The Indo-Pacific warm pool, shown in bright orange, heated by 0.5C in the past 50 years (Image courtesy NASA Earth Observatory)
'Uneven' sea level rises are posing a threat to densely populated coastal areas around the Indian Ocean, according to researchers.
Sea levels have risen across the world as a result of thermal expansion of the ocean (water expands as it heats up) and as melting ice adds more water volume.
However, researchers from the National Center for Atmospheric Research (NCAR) and the University of Colorado have shown that the rises are not uniform across the world and are affected by other changes in atmospheric or oceanic currents.
In the Indian Ocean this has resulted, since the 1960s, in substantial decreases in sea levels in the south tropical region, including the Seychelles Islands and the island of Zanzibar off Tanzania.
In contrast, sea level rises have been much higher along the coastlines of the Bay of Bengal, the Arabian Sea, Sri Lanka and the Indonesian islands of Sumatra and Java.
In a study published this week in the journal Nature Geoscience, which could have implications for how scientists predict sea level changes, the authors blame complex atmospheric wind patterns for the uneven rises.
'Complex circulation patterns in the Indian Ocean may also affect precipitation by forcing even more atmospheric air than normal down to the surface in Indian Ocean subtropical regions,' says co-author Weiqing Han.
'This may favor a weakening of atmospheric convection in subtropics, which may increase rainfall in the eastern tropical regions of the Indian Ocean and drought in the western equatorial Indian Ocean region, including east Africa.'
The study concludes that if human-caused global warming continues then the pattern they detected was, 'likely to persist and to increase the environmental stress on some coasts and islands in the Indian Ocean'.
Useful links
Patterns of Indian Ocean sea-level change in a warming climate
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