19 November 2008

Coral forecast for climate: drier for Australia and Indonesia

A study of long-lived corals reveals Australia and Indonesia are likely to experience more frequent and intensified droughts, while eastern Africa is likely to get wetter. Drier weather is likely in western Indonesia and southern Australia and heavy rains to eastern Africa and southern India, leading to severe impacts on societies and ecosystems.

Corals reveal Australia's parched future
Australian National University
Science Alert 17 Nov 08;
New coral records have revealed that Australia and Indonesia are likely to experience more frequent and intensified droughts, while eastern Africa is likely to get wetter.

Scientists studying the history of tropical weather patterns stored in long-lived corals have discovered that climate variability in the Indian Ocean has intensified during the 20th century, with implications for drought in Australia and the region. The findings are published in the journal Nature Geoscience.

The ANU-led international research team analysed corals from tropical waters northeast of Australia to build a continuous picture of climate change going back to 1846. They’ve found a recent increase in the frequency and severity of the Indian Ocean Dipole – a climate engine that has a dramatic effect on rainfall in the countries surrounding the Indian Ocean.

“To date, we’ve only had reliable instrumental records of the Indian Ocean Dipole (IOD) going back 50 years,” explains Dr Mike Gagan from the Research School of Earth Sciences at ANU. “But our technique of using oxygen isotopes from coral skeletons allows us to analyse sea-surface temperature and salinity for hundreds, sometimes thousands, of years.

“We’ve found that the IOD has lately been occurring every four years, as opposed to every 20 years around the turn of the century. We’re seeing a clear trend towards these events becoming stronger and more frequent.”

The researchers say that IOD events occur when the ocean temperature gradient and winds along the equatorial Indian Ocean reverse from their normal state – in a way, it is the Indian Ocean’s equivalent of the El Niño Southern Oscillation. These changes bring drought to western Indonesia and southern Australia and heavy rains to eastern Africa and southern India, leading to severe impacts on societies and ecosystems.

“All sorts of modelling suggests that greenhouse warming will lead to strengthened Asian monsoon rainfall and more persistent El Niño-like conditions during the 21st century,” Dr Nerilie Abram says. “Our research now indicates that this is also likely to be accompanied by an increase in IOD events. This means the picture is grim for southern Australia in particular, but it also shows just how important learning more about the link between the Indian Ocean and global climate will be for our future.”

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