Asian monsoons have been intensifying over the last 400years, and they're only going to get worse. Stronger monsoonrains will cause severe flooding and erosion, affecting halfthe world's population.
The South Asian monsoon carries rain to billions of peoplein India, China, Bangladesh, and other countries. Themonsoon season begins in summer when northeast trade windsreverse direction and carry water-saturated air towards theland. "The South Asian monsoon . . . is key to agricultureand water resources," says Gerald A. Meehl of the NationalCenter for Atmospheric Research. "The past and futurebehavior of the monsoon is therefore of critical interest."
Researchers have studied changes in monsoons over tens ofthousands of years, but few of them have looked at howthey?ve affected human civilizations. Now researchers in theU.S. and India are using the fossil record to learn aboutvariations in monsoon strength in the past.
David M. Anderson of the University of Colorado looked atthe microscopic, hard-shelled fossils called Globigerinabulloides in sediments of the Arabian Sea. Monsoon windsblow along the coasts of Saudi Arabia and Oman and churn updeep waters, transporting minerals to the surface. In yearswhen monsoon winds are strong, G. bulloides has a populationboom and more shells end up in the sediments on the ocean floor.
By searching the fossil records, researchers accumulated a1,000-year record of the fossils' abundance and monsoonintensity. The results show that since 1600, there has beena steady increase in monsoon intensity, with a greaterincrease during the last 100 years, which may be due toglobal warming. In Asia, global warming may create a greatersummertime difference between land and ocean temperatures,which would increase monsoon intensity.
Increased monsoon intensity means less drought, but it canalso create the kind of flooding and erosion that damagesthe livelihood of millions, such as in the recent floodingin Bangladesh. Global warming may affect some areas for thebetter and others for the worse, but one thing it does bringis change?and we don?t yet know what kind of change it willbring.
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