The 2011 La Niña was so strong that it caused global mean sea level to drop by 5 millimeters, a new study shows. Since the early 1990s, sea level has been rising by about 3 millimeters per year, satellite data show. But between the beginning of 2010 and the middle of 2011, sea level fell by 5 millimeters. This occurred concurrently with the La Niña phase of the El Niño– Southern Oscillation (ENSO). ENSO involves a shift in ocean surface temperatures in the tropical Pacific and changes in precipitation patterns around the world. Previous studies have shown that strong El Niño events can increase sea level temporarily.