Climate Change Perturbs Asian Monsoon Pattern

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Climate Risk Analysis company and coworkers detected a trend toward more intense east-west contrasts in the surface temperature of the Indian Ocean region over past 150 years. As the contrast influences the monsoon rainfall pattern, the trend may impose a long-term socioeconomic threat.

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But uncertainty does not warrant inaction. Implementing a long-term monsoon risk management may be less costly.

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Analysis of past Indian Ocean temperatures reveals systematic increases of intense east-west contrasts related to climate change. This can influence monsoon rainfall patterns in coming decades.

Climate Risk Analysis, a company in Hanover, Germany quantified the trend on data measured by colleagues in the United Kingdom, Australia, Indonesia, and the United States. The study, to appear in the journal Nature Geoscience (December issue), is led by Nerilie Abram from the British Antarctic Survey in Cambridge and Michael Gagan from the Australian National University in Canberra.

Climate changes over decades to centuries are important to quantify. Their systematic nature is a signal standing out against daily weather noise. This information is useful for prediction.

For deciphering changes of Indian Ocean temperature, Abram and colleagues consulted corals. The coral carbonate skeleton reports via its oxygen isotopes the water temperatures when the coral grew. The scientists found an old coral colony on Mentawai Island, about 200 km offshore of Sumatra. In the mass-spectrometer, the coral disclosed its secret and provided a temperature record that goes back to 1858. No direct measurements from that crucial, eastern part of the Indian Ocean go back that far. Combining the Mentawai data with existing data from the western part yielded a series of east-west temperature contrast. Climatologists denote that contrast as Indian Ocean Dipole (IOD).

Manfred Mudelsee from Climate Risk Analysis found that a hundred years ago only every eighteen years an intense IOD occurred while at present it is every three to four years. Temperature differences generate winds, and the IOD influences the Asian monsoon system. Ongoing climate changes in the region may therefore also change rainfall patterns, with socioeconomic consequences.

"Risk estimations have inherent uncertainties, coming ultimately from our incomplete knowledge about the climate", says Mudelsee. "But uncertainty does not warrant inaction. Implementing a long-term monsoon risk management may be less costly."

About Climate Risk Analysis:
Climate Risk Analysis is a research company working on risk quantification of extreme weather or climate events. Other recent publications deal with Canadian wildfires or hurricanes in the Boston area.

Abram, Gagan, Cole, Hantoro, Mudelsee (2008) Recent intensification of tropical climate variability in the Indian Ocean. Nature Geoscience. (doi:10.1038/ngeo357)

Besonen, Bradley, Mudelsee, Abbott, Francus (2008) A 1000-year, annually-resolved record of hurricane activity from Boston, Massachusetts. Geophysical Research Letters 35:L14705. (doi:10.1029/2008GL033950)

Girardin, Mudelsee (2008) Past and future changes in Canadian boreal wildfire activity. Ecological Applications 18:391. (doi:10.1890/07-0747.1)

Dr. Manfred Mudelsee, CEO
Climate Risk Analysis
+49 511-91701390
mudelsee at mudelsee dot com


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