Little ice age holds big climate clues

By Environmental News Network staff

March 1, 2000

Web posted at: 12:43 p.m. EST (1743 GMT)

Chemical signals from two of the largest volcanic eruptions in human history have allowed scientists to refine the chronology of an ice core taken from a Wyoming glacier. The refined chronology indicates an abrupt end to the little ice age.

"Now that we have documented a quick climate change in the past, there is no

reason not to believe it can occur in the future," said Paul Schuster, a hydrologist with the U.S. Geological Survey in Boulder, Colorado.

Previous climate data revealed that a centuries-long cold snap - the little ice age - ended in the mid-1800s. But scientists had not documented how quickly the cold spell ended.

Ice-core data gathered by Schuster and colleagues and reported in the Feb. 27 Journal of Geophysical Research shows that the little ice age ended over a span of 10 years, most likely in three to four years.

"That is a major climatic shift in what we consider a quick period of time," said Schuster.

Data with an error of plus or minus 10 years is not generally expected from ice cores taken from mid-latitudes such as the Rocky Mountains in North America. Melt water associated with warmer temperatures tends to corrupt the ice layers.

The scientific community criticized a paper published in 1996 on this ice core taken from Upper Fremont Glacier in the Wind River Range because it had an error bar of plus or minus 100 years.

"The data was sensible, but the error bar was huge," said Schuster. "In the scientific community, that doesn't wash well."

To refine the chronology, the researchers used a technique known as electrical conductivity measurement. The method employs two tiny electrodes to get a detailed reading of the acidity of the ice.

Volcanic eruptions emit gases and minerals into the air that make precipitation more acidic. As a result, the signatures of volcanic eruptions are recorded in ice cores.

The two largest volcanic eruptions in human history occurred in the Indonesian islands - in 1815 at Tambora and 1883 at Krakatau. The researchers detected the signatures of these eruptions in the Wyoming ice core, giving them new data to refine their error bar to plus or minus ten years.

"With that kind of resolution you can say things," said Schuster.

The researchers hope this refinement will give mid-latitude ice cores credence in the scientific community and encourage missions to retrieve more mid-latitude cores.

"Because we are in a global warming, these glaciers are going away," he said. Recent studies suggest that glaciers in Glacier National Park in Montana and Canada will disappear within 50 years.