Ancient Burning Tied to Australia Desert
12/12/97
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Headline: Ancient Burning Tied to Australia Desert
Source: United Press International
Date: 12/12/97
Byline: Lidia Wasowicz, UPI Science Writer
Copyright 1997 by United Press International
SAN FRANCISCO, Dec. 12 (UPI) -- It seems even our earliest ancestors
had a tendency to fool with Mother Nature, possibly altering climate and
triggering ecological upheavals.
New research indicates while not burning fossil fuels as their
modern-day descendants are wont to do, the first human inhabitants of
Australia systematically burned vegetation, with similar consequences.
The possibility that aborigines' land-use practices some 50,000 years
ago shifted climate patterns down under and triggered the transformation
of a once lush region into a vast wasteland was presented at the
American Geophysical Union Fall Meeting in San Francisco.
Gifford Miller of the Institute of Arctic and Alpine Research at the
Universtiy of Colorado, Boulder, says, ``The systematic burning of
vegetation by aboriginals, beginning some 50,000 years ago, may have
changed the climate and kindled the desertification of Australia's
interior.''
Climate records sealed in lake sediments indicate annual summer
monsoons routinely drenched northern Australia from some 150,000 to 40,
000 years ago -- until man came on the scene.
Says Miller, ``Although the intensification of African and Indian
monsoons at the beginning of the Holocene Period some 10,000 years ago
suggests such storms were increasing on a global scale, the Australian
monsoons inexplicably failed to follow suit, according to paleoclimate
evidence.''
Monsoons, scientists know, are driven by glacial activity and
periodic changes in solar radiation.
As Miller puts it, ``Since Earth was experiencing marked increases in
monsoonal activity in the early Holocene, something regional must have
modulated the Australian monsoon.''
The only mechanism with enough force to alter this natural picture,
he says, is vegetation. The role of vegetation can be clearly seen in
the Amazon rain forest. There, half the rain that falls is recycled
during the wet season through plant transpiration and evaporation.
According to archeological records, humans arrived in Australia from
southeast Asia some 50,000 years ago, just about the time the climate
started to change.
Says Miller, ``Consistent burning by these people during dry periods
may have altered the basic ecosystem, preventing the normal recovery of
vegetation during the subsequent wet phase.''
As a result, he speculates, Australia's interior today gets less than
12 inches of rain a year -- in marked contrast to the 80 inches that soak
the city of Darwin on the continent's northern coast during the monsoon.
A computer model developed by Miller and his colleagues from INSTAAR,
the National Center for Atmospheric Research in Boulder and Australian
National University indicates adding vegetation to the barren landscape
would more than double the current amount of monthly rain during
monsoons.
Says Miller, ``This suggests during peak periods of the Australian
monsoons the penetration of moisture is highly sensitive to vegetation
type and the failure of the early Holocene summer monsoon may be a
direct consequence of human activity.''
Further evidence supporting this theory comes from studies of fossil
eggshells from such flightless birds as ostriches and emus that call
Australia home. Marilyn Fogel of the Carnegie Institution in Washington
and Beverly Johnson of INSTAAR have been analyzing the carbon inside the
fossil eggshells collected from an arid region in south Australia to
determine the birds' diet.
Emerging from this study is a picture of dramatic change. The lush
grasses that dominated the area from about 70,000 to 45,000 years ago
during the monsoons gave way to a more arid, mixed vegetation by 35,000
years ago -- in conjunction with the waning of the monsoon.
The changing vegetation, the researchers theorize, helped establish
present rainfall patterns.