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POSTED: Mon 8 February 2010

RAPID ROUNDUP: WA drought unique for 750 years (Nature Geoscience) - Experts respond

New Australian research suggests the past few decades of serious drought in the southwestern corner of Australia may be highly unusual compared with the past 750 years. The report reveals a close association between drought in southwestern Australia and high amounts of snowfall at Law Dome, East Antarctica, as a result of a pattern of atmospheric circulation that brings dry, cool air to Australia, while transporting warm, moist air to East Antarctica.

The researchers compared records of precipitation at Law Dome, Antarctica and in southwestern Australia, and found a strong inverse relationship. Ice-core data from Law Dome show that the recent snowfall anomaly at Law Dome is highly unusual relative to the variability throughout the full 750-year record, and suggests that the same may hold for the southwestern Australian drought.

The researchers point out that the airflow responsible for both southwest Australian drought and high East Antarctic snowfall is consistent with some projections for circulation changes associated with human-induced climate change.

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Dr Tas Van Ommen is a Principle Research Scientist at the Australian Antarctic Division and Antarctic Climate and Ecosystems Cooperative Research Centre, Tasmania. He is the Lead author of the research.

“This work sheds new light on the problem of understanding the drought in SW Western Australia. By identifying new processes that influence regional Australian climate, this work offers the possibility to improve understanding and reduce uncertainty in future projections of climate change. The research suggests that human influence is likely to be playing a role in the drought of recent decades and raises important questions for future trends that can only be addressed by more research.

We were surprised at first, given the complexity of climate processes, to find such a direct connection between our ice core and the climate of Western Australia. This work underscores the need for long-term records of past climate from sources like ice cores and it illustrates the important role that Antarctic climate processes play globally. Our understanding is built on observing how the climate system has changed in the past, and how it is responding now to human influence.”

Professor Neville Nicholls is Professorial Fellow in the School of Geography and Environmental Science at Monash University, Victoria.

“This is a fascinating paper, especially for those of us who have been struggling to understand the strong decline in southwest Western Australia rainfall. I'm sure we will mull over the results for quite a while. It may seem strange that scientists would use snowfall in Antarctica to estimate drought in Western Australia, but the authors' argument does hang together well, and they make a good case for concluding that the post-1970 southwest drought is very unusual. In fact their approach may even underestimate just how unusual the drought actually is. Since about 1990 snowfall at their site in Antarctica appears to have decreased but southwest rainfall has not rebounded as we might have expected from this. So the southwest drought has continued longer than we would expect from the Antarctic snow record. This indicates that some additional mechanism is affecting either snowfall or the drought. This is not surprising in a time of strong global warming. But we do need to work out these extra mechanisms.”

Professor Andy Pitman is Joint Director of the Climate Change Research Centre at the University of New South Wales.

“This is an excellent example of how long climate records from the palaeoclimate community can tell us how unusual changes seen in recent climate observations are. Their finding that the rainfall over WA is outside the range of variability over the last 750 years is a good and bad news story.

It is good for those policy makers in WA who invested in alternative sources of water based on earlier research by CSIRO and the Bureau of Meteorology. This new science suggests they made a wise decision. It is, of course, less good news for the future of water dependent industries in WA and re-enforces the urgent need for global cuts in greenhouse gas emissions.”