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El Niño and the silent melting of Antarctica

In years with strong El Niño events, the ice shelves that float off the west coast of Antarctica melt faster, even if it snows more than normal. This is the conclusion of a study coordinated by Brazilian geophysicist Fernando Paolo, currently a postdoctoral fellow at NASA’s Jet Propulsion Laboratory. During his PhD at the Scripps Institution of Oceanography at the University of California, San Diego, Paolo and other researchers analyzed the height of the ice shelves off the west coast of Antarctica using satellite images from the last two decades. They found that during strong El Niño periods, characterized by above-average surface water temperatures in the Pacific, the amount of snow deposited on the ice shelves increases as changing wind patterns carry more moisture from the ocean to the frozen continent. At the same time, this wind pattern promotes the flow of warm water toward the continent, which warms up the underneath of the ice shelves and makes the submerged ice melt faster. From 1994 to 2017, the height of the shelves in the region decreased by an average of about 20 centimeters (cm) per year, primarily due to melting of the submerged layers, a process intensified during El Niño events (Nature Geoscience, January 8). “In years with strong El Niño events, two opposing processes occur,” explains Paolo. “The ice shelves lose more mass from basal melting than they gain from increased snowfall.” Melting ice shelves do not directly affect sea level, because they are already floating. But it does regulate the speed at which continental glaciers lose ice into the ocean. “It is important to understand how the ice shelves behave during these weather phenomena, since strong El Niño events will likely become more frequent as the average temperature of the planet increases,” explains Paolo.