Warming in the southern hemisphere of Asia has a stronger affect on monsoon strength than scientists previously thought, a discovery that could have a devastating affect billions of people, according to a new study.
A team of researchers from Georgia State University, GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany, Woods Hole Oceanographic Institution and Brown University rebuilt the eastern Indian Ocean's precipitation history by examining ancient sediment core from the eastern Indian Ocean.
Each year, between June and September, the South Asian Monsoon dumps heavy rainfall on the region. A half year of drought and a negative economic, social and environmental impact for India, Nepal, Bangladesh, Bhutan, Pakistan and Sri Lanka follow the downpour.
The monsoon's unpredictable rainfall and wind patterns can lead to landslides and floods that wreak havoc on the agriculture and food supply of people in the southern Asia region.
Pressure and temperature differences between the continent of Asia and the subtropical Indian Ocean create the South Asian Monsoon.
Previous reconstructions of the monsoon's history used sediment cores from two climate archives: the Arabian Sea and Chinese cave stalagmites. The researchers learned that only the stalagmite examination rendered any correlative data on East Asian Monsoon precipitation patterns.
"However, we were only able to associate 30 percent of the variability of monsoon precipitation in the eastern Indian Ocean with fluctuations in the Earth's axis inclination," Dr. Daniel Gebregiorgis, lead author of the study and a researcher at Georgia State University, said in a press release. "This means that it only plays a subordinate role in the fluctuations of the monsoon."
The team discovered a more complicated stimulus than scientists once assumed for the South Asian Monsoon's wind and precipitation patterns.
"Using this, we have been able to reconstruct precipitation in the eastern Indian Ocean for the past one million years," said Ed Hathorne, a researcher at GEOMAR Helmholtz Centre for Ocean Research Kiel and co-author of the study.
Scientists once thought solar insolation brought on by the shifting in Earth's axis in the northern hemisphere brought on monsoon pattern irregularity in the southern hemisphere.
Though the team of international researchers has made great strides in figuring out more about the monsoon's patterns, they know they still have a long way to go.
"The evaluation of the new climate archives shows that we have still not fully understood the monsoon," said Martin Frank, a researcher at GEOMAR Helmholtz Centre for Ocean Research Kiel. "As long as this is not the case, it is difficult to estimate the reactions of this important climate system to a globally warming atmosphere."
Researchers published the study Thursday in the journal Nature.