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The Tambora volcano in a satellite image from June 3, 2009.

The 1815 eruption of the Tambora volcano (pictured on June 3, 2009) in Indonesia did not cause global cooling in the early 1800s. Instead a newly detected 19th-century volcanic eruption—whose location is still a mystery—was the culprit, scientists said in December 2009.

Photograph courtesy NASA

John Roach

National Geographic News

Published December 10, 2009

A newly detected 19th-century volcanic eruption may solve the mystery of a strangely cool decade in the early 1800s, researchers say—but the location of the volcano itself remains a puzzle.

Scientists have long blamed the 1815 eruption of an Indonesian volcano, Tambora, for a worldwide cold snap the following year—the so-called year without a summer.

But the entire decade from 1810 to 1819 was about 0.9 degree Fahrenheit (0.5 degree Celsius) cooler than normal—making the dip in temperatures prior to Tambora a mystery.

Now the case appears to be closed: A recent analysis of ice cores from Greenland and Antarctica reveal that in 1809, a volcano somewhere in the tropics erupted, a new study says.

Geologic evidence for an eruption has yet to be found, and scientists don't even know where the earlier eruption occurred, said study leader Jihong Cole-Dai, an environmental chemist at the South Dakota State University in Brookings.

But they do know it happened somewhere in the tropics, Cole-Dai added.

That's because only the tropics' particular wind patterns are able to carry volcanic material so thoroughly around the world.

Coldest Decade

In ice cores dating to 1809 and 1810, scientists found high concentrations of sulfuric acid, which forms when eruptions spew sulfur dioxide into the stratosphere.

When in the air, the expelled bits of sulfuric acid scatter and reflect sunlight, Cole-Dai said.

"That reduces the amount of energy that actually comes into the Earth's and that helps to cool the planet," Cole-Dai said.

The amount of sulfuric acid found in ice cores from Earth's poles suggests the eruption was about half the size of Tambora's, which spewed about a hundred megatons of sulfur dioxide into the lower atmosphere.

"Even half of that, 50 megatons, would still be very large," Cole-Dai said.

The newfound eruption ushered in the coldest decade in the past 500 years, he added.

(Related: "Ancient Global Dimming Linked to Volcanic Eruption.")

Sulfur Solution to Global Warming?

Some scientists have suggested injecting sulfur into the lower atmosphere to combat global warming.

"That geo-engineering idea is based on how we understand volcanic eruptions cool the Earth," Cole-Dai said.

Since the sulfur largely disappears from the atmosphere after a few years, however, such a solution would require continuous inputs of sulfur—which in turn could spell trouble for the environment, he noted.

"The sulfur you put in there will come down as sulfuric acid, and that's generating acid rain."

Findings reported October 25 in Geophysical Research Letters.

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