Monsoon strength has grown in 400 years

BOULDER, Colo., July 25 (UPI) -- India's monsoon rains have become stronger over the past 400 years as Earth warmed gradually following the Little Ice Age, government researchers report in a paper in Friday's issue of the journal Science.

The finding could have policy implications for governments worldwide as they attempt to deal with the challenges of global warming.

"We're trying to get a handle on natural variability that would be there in the absence of humans doing anything," David Anderson, the paper's lead author and a researcher with the Paleoclimatology Program of the National Oceanographic and Atmospheric Administration in Boulder, told United Press International. Paleoclimatology is the attempt to understand ancient climates by studying fossil records and other geological markers.

Nearly half the world's population depends on these rains to provide water for growing crops, the paper said. Understanding factors governing the monsoon is important in determining the way it is affected by changes in climate.

"We like to use these 'paleo' records to get a measure of how much natural variability there is in the system," Anderson said.

The monsoons originate when hot winds blow across the Arabian Sea, between the Arabian Peninsula and India, engorging the atmosphere with moisture that rains down on the land. The mechanism also creates an upwelling of nutrient-rich waters from the sea bottom, Anderson explained. Other research has found stronger winds and stronger upwelling of waters lead to the presence of large numbers of fossilized shells of a microscopic animal called Globigerina bulloides.

By analyzing sediment cores from the Arabian Sea and using carbon dating methods, Anderson and colleagues linked increases in the abundance of these shells with the gradual warming of Earth over the past 400 years. He noted, however, no records exist to demonstrate the monsoon rains actually have increased over this period. Climatologist Jonathan Overpeck of the University of Arizona in Tucson, a co-author, plans to obtain rainfall records for the past 10,000 years from Asia by analyzing the chemistry of lake beds.

Nevertheless, the findings are important in understanding climate change, David Black, a specialist in ancient climates at the University of Akron, Ohio, told UPI.

"One of the things the Anderson paper did is it provided pretty good baseline record of climate variability for a climate system that affects a staggering number of people every year -- but one that we didn't have a background for," said Black, whose commentary accompanies the paper.

"What's really an important part of understanding the current situation is to try to understand the mechanisms and how the climate system responds to the different factors in the previous several hundred years," said Gerald Meehl, a climatologist at the National Center for Atmospheric Research in Boulder.

The question remains, however, is Earth's warming over recent decades is the result of human activity, as many scientists argue, or is it the result of the natural emergence of Earth from the Little Ice Age?

"Unfortunately, the Anderson paper can't quite get at that question," Meehl said.

(Reported by Harvey Black, UPI Science News, in Madison, Wis.)