WA weather records play big role in climate jigsaw puzzle

[Published in the West Australian, 8/2/2010] One hundred years ago Douglas Mawson was preparing for his historic voyage to Antarctica. Mawson’s purpose was to be among the first to explore the frozen continent and to research a part of the globe that was devoid of scientific observation. From these pioneering efforts two great Australian legacies evolved: Australia’s claim to 42 per cent of the Antarctic continent and a long and proud reputation for world class and groundbreaking Antarctic science. This week, in the journal Nature Geoscience, Australian glaciologists Tas van Ommen and Vin Morgan describe how rainfall in one of Australia’s most important agricultural areas is linked to weather atterns and snowfall in Antarctica. Using an ice core drilled at Law Dome near Casey Station in the Australian Antarctic Territory, Dr van Ommen and Mr Morgan have shown that higher snowfall in that part of Antarctica coincides with drought in South-West WA. The decline in rainfall of about 17 per cent in this part of WA since the 1960s corresponds to an increase in snowfall at Law Dome. This discovery could become an important piece of Australia’s weather and climate jigsaw puzzle. While there are complex weather and climate factors that may explain this important finding, the significance of this serendipitous discovery is worth exploring. The scientists who drilled the ice cores were not doing research on rainfall. Rather they were attempting to discover and describe in fine detail the recent (up to 10,000 years ago) climate of Antarctica. They were able to do this because of a history of research dating back to the late 1950s and subsequent studies of glaciers and ice cores by Australian scientists over a long period. Australia’s current Antarctic science efforts began in 1954 with the establishment of Mawson station, the oldest Antarctic continental research station. Our ability to make groundbreaking discoveries in Antarctica relies on a history of effort and achievement, and the ability to plan and support future scientific endeavour. Australia is well placed to play a central role in research on global climate and climate change through its efforts in Antarctica. In order to do this it is crucial that Australia continues to adequately fund and support its Antarctic efforts -- a point made strongly by the Australian Strategic Policy Institute in its report Frozen Assets: Securing Australia’s Antarctic future. There is much, much more to be discovered and learnt by those following in Mawson’s footsteps. ----------- 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." ----------- Media Brief: Antarctic ice provides clues to long-term drought in southern Australia In a study published Sunday 7th February 2010 in the international journal Nature Geoscience Australian researchers detail a link between Antarctic snowfall and drought in southwest Western Australia. The study uses an ice core to reconstruct annual snowfall over the last 750 years at Law Dome, on the Antarctic coast to the far south of Western Australia. The results reveal unusually high snowfall over the last few decades that is linked with severe drought in Western Australia over the same period. The southwest corner of Western Australia has seen a sharp decline in winter rainfall since the late 1960s that has had a profound impact on the area. This is believed to be due to a range of factors which include a general southward shift in storm tracks that bring rain in prevailing westerly winds. However, this shift has been weak in winter, and a full explanation for the drought remains somewhat of a puzzle. Also, weather records from the region extend only back to around the start of the 20th Century, making it difficult to assess how unusual the drought in recent decades has really been. The 750-year ice core record provides a longer period for assessment, and because of the highly detailed and well-dated Law Dome core, it also provides the ability to compare recent decades with detailed meteorological data. This comparison shows that for high snowfall years there is a distinct pattern of large scale atmospheric circulation over the Southern Ocean between Australia and Antarctica. This circulation carries warm, moist air southward to East Antarctica and Law Dome, and at the same time carries cold, dry air from the south onto Western Australia’s southwest corner. This is the first time this pattern of circulation, which drives large-scale northward and southward flows of air, has been associated with drought at mid-latitudes and this study shows that it is likely to be a major contributor to the drought. The long-term ice core data reveal that high snowfall at Law Dome in recent decades is unprecedented in the last 750 years and lies well outside the natural range of variability. This indicates that the drought in southwest Western Australia may be similarly unusual. The signature northward and southward flow that links Law Dome and Western Australia also appears in some climate model runs with greenhouse gas and ozone driven climate change. These results suggest that the drought is at least partly the result of human induced climate change.

Authorised by the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre October 2019.

The ACE CRC was established and supported under the Australian Government’s Cooperative Research Centres Program.

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