Earth is a system
of systems. That means that even small changes
in one part of the planet can have effects felt all the way around the globe.
The world’s largest,
hottest desert --the Sahara -- is nearly the size of the continental United States.
Each year millions of tons of its nutrient-laden
dust are swirled up into the atmosphere by easterly trade winds,
and carried across the Atlantic. The plumes can make
their way from the African continent as far as the Amazon rainforest,
where they fertilize the plant life of one of Earth’s most biodiverse regions.
The dust carries phosphorus, a nutrient necessary
for plant growth. As it travels around
the globe, the resultant layer of dust can easily be seen from space.
This was especially true over the month of June 2020,
when satellites and astronauts observed an unusually large quantity
of dust, nicknamed the Godzilla plume, heading west from Northern Africa.
It thinned out over its 3000-mile
mile journey, depositing nutrients into the ocean and land below.
To travel such a distance requires strong winds.
These winds are from the trade wind system. The trade winds are affected
by differences in sea surface temperature between the northern and southern Atlantic Ocean.
Over the last century, the North Atlantic
Ocean has experienced a shift in sea surface temperature every few decades,
referred to as the Atlantic Multidecadal Oscillation,
or the Atlantic Multidecadal Variability.
Warmer sea surface temperatures in the north, like those observed in recent years,
lower the contrast between north and south and change wind circulation,
slowing the trade winds down.
The northern and southern trade winds converge along a latitudinal band called the
the Intertropical Convergence Zone, or ITCZ, which is where
rainfall is most concentrated in the region. The ITCZ
and its connection to sea surface temperature and
wind has been supported by observations over thousands of years.
Though the band of rain always moves north and south
with the seasons, a recent NASA study shows that the ITCZ
has been migrating farther and farther north over the last several decades,
likely a result of the warming climate. As the band covers more of the Sahara,
increased quantities of rainfall over the desert dampen down
the dust, making it less likely to be carried off by the already
weakened winds. As the climate changes,
dust activity will continue to be affected. NASA researchers
predict that within the next century we will see dust transport
approach a 20,000-year minimum.
NASA