Sea-level increases may be worse for some areas than others
Sea levels are rising, but not in a geographically uniform pattern, says a new study published online on July 11 in the journal Nature Geoscience.
Focusing on the Indian Ocean, researchers from the University of Colorado and the National Center for Atmospheric Research, both in Boulder, found that increases in sea levels in some regions corresponded with declines in other areas.
Sea level increases were significantly greater than the global mean at midocean islands such as the Mascarenhas Archipelago as well as the coasts of Indonesia and Sumatra and the northern Indian Ocean.
Conversely, the Seychelles islands and the coasts of Kenya and Tanzania showed the largest sea level drops.
Conventional understanding of sea level changes has been explained by the melting of glaciers and polar ice caps. However, the study, which combined satellite observations and historical sea-surface measurements, found that other human-induced environmental alterations, such as changes in atmospheric wind patterns and rising ocean temperatures, were significantly modifying sea level patterns.
“Sea level rises in the Indian Ocean cannot be explained by the melting of continental ice,” said coauthor John Fasullo, a scientist at the National Center for Atmospheric Research. “We found that it is the interaction between wind patterns and warmer ocean temperatures that have led to this disproportionate rise in ocean levels.”
The Indo- Pacific pool, an enormous bathtub-shaped area stretching between the eastern coast of Africa and the international date line in the Pacific Ocean, was identified as the key player in influencing the sea level changes in the Indian Ocean. The pool holds the warmest seawaters in the world and dictates the circulation patterns for the Indian Ocean. Over the last 50 years, the pool has warmed by about 1 degree Fahrenheit, primarily because of human-generated greenhouse gases.
“In a sense, this whole process is … triggered by the increasing water temperatures,” Fasullo said. “When that happens, we see a change in the wind patterns, which is then what leads to the regionally disproportionate sea levels.”
Increases in sea levels have been a trend since the 1960s. While decreases in sea levels do not have any adverse effects on residents in such areas, the researchers speculate that the ongoing increases in sea levels could have future effects on regional and global weather. The most immediate effect is predicted to be increased monsoon flooding in Bangladesh and India and erratic regional rainfall. But how these changes might unfold over time is unknown, the authors said.
