Volcanic eruptions affect rainfall over Asian region

WASHINGTON - Large volcanic eruptions affect rainfall over the Asian monsoon region where seasonal storms water crops for nearly half the population of the earth.

The eruptions are also believed to affect the weather by spewing particles that block solar energy and cool the air.

Tree-ring researchers from the Columbia University’s Lamont-Doherty Earth Observatory showed that big eruptions tend to dry up much of Central Asia, but bring more rain to southeast Asian countries like Vietnam, Laos, Cambodia, Thailand and Myanmar - the opposite of what many climate models predict.

Some suspect that extended “volcanic winters” from gigantic eruptions helped kill off dinosaurs and Neanderthals, the journal Geophysical Research Letters reported.

The growth rings of some tree species can be correlated with rainfall. Tree Ring Lab used tree rings from some 300 sites across Asia to measure the effects of 54 volcanic eruptions going back about 800 years.

The data came from the observatory’s new 1,000-year tree-ring atlas of Asian weather which has produced evidence of long, devastating droughts, according to a Columbia University statement.

“We might think of the solid earth and the atmosphere as two different things, but everything in the system is interconnected,” said Kevin Anchukaitis, the paper’s lead author. “Volcanoes can be important players in climate over time.”

Large explosive eruptions send up sulphur compounds that turn into tiny sulphate particles high in the atmosphere, where they deflect solar radiation. The resulting cooling on the earth’s surface can last for months or years.

Not all eruptions have that effect, however. For instance, the continuing eruption of Indonesia’s Merapi this fall has killed dozens, but this latest episode is probably not big enough by itself to effect large-scale weather changes, scientists believe.