Stronger winds reduce rainfall

INCREASED carbon dioxide has replaced ozone depletion as the major explanation for reduced winter rainfall across southern Australia.

INCREASED carbon dioxide has replaced ozone depletion as the major explanation for reduced winter rainfall across southern Australia, according to a paper published today in ­Nature.

The Australian National University-led research analyses westerly winds in the Southern Ocean for the past 1000 years.

It found a rising level of carbon dioxide in the atmosphere was strengthening winds in the Southern Ocean and pushing rain that would normally have fallen in southern Australia further south towards Antarctica.

The change in weather has been particularly pronounced in Western Australia, which has lost 20 per cent of winter rains since the 1960s.

Lead researcher Nerilie Abram said the findings also explained why Antarctica was not warming as much as the Arctic.

“One of the commonly discussed reasons for westerly wind changes is ozone depletion,’’ Dr Abram said.

“But what we have shown in this study is that the increase starting in 1940 is actually far too early to be explained by ozone forcing alone.” Until this study, Antarctic climate observations were available only from the middle of last ­century.

By analysing ice cores from Antarctica, along with date 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 past 1000 years.

Dr Abram said the Southern Ocean winds were now stronger than at any other time in the past 1000 years.

“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,’’ she said.