US and Australian researchers say settlers who came to Australia 50,000
years ago and set fires that burned off natural flora and fauna may have
triggered a cataclysmic weather change that turned the country's
interior into the dry desert it is today.
Their study, which is reported in the latest issue of the journal
"Geology" supports arguments that early settlers literally changed the
landscape of the continent with fire.
"The implications are that the burning practices of early humans may
have changed the climate of the Australian continent by weakening the
penetration of monsoon moisture into the interior," Gifford Miller, of
the University of Colorado at Boulder, said.
The geological record shows that the interior of Australia was much
wetter about 125,000 years ago.
The last Ice Age changed the weather across the planet but monsoons
returned as the glaciers retreated 12,000 years ago - all except the
Australian monsoon.
The Australian monsoon now brings about one metre of rain annually to
the north coast as it moves south from Asia, but only about 33
centimetres of rain falls on the interior each year.
Mr Miller's study suggests that large fires could have altered the plant
population enough to decrease the exchange of water vapour with the
atmosphere, stopping clouds from forming.
The researchers, working with John Magee of Australian National
University in Canberra, used computerised global climate simulations to
show that if there were some forest in the middle of Australia, it would
lead to a monsoon with twice as much rain as the current pattern.
Fossil evidence shows that birds and marsupials that once lived in
Australia's interior would have browsed on trees, shrubs and grasses
rather than the desert scrub environment that is there today.
It also shows large charcoal deposits most likely caused by widespread
fires, conveniently dating to the arrival of people.
People are also blamed for killing off 85 per cent of Australia's huge
animals, including an ostrich-sized bird, 19 species of marsupials,
7.5-metre lizard and a Volkswagen-sized tortoise.
Some experts have suggested climate change caused by burning killed off
these species, rather than direct hunting by human. |
