vital role in climate change over the last 23,000 years.
In the words of US oceanographers and Earth scientists, “North Africa
exports teragrams of wind-blown mineral aerosol over the tropical North
Atlantic each year, with significant climate and biogeochemical
A teragram is a million tonnes, and the quantities airlifted into the
sky from the Sahara and the Sahel each year by the trade winds and
blown abroad would be enough to fill 10 million heavy trucks.
About 11,000 years ago, the continent’s total exports of fine dust began to fall dramatically, the researchers report in Science Advances journal.
The lower levels of fine particles in the sky may have allowed more
sunlight to hit the ocean waters, may have warmed surface temperatures
by 0.15°C, and may have helped whip up monsoons over North Africa to
make the conditions far more temperate than they are today.
“In the tropical ocean, fractions of a degree can cause big
differences in precipitation patterns and winds,” says one of the
report’s authors, David McGee, assistant professor of paleoclimate and
geochronology at the Massachusetts Institute of Technology.
“It does seem like dust variations may have large enough effects that
it’s important to know how big those impacts are on past and future
Researchers have already established the importance of windblown dust, both as a source of mineral nutrient for marine life and for the rainforests of Brazil. Scientists have even identified dust kicked into the air by heavy rain.
But the latest study focused on the changing pattern of dust delivery
from the peak of the last Ice Age to the present, the role it may have
played in bygone climate change, and its importance in the human story.
North Africa was once a more temperate and hospitable place. Dr McGee
says: “There was also extensive human settlement throughout the Sahara,
with lifestyles that would never be possible today.
“Researchers at archaeological sites have found fish hooks and spears
in the middle of the Sahara, in places that would be completely
uninhabitable today. So there was clearly much more water and
precipitation over the Sahara.”
Some of this may be explained by subtle cyclic shifts in the
planetary axis, exposing the northern hemisphere to more sunlight, more
evaporation and more rainfall over land. Read More