Increase in Indian Ocean levels could threaten millions: new study
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Levels are rising unevenly in the Indian Ocean putting millions at risk along low-lying coastlines in Bangladesh, Indonesia and Sri Lanka, besides worsening monsoon flooding in India, say scientists in a new study
Rising levels in parts of the Indian Ocean could endanger millions of people living along low-lying coastlines, and worsen monsoon flooding in India and Bangladesh, says a study led by Weiqing Han, associate professor in atmospheric and oceanic sciences at the University of Colorado, US.
The study, involving researchers from the University of Colorado and the National Centre for Atmospheric Research, attributes the rising levels to climate change triggered by warming seas and changes in atmospheric circulation patterns.
The team of researchers, in their study published in the latest issue of the journal Nature Geoscience, used long-term tide gauge data, satellite observations and computer climate models to build a picture of sea level increases in the Indian Ocean since the 1960s.
They found that sea level rise is particularly high along the coastlines of the Bay of Bengal and the Arabian Sea. Bangladesh, Sri Lanka, Sumatra and Java could suffer rises greater than the global average.
Sea levels in general are rising globally by about 3 mm (0.1181 inches) a year. But along the coasts of the northern Indian Ocean, seas have risen by an average of about 0.5 inches, or 13 mm, per decade, the study notes.
Scientists also found that sea levels in other areas are falling. The study indicates that the Seychelles Islands and Zanzibar, off the coast of Tanzania, show the largest sea level drop. The key player in the process is the Indo-Pacific warm pool -- an enormous, bathtub-shaped area of tropical ocean stretching from the east coast of Africa west to the International Date Line in the Pacific.
The warm pool has heated up by about 1 degree Fahrenheit, or 0.5 degrees Celsius, in the past 50 years, primarily due to manmade increases in greenhouse gases, says Han. The researchers blame rising temperatures caused by growing amounts of greenhouse gases like carbon dioxide from burning fossil fuels that trap heat in the atmosphere.
Oceans absorb a large part of this extra heat, causing them to expand and sea levels to rise. Warmer temperatures are also causing glaciers and parts of the ice blanketing Greenland and West Antarctica to melt.
“Our new results show that human-caused atmospheric-oceanic circulation changes over the Indian Ocean, which have not been studied previously, contribute to the regional variability of sea level change,” the researchers note in the study.
The two main wind patterns in the region are the Hadley and Walker circulations.
In the Hadley circulation, air currents rise above strongly heated tropical waters near the equator and flow polewards at upper levels, then sink to the ocean in the sub-tropics and cause surface air to flow back towards the equator.
The Walker circulation causes air to rise and flow westwards at upper levels, sink to the surface, and then flow eastwards back towards the Indo-Pacific warm pool.
A strengthening of these two patterns could have far-reaching impacts on the Asian-Australian monsoons, Indonesian floods and drought in Africa, says the study.
Source: Reuters, July 14, 2010
IANS, July 14, 2010
http://sify.com , July 2010