Climate change could amplify drought in east Indian Ocean
Pastor Dale Morgan
Climate change could amplify drought in east Indian Ocean*
PARIS, Jan 17 (AFP) Jan 17, 2007
Climate change could worsen the impact of an El Nino-like weather system
in the Indian Ocean, bring brutal droughts to parts of Indonesia and
Australasia, a study published on Thursday says.
The weather system is called the Indian Ocean Dipole (IOD), a
recently-discovered phenomenon that strikes the tropical Indian Ocean at
various intervals, usually several years apart.
Under it, the surface temperature of the sea drops sharply in the
southeastern part of the Indian Ocean, off Indonesia and the northern
coast of Australia.
At the same time, the temperature rises in the western part of the
Ocean, off the eastern coast of tropical Africa.
The result is very disruptive, bringing droughts to Indonesia and parts
of Australia, and heavy rain to semi-arid parts of Africa.
Unlike the Pacific's El Nino effect, which can last a couple of years,
the IOD usually eases within months as temperatures even out on both
sides of the ocean.
As the IOD was only discovered in 1999, very little is known about how
it works, especially the climate mechanisms that cause it to be unleashed.
Researchers in Britain, led by Nerilie Abram of the British Antarctic
Survey (BAS) in Cambridge, used records from ancient Indian Ocean coral,
whose growth is affected by sea temperatures and rainfall, as an
indicator for IOD events stretching back into the distant past.
Looking at such records going back 6,500 years, they found that the big
driver for the IOD is the monsoon. Years with severe monsoons triggered
an IOD.
The finding is worrying, they say.
Monsoons are also linked to the El Nino. When an El Nino happens,
monsoons tend to be weaker -- which thus diminishes the risk of an IOD
event.
But man-made global warming is breaking down this link, and the trends
are towards stronger monsoons, said Abram.
That, as a result, suggest Dipole events will become more frequent, she
said in an interview.
"The monsoon is affected by El Nino but with global warming, that
relationship is breaking down and the monsoon is strengthening
independently of El Nino," said Abram.
"In Indonesia, droughts are likely to be shifted to the time of year
when they normally expect the most rainfall, so the impact of that could
be quite severe for the people who are trying to live in that area," she
said.
"At the moment, Indian Ocean Dipole events already have a dramatic
effect on the climate in this area. They already have droughts and
wildfires in Indonesia that are a threat to human health and the
environment."
The last Dipole event occurred last year, and its predecessor was in the
last 1990s.
"Normally the Dipole events peak in October and November, then after the
monsoon winds change direction, then it dissipates and things start to
go back to normal again," she explained.
The paper appears in the weekly British science journal, Nature.