Indian Ocean sea levels are rising unevenly, partly due to human-generated greenhouse gas emissions, according to new research published in Nature Geoscience.

The sea-level rise – which puts millions of coastal and island inhabitants at risk – could exacerbate monsoon flooding in Bangladesh and India, and have a significant impact on both the regional and global climates.

The study, which was led by scientists at the University of Colorado at Boulder and the National Center for Atmospheric Research, combined long-term sea-surface measurements with satellite observations and computer models to identify patterns of sea-level change in the Indian Ocean since the 1960s. They found that while sea levels around the Seychelles and Zanzibar have fallen, they have risen elsewhere – particularly in the Bay of Bengal and Arabian Sea, and around the islands of Sri Lanka, Sumatra and Java.

The sea-level changes are being driven by the invigoration of two primary patterns of wind movement, the Hadley and Walker circulations, which is itself partly attributable to rising levels of atmospheric greenhouse gases. ‘Our new results show that human-induced changes of atmospheric and oceanic circulation over the Indian Ocean region, which have not been studied previously, are the major cause for the regional variability of sea-level change,’ said the study’s lead author, Weiqing Han.

The Indo-Pacific warm pool, which spans a large part of the tropical oceans, plays a key role in the process. It has heated by about 0.5°C during the past 50 years, primarily due to human-induced climate change, Han said.

Published in Geographical magazine, September 2010