Increasing
aridity could lead to major problems for societies and ecosystems in
already-arid places
Warming climate may mean less rainfall
for drought-sensitive regions of the Southern Hemisphere, according to results
just published by an international research team.
Geoscientist Curt Stager of Paul Smith's
College in Paul Smiths, N.Y., and colleagues found that rainfall in South
Africa during the last 1,400 years was affected by temperature--with more rain
falling during cool periods and less during warm ones.
The findings, published in the journal
Climate of the Past, are supported by the National Science Foundation (NSF).
"The link between climate change
and rainfall in certain latitudes can have large effects on ecosystems,"
said Paul Filmer, program officer in NSF's Directorate for Geosciences.
"Plants, for example, may be able
to grow in a wider area, or conversely, be squeezed up a mountain or onto a
peninsula. When the affected ecosystem supports a food crop, that can mean a
bonanza--or a famine."
Theoretical climate models have shown
that global warming could push storm tracks southward "and away from the
mainlands of southern Africa, South America and Australia," said Stager.
"This research supports those
predictions of increasing aridity, which could lead to major problems for
societies and ecosystems in these already-arid places."
A poleward shift in winds could also
affect the flow of marine currents around the tip of Africa, changing air and
water temperatures farther afield, including in the Atlantic and Indian Oceans.
Stager, lead author of the paper,
collected sediment samples from Lake Verlorenvlei in South Africa. By analyzing
the diatoms--tiny, glassy-shelled algae--preserved in sediment cores from the
bottom of the lake, he and other researchers were able to reconstruct rainfall
patterns dating back to 600 A.D.
Two Paul Smith's College undergraduate
students, Christiaan King and Jay White, also participated in the study, along
with scientists from the University of Maine and from institutions in South
Africa and Europe.
Rainfall at the southernmost tip of
Africa is governed by a sinuous belt of eastward winds that migrate like a
meandering river, depending on the season.
In summer months, these winds drift
closer to Antarctica, carrying rain clouds over the ocean; in winter, the winds
move over the African continent.
The shifting winds bring rains that
provide much of the annual water supply.
"A poleward retreat of these winds
would have serious consequences for cities like Cape Town, for farms and
wineries, and for local animal and plant communities," Stager said.
"The same also appears to be true
for the semi-arid winter rainfall regions of South America and Australia-New
Zealand."
Michael Meadows, a scientist at the
University of Cape Town who co-authored the paper, said that hundreds of
species of rare flowering plants native to the area's fynbos ecosystem are
threatened by the changes.
"These plants are tough, and are
already used to dry conditions," Meadows said. "But more aridity
could make fires more frequent, which could damage the soils and make it even
harder for the plants to survive.
"Unfortunately, this is their only
native habitat, so such a change might threaten their existence."
According to Stager, such links to
mobile storm tracks make these regions exceptionally vulnerable to the effects
of greenhouse gas build-up.
"When it comes to climate change,
there's more to consider than warming alone," he said. "In places
like these, increasing drought could bring far-reaching challenges."
-NSF-
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