Is sea level rise happening now? Where?
Is sea level rise the same all over the world, as if we're filling a giant bathtub?
No. Sea level rise is uneven. In some regions of the ocean it has gone up by 12-15 millimeters per year (about half an inch per year) between 1993 and 2015, and in some regions it has gone down by that amount. But on average, it has gone up by about 3 millimeters per year (about 28 millimeters, or 1-1/8 inches, per decade) in that same period. The reason is that regional climate cycles like El Niño (and longer-term effects like the Pacific Decadal Oscillation) change ocean circulation, which changes sea level.
How does El Niño fit into the sea-level rise picture?
Over periods of 2-8 years, after removing the overall trend of about 3 millimeters per year, the globally averaged sea-level rise closely follows the waxing and waning of El Niño. The main reason for this close match is that El Niño shifts rainfall from land to ocean, raising sea level. Its opposing phase, La Niña, shifts rainfall to land, causing sea level to drop.
How much rise should we expect from Greenland and Antarctica?
Currently the total sea level rise is about 3 millimeters per year (about 1/8 of an inch per year). Of that amount, about one-third comes from Greenland and Antarctica, one-third from glaciers like those in Alaska or the Himalayas, and one-third from the expansion of seawater as it warms up. In the future, we expect Greenland and Antarctica will contribute larger amounts.