Volcanic blasts can boost SE Asia rains -study

SINGAPORE Fri Nov 5, 2010 1:41am EDT

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SINGAPORE (Reuters) - Scientists studying tree rings to reconstruct the past have found that major volcanic eruptions can boost rains in Southeast Asia, challenging a common perception of volcanoes as purely destructive forces.

Studies in the past have shown massive eruptions such as the 1815 Tambora blast, and Krakatau in 1883, both in Indonesia, dimmed temperatures globally and wiped out crops.

Researchers at Columbia University's Lamont-Doherty Earth Observatory in the United States wanted to study the impacts on the Asian monsoon, whose rains are vital to crops and livelihoods for billions of people.

The only way to figure this out was to go back in time. They studied the growth rings from centuries-old trees from about 300 sites across Asia, in a study published in the online edition of the journal Geophysical Research Letters.

They studied the impacts on rainfall from 54 major eruptions going back 800 years by measuring how this affected trees' growth. Narrow, thin growth rings show low rainfall and the opposite for good rains.

The tree rings showed that huge areas of southern China, Mongolia and surrounding region consistently dried up in the year or two following big volcanic blasts, while mainland Southeast Asia received more rain.

Explosive eruptions send up sulphur compounds that turn into tiny sulphate particles high in the atmosphere, deflecting some of the sun's energy. The cooling of temperatures at ground level can last for months or years.

The release of the research comes during a series of violent eruptions of Indonesia's Mount Merapi on Java island, with the mountain erupting again on Friday and the death toll reaching almost 100.

These eruptions, though large, do not yet appear to have the potential to affect global temperatures, a press release accompanying the study said.

LINK TO EL NINO?

The authors, led by Kevin Anchukaitis of the observatory, say their study underscores the close interaction of the atmosphere and oceans and also challenges existing climate models.

"Most climate models incorporating known forces such as changes in the sun and atmosphere have predicted that volcanic explosions would disrupt the monsoon by bringing less rain to Southeast Asia," a statement said.

The findings, the authors say, could help refine the next generation of models used by scientists to try to understand the global impacts of climate change and other major influences.

For example, the authors say there could be a close link between the impacts of eruptions and El Nino and La Nina weather phenomena, which trigger droughts or floods in parts of Asia and Australia.

Strong El Nino or La Nina episodes could counteract the impact of eruptions, lessening their drying and moistening effects, or under certain conditions exacerbate the impacts to create devastating droughts or floods.

The authors also say their study serves as a warning for possible unintended impacts of massive "geo-engineering" projects to fight climate change, such as building artificial volcanoes to cool temperatures by pumping sulphate particles in the upper atmosphere.

(Editing by Daniel Magnowski)

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