Australasian Science: Australia's authority on science since 1938

The East’s Big Dry

By Stephen Luntz

Rainfall in eastern Australia over the past 90 years is less than for the previous seven centuries, Australian Antarctic Division scientists have concluded following the discovery of an unexpected rainfall proxy.

Australia lacks finely scaled climate proxies, so little is known about rainfall patterns prior to the late 18th century. However, Dr Tessa Vance found that salt levels in ice laid down during summer at Law Dome, Antarctica, indicate the presence or absence of El Niño conditions, which are a major factor in eastern Australian droughts.

“The El Niño-Southern Oscillation, or ENSO, climate mode predominantly drives rainfall in eastern Australia and is one of the factors that affects winds in the Southern Ocean,” says Vance, who revealed in the Journal of Climate that El Niño events weaken the winds that at other times dump salt inland at Law Dome.

“Every ENSO is different,” says Vance. “The 1998 event was very strong globally but had little effect on Australian rainfall, while the weaker 2002–03 event produced a record-breaking drought. However, when you have a period of stronger El Niños over time there will be drier conditions.”

Vance studied the same ice core her colleague Dr Tas van Ommen had previously used to demonstrate an inverse relationship between precipitation at Law Dome and precipitation in the south-west of Western Australia (AS, April 2010, p.9). The core revealed a period of El Niño conditions from 1000–1260, but higher salt deposition until 1920.

Vance now plans to extend the record a further 1000 years, but doubts that compression and spreading of the ice will allow her to observe the fine-grained detail required any further back.

“We can’t tell from this proxy alone whether Australia was warmer from 1000–1260 or just drier. El Niños tend to give a warm year globally, and there is some evidence warmer temperatures force stronger El Niños,” Vance says. However, she doesn’t consider the relationship reliable, unlike with drought.