Sea levels have been rising in parts of the Indian Ocean partly as a result of human-induced increases of atmospheric greenhouse gases, a new study shows.

The study, led by researchers at the University of Colorado (UC) at Boulder, combined sea surface measurements going back to the 1960s and satellite observations.

The findings indicate that anthropogenic climate warming likely is amplifying regional sea rise changes in parts of the Indian Ocean, threatening inhabitants of some coastal areas and islands, said associate professor Weiqing Han of UC Boulder, the lead study author.

The sea level rise, which may aggravate monsoon flooding in Bangladesh and India, could have far-reaching impacts on both future regional and global climate, according to the study.

Along the coasts of the northern Indian Ocean, seas have risen by an average of about 0.5 inches, or 13 millimeters, per decade.

The key player in the process is the Indo-Pacific warm pool, an enormous, bathtub-shaped area of the tropical oceans stretching from the east coast of Africa west to the International Date Line in the Pacific. The warm pool has heated by about one degree Fahrenheit, or 0.5 degrees Celsius, in the past 50 years, primarily caused by human-generated increases of greenhouse gases.

"Our results from this study imply that if future anthropogenic warming effects in the Indo-Pacific warm pool dominate natural variability, mid-ocean islands such as the Mascarenhas Archipelago, coasts of Indonesia, Sumatra and the north Indian Ocean may experience significantly more sea level rise than the global average," said Han.

While a number of areas in the Indian Ocean region are showing sea level rise, the study also indicated that the Seychelles Islands and Zanzibar off Tanzania's coastline show the largest sea level drop.

Global sea level patterns are not geographically uniform, and sea rise in some areas correlate with sea level fall in other areas, the researchers said in the study, published in this week's issue of Nature Geoscience.

"Our new results show that human-caused 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," the researchers wrote.

The Indian Ocean is the world's third largest ocean and makes up about 20 percent of the water on Earth's surface. The ocean is bounded on the west by East Africa, on the north by India, on the east by Indochina and Australia, and on the south by the Southern Ocean off the coast of Antarctica.