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Saturday, February 21, 2015

Climate change is expanding the tropics

Waves crash into a breakwall after Tropical Cyclone Marcia made landfall near Yeppoon

As the air and the seas heat up, the band in which tropical cyclones form is creeping towards the poles:

Climate change is resulting in the expansion of the tropics at the rate of 150-300 kilometres every 30 years, bringing more regions in the path of potential cyclones, Professor Turton said. (See his essay in the 2014 State of the Tropics report.)

"The research is suggesting that, in a warmer world, we'll get more intense cyclones because there'll be more energy in the oceans and also the atmosphere," he said.

Climatologists say the atmosphere can hold about 7 per cent more moisture for every degree of warming, potentially adding clout to major storm events.

Last year, a study led by scientists at the US based National Oceanic and Atmospheric Administration, The Poleward Migration of the Location of Tropical Cyclone Maximum Intensity, argued that the areas where cyclones were reaching their most powerful were shifting towards the North and South Poles at the rate of 56 kilometres a decade.

"With their devastating winds and flooding, tropical cyclones can especially endanger coastal cities not adequately prepared for them," the NOAA said.

"Additionally, regions in the tropics that depend on cyclones' rainfall to help replenish water resources may be at risk for lower water availability as the storms migrate away from them."

Professor David Karoly, a scientist at the University of Melbourne, said the prospect of fewer - but more intense - cyclones in the western Pacific basin under global warming is because of expected changes to atmospheric circulation.

The expansion of the tropics would likely result in a strengthening of the high-pressure belt over southern Australia, leading to reductions in rainfall, Professor Karoly said.

Some of that shift is already evident in south-western WA, where cool season rainfall in particular has dropped sharply in recent decades, according to the CSIRO and the Bureau of Meteorology. Similar reductions in rainfall are also becoming evident across the south-east.

Read more here.

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