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Changing winds send Australia’s rain to Antarctica

Winds_model

Models run at NCI have revealed why southern Australia is recording more droughts.

Using the NCI supercomputing facilities, Dr Steven Phipps from UNSW discovered that greenhouse gases have disrupted the winds that deliver rain to southern Australia, pushing them towards Antarctica instead.

“I ran a whole suite of climate model simulations to evaluate how different climate drivers might have played a role in the trends we’ve seen in the Southern Ocean winds,” he said.

“I found that prior to the 20th century, the system is dominated by natural variations. But during the 20th century, human emissions of greenhouse gases start to take over and then become the dominate driver.

“And that’s the trend that led to the southward shift in the westerly winds that’s led to the drying out of southern Australia.”

Lead researcher Dr Nerilie Abram from ANU said the findings explained the mystery of why Antarctica was not warming as much as the Arctic.

“With greenhouse warming, Antarctica is actually stealing more of Australia’s rainfall. It’s not good news: as greenhouse gases continue to rise we’ll get fewer storms chased up into Australia,” Dr Abram said.

The changing winds are trapping more cold air over Antarctica, says Dr Abram.

“This is why Antarctica has bucked the trend. Every other continent is warming.”

By analysing ice cores from Antarctica along with data from tree rings and lakes in South America, Dr Abram and her colleagues were able to extend the history of the westerly winds back over the last millennium.

 Dr Abram working on the ice core

Dr Abram working on the ice core. Photo by Paul Rogers.

“The Southern Ocean winds are now stronger than at any other time in the past 1,000 years,” she said.

“The strengthening of these winds has been particularly prominent over the past 70 years, and by combining our observations with climate models we can clearly link this to rising greenhouse gas levels.”

NCI played a fundamental role in the research, says Dr Phipps.

“NCI is the only facility in Australia that’s got the capacity for us to do something like this. We could only run the other models once, with all the climate drivers bundled in together.

“NCI made it possible to run 13 different experiments so we could break the story down and isolate a specific climate driver.

“Being able to run the model so many times means we can make some really robust conclusions.”

The study is published in Nature Climate Change.

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