A 2000 year ice core record of snowfall in East Antarctica shows that reduced rainfall and drought in South West Western Australia, since the 1970s, is likely due to carbon dioxide and other greenhouse gas emissions from human activity.
The study indicates that the rainfall reduction is unlikely to be due to natural variation alone, suggesting drier conditions could become the ‘new normal’ as emissions rise.
This has implications for the management of residential water supplies and industrial and agricultural production in the South West region.
The research, led by scientists from the Institute for Marine and Antarctic Studies, Australian Antarctic Division and Australian Antarctic Program Partnership, extends previous work using a 750 year ice core record of snowfall from Law Dome, near Australia’s Casey research station.
Australian Antarctic Division glaciologist, Dr Tas van Ommen, said that between the 1970s and 2000s there was a 15-20% decline in winter rainfall in South West Western Australia and, at the same time, a 10% increase in snowfall in Law Dome.
This link between increased snowfall in Antarctica and reduced rainfall in Australia is known as a ‘teleconnection’.
“Using the 750 year ice core record we found that since the 1970s, atmospheric pressure systems south of Australia have directed more warm, moist air towards Law Dome, resulting in higher snowfall, while also bringing cool, southerly, dry winds and reduced rainfall to parts of South West Western Australia,” Dr van Ommen said.
“Our new study using an extended ice core record shows that while natural variations can produce such drought events, they are very rare.”
The team led by Yaowen Zheng, from the Institute for Marine and Antarctic Studies, used the ice core record to reconstruct rainfall in South West Western Australia for the full 2000 years.
Long climate model simulations were then used to investigate the possible roles of natural variability and external climate influences in explaining changes in rainfall.
The rainfall reconstruction showed that the drought connection observed since the 1970s is the only such event since 1250, and one of three droughts of similar duration and intensity in the full 2000 years. The other two droughts occurred in the periods around 400 and 750 CE.
“The reconstruction shows that the rainfall decrease in Western Australia is not unprecedented, but it is unusual,” Mr Zheng said.
“Our model simulations indicate that the droughts that occurred before the industrial revolution may have arisen through natural climate variability.
“However the simulations also indicate that greenhouse gases from human activity are more likely to be the dominant driver of the rainfall reduction since the early 1970s.
“Nevertheless, natural variability may also have played a role in determining both the timing and magnitude of the reduction in rainfall.”
The research is published in Climate of the Past.