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Global warming will shift South Pacific rain band

A 2004 NASA satellite image shows a volcano erupting on Vanuatu, in the South Pacific.

Island nations can expect to see more drought and flooding

By Summit Voice

SUMMIT COUNTY — Already under the gun from rising sea levels, some South Pacific island nations could also be swamped by more extreme floods and hit by drought as global temperatures rise in response to more heat-trapping greenhouse gases in the atmosphere.

The international study, led by CSIRO oceanographer Dr. Wenju Cai, examines how the South Pacific rain band will respond to greenhouse warming.

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. Occasionally, the rain band moves northwards towards the Equator by ip to 1,000 kilometers, inducing extreme climate events.

Cai and other researchers predict the rain band will shift twice as often in the future, with a corresponding intensification of the rain band. They reported their findings in the journal Nature.

Using baseline data on atmospheric circulation and climate prediction models from the IPCC, the team found that higher concentrations of greenhouse gases will enhance enhance equatorial Pacific warming.

Although other climate cycles like El Niño are a factor, the overall warming will leads to the increased frequency of extreme excursions of the rain band.

During moderate El Niño events with warming in the equatorial eastern Pacific, the rain band moves north-eastward by 300 kilometers. 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.

In turn, countries farther northeast experience extreme floods.

“During extreme El Niño events, such as 1982-83 and 1997-98, the band moved northward by up to 1,000 kilometers. The shift brings more severe extremes, including cyclones to regions such as French Polynesia that are not accustomed to such events,”said Cai, a scientist at the Wealth from Oceans Flagship.

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.

The paper, More extreme swings of the South Pacific Convergence Zone due to greenhouse warming,was co-authored by Australian scientists Dr Simon Borlace, Mr Tim Cowan from CSIRO and Drs Scott Power and Jo Brown, two Bureau of Meteorology scientists at the Centre for Australian Weather and Climate research, who were joined by French, US, UK, and Cook Island scientists.

The research effort from Australian scientists was supported by the Australian Climate Change Science Program, the CSIRO Office of Chief Executive Science Leader programme, and the Pacific-Australia Climate Change Science and Adaptation Planning Program.

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