Extreme storm surges are much more common today than they used to be. © Moorefam/ iStock Extreme storm surges are occurring twelve times more frequently today than in 1900, new analyzes show. Accordingly, such “floods of the century” only occurred once every 100 years back then, but today they occur on a global average every eight years. The main causes of the increasingly extreme storm surges are man-made climate change and sea level rise, as climate researchers have determined.