{News} 081117! Coral study points to more harsh droughts
Coral study points to more harsh droughts
BY NYSSA SKILTON
17/11/2008 8:52:00 AM, The Canberra Times
New coral records have revealed Australia is likely to experience more frequent and intense droughts.
Scientists studying the tropical weather patterns stored in corals have discovered climate variability in the Indian Ocean has intensified during the 20th century. This suggests Australia and the region can expect less rain while eastern Africa gets wetter.
An international research team, led by the Australian National University, analysed corals from tropical waters north-east of Australia to build a picture of climate change going back to 1846.
Their findings are published in the journal Nature Geoscience, available online today.
To date, reliable records of the Indian Ocean Dipole a climate phenomenon similar to El Nino go back about 50 years.
Palaeoclimatologist Mike Gagan, of the ANU's Research School of Earth Sciences, said the researchers' techniques allowed them to analyse sea-surface temperature and salinity stretching back hundreds, even thousands, of years.
Indian Ocean Dipole events occur when the ocean temperature and winds along the equatorial Indian Ocean reverse from their normal state. These changes bring drought to western Indonesia and southern Australia and heavy rains to eastern Africa and southern India.
Dr Gagan said the frequency of dipole events was increasing. ''In the last 160 years, there's been about 21 dipole events that we can see, and there's only been about five very strong events,'' he said.
''But it turns out, four out of the five very strong events have occurred since 1960, and three of the very strong events have occurred since 1994.''
Dr Gagan said this meant farmers across southern Australia would not be able to rely on spring rains as they might have in the past.
''We have one dipole event every four years now on average. Who knows, there may be one every two years in 30 or 40 years,'' he said.
The researchers analysed giant porite corals, some aged 400 years, to glean information about past conditions. They drilled cores from the centre of the coral and studied the chemistry preserved in the skeleton of the coral.
''In trees, you get annual growth bands. In coral, you get annual changes in coral density, and you can count these annual density bands to keep track of the time,'' Dr Gagan said. ''We analyse it virtually month by month.''
He said the Indian Ocean Dipole was like ''the canary in the mine of climate change''.
But there was hope. ''If we can even level off CO2 and get it to be stable, even if it's a higher level, we might not like the climate that we have, but at least it's going to be more predictable and easier to adapt to,'' Dr Gagan said.
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