Rising seas –  of 2 feet, five feet, or even 7 feet –  have been a topic of much speculation. And knowing answers matter. How far should communities plan to back away from the ocean? What size dams are needed? How many people are in danger?

Further complicating the science is the fact that global sea level rise isn’t actually global. The seas don’t rise uniformly everywhere. Changes in oceanic and atmospheric circulation impact regions differently, causing some places to be hit with higher watermarks than others.

Take for example the Seychelles Islands and Zanzibar off the coast of Tanzania. These islands in the southwest Indian Ocean are actually experiencing sea level decrease.

But in the North, along the Bay of Bengal, Sri Lanka, and Java are getting hammered as the oceans creep up 5 inches per century, higher than the global mean.

Researchers at the University of Colorado at Boulder published a paper this week in Nature Geoscience that explains a bit more about how sea level in the Indian Ocean works. They investigated for the first time the variable pattern of sea level rise using data from local and satellite observations input into models.

The key player driving these differences is the Indo-Pacific warm pool, a body of water spanning the equatorial Pacific to the eastern Indian Ocean. It’s the warmest ocean water in the world, and it’s been getting warmer due to human-induced global warming.

That’s set off changes in surface wind patterns over the Indian Ocean that impacts rainfall and sea levels in eastern areas.

Oddly enough, the Maldives, well known these days as the first country to be subsumed by climate change, is actually in an area of sea level retreat, according to the study.

How can that be? The researchers explain that sea level rise occurs there during the winter and because the Maldives is so low in elevation, it’s still heading underwater.

-Alison Hawkes