Climate: Study links deadly 2010-2011 Australia floods with long-term ocean warming

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A NASA Earth Observatory satellite image shows swollen rivers in northwestern Australia during record-setting floods in 2010-2011. Visit this NASA page for more info.

‘Take action to forestall global warming …’

Staff Report

Deadly floods that swept across Australia in 2010 and 2011 were at least partly fueled by long-term warming in the Indian and Pacific oceans, according to a new study that highlights some of threats posed by human-caused climate change.

The research, published in Geophysical Research Letters, shows that ocean warming can have profound effects on atmospheric circulation, delivering huge amounts of moisture to land areas under certain conditions.The floods in Australia’s northeast state of Queensland claimed 35 lives, caused $2.38 billion damage, flooded 28,000 homes and left 100,000 people without power. So much rain fell on Australia that it led to a rare filling of Lake Eyre, a large lake system in the interior of the country, and caused a drop in global sea level.

“The sea surface temperatures around Australia during 2010/2011 were on average 0.5°C warmer than they were 60 years ago,” said lead author Caroline Ummenhofer, a physical oceanographer with Woods Hole Oceanographic Institution. “While many past studies have found a global warming link to heat extremes, this study is one of the first to show how ocean warming can impact a heavy rainfall event.”

Both a strong La Niña event and long-term ocean warming contributed to the unusually warm ocean conditions around Australia during 2010 and 2011. During that summer, the sea surface temperatures were particularly warm in the eastern Indian Ocean, western Pacific warm pool region – to the north and east of Papua New Guinea – and the Coral Sea.

Ummenhofer and her colleagues developed models to understand how different factors contributed to the unusual conditions. One experiment included the long-term warming in addition to the La Niña sea surface temperatures, while the other had removed the warming trend. Their research determined that due to warmer sea surface temperatures, Australia was three times as likely to get this much rain during a strong La Niña event.

In fact, rainfall in northeastern Australia ended up 84 percent above average and soil moisture measurements were the highest recorded since 1950.

“The additional warming of the oceans has profound impacts on the atmosphere. It increases the amount of moisture in the atmosphere and can intensify rain-producing circulation conditions,” said co-author Prof Matthew England from the ARC Centre of Excellence for Climate System Science.

“This is why in 2010/11 more moisture was brought onshore along Australia’s east coast. Stronger rising motion over the northeast resulted in higher rainfall, making it more likely for Australia to suffer extreme rainfall conditions during this strong La Niña.”

In addition to the warming oceans bringing more rainfall, previous research has also shown that as a result of global warming, strong La Niña and El Niño events are likely to become more frequent.

“Australia has long been acknowledged as a country of extremes but this research suggests extreme rainfall events may become far more frequent in a warming world,” said Ummenhofer. “As we come into climate change talks in Paris, this research offers yet another incentive for countries around the world to take action to forestall global warming.”

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