to the touch and do not scratch the skin. Importantly, these
smaller, lighter grains have the potential to travel much further.
They are
not dependent on the sand grains' short-distance ballistic hops, but may become
suspended in a global atmospheric process that transports them around the
globe. Dust, not sand, can easily travel hundreds of kilometers or even around
the world.
The grain
size is also important because finer dust particles – those less than 10
micrometers (pm10) and particularly less than 2.5 micrometers (pm2.5) – can be
drawn deep into the lungs, posing serious health risks.
Dust
storms have existed in China for a long time, long before humans had a
significant impact on the landscape. Huge amounts of dust were produced by the
advance and retreat of ice sheets during the past 2.6 million years, eventually
settling to form loess deposits.
The
Chinese Loess Plateau, which covers an area greater than France, has accumulated
to a thickness of up to 350 meters over millennia. The loess is nutrient-dense
and makes for a productive agricultural soil. It is primarily this farmland
that is being eroded and recirculated as dust by the wind.
March 2021
dust storm, showing winds blowing from the Loess Plateau towards Beijing.
(NASA) |
Is the
frequency of dust storms changing now, after such drastic changes in the past?
Extrapolating from a single country, such as China, to the rest of the world is
not a good idea because the pattern is intricate and there is a lot of
variability even within the region.
There is
evidence that the frequency of dust storms has decreased in China over the last
few decades. Other studies have suggested that dust storms have become more
common in some parts of China over the centuries.
The
picture is similarly complicated on a global scale. Dust storms have increased
in frequency in Israel over the last 30 years, according to studies, while they
have decreased in frequency in other areas, according to other research.
Part humans,
part nature
So, what
is the source of the current dust storms? Is this a purely natural process, a
result of climate change, or a result of land mismanagement? The answer is
complicated, and it most likely contains some of each of these factors.
A recent
study looked at the impact of various dynastic regimes and climate change on
the frequency of dust storms in China over the last 2,000 years, and found that
an increase in dust storms correlated with both population growth and stronger
Asian monsoon circulation.
Surprisingly,
increased dust storm activity occurred during periods of increased rainfall,
which allowed dynasties to prosper and populations to expand, resulting in
increased demand for agricultural land clearance.
The
process is mostly natural in other places. Despite its small size, the remote
and sparsely populated Bodélé Depression in Chad, in the Sahara, is the world's
largest source of atmospheric dust.
This is
due to a combination of hyper-arid desert conditions, a highly erodible surface
made up of fine relic lake deposits, and nearby mountains that funnel wind
across the surface.
On the
surface, the story of dust storms appears to be a relentlessly grim picture of
landscape erosion, loss of productive agricultural land, atmospheric pollution,
and health consequences, but there is a final aspect to the story.
Dust
storms are sometimes referred to as "fertilizers" of the oceans'
phytoplankton, which is the foundation of most ocean food chains, because of
their role in transporting essential mineral nutrients, most especially iron,
to the oceans.
According
to a 2014 study, wind-blown Saharan dust is responsible for more than
three-quarters of dissolved iron in the northern Atlantic, and other studies
have indicated that Saharan dust is important in fertilizing the Amazon
rainforest with the nutrient phosphorus.
As a
result, the story of windblown desert dust, such as that seen over Beijing this
week, is complex and global.
Originally Published By The Conversation. Read the Original Article Here.
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