DATA SOURCE Melting glaciers and ice sheets, including those in the Arctic, are the main reason sea levels increased between 2006 and 2018. Oceans, which rose by 20 millimetres (0.79 inches) between 1901 and 2018, are now rising by almost four millimetres (0.16 inches) per year. Higher oceans, combined with more intense storms and rain, are expected to cause more catastrophic flooding in coastal cities around the world.