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More weather extremes ahead from southern hemisphere’s largest rainband

Beef Central 06/09/2012

 

South Pacific countries and far northern regions of Australia will experience more extreme floods and droughts in response to increasing greenhouse gas emissions over the next century, according to a paper published this month in the scientific journal, Nature.

The changes will result from responses in the South Pacific Rain Band to greenhouse warming, the paper suggests.

The South Pacific Rain Band is largest and most persistent of the Southern Hemisphere spanning the Pacific from south of the Equator, south-eastward to French Polynesia. It also extends over northern regions of Queensland, the Northern Territory, and WA.

The international study, led by CSIRO oceanographer Dr Wenju Cai, focuses on how the frequency of such movement may change in the future.  The study suggested that the frequency will almost double in the next 100 years, with a corresponding intensification of the rain band.

Dr Wenju and colleagues found that increases in greenhouse gases are projected to enhance equatorial Pacific warming.  In turn, and in spite of disagreement about the future of El Niño events, this warming will lead to the increased frequency of extreme excursions of the rain band, they suggest.

During moderate El Niño events with warming in the equatorial eastern Pacific, the rain band moves north-eastward by 300km.  Countries located within the bands’ normal position such as Vanuatu, Samoa, and the southern Cook Islands experience forest fires and droughts as well as increased frequency of tropical cyclones, whereas countries to which the rain band moves experience extreme floods.

A central issue for community adaptation in Australia and across the Pacific is understanding how the warming atmosphere and oceans will influence the intensity and frequency of extreme events. The impact associated with the observed extreme excursions includes massive droughts, severe food shortage, and coral reef mortality through thermally-induced coral bleaching across the South Pacific.

“Understanding changes in the frequency of these events as the climate changes proceed is therefore of broad scientific and socio-economic interest,” Dr Wenju said.

The paper, “More extreme swings of the South Pacific Convergence Zone due to greenhouse warming,” was co-authored by Australian scientists Simon Borlace and Tim Cowan from CSIRO and Drs Scott Power and Jo Brown,  Bureau of Meteorology scientists at the Centre for Australian Weather and Climate research.

The research effort from Australian scientists was supported by the Australian Climate Change Science Program.

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