The exposure of Kiribati to changes in sea levels is exacerbated by the Pacific decadal oscillation, which is a climate switch phenomenon that results in changes from periods of La Niña to periods of El Niño. This has an effect on sea levels. For example, in 2000, there was a switch from periods of downward pressure of El Niño on sea levels to an upward pressure of La Niña on sea levels, which upward pressure causes more frequent and higher high tide levels. The Perigean spring tide (often called a king tide) can result in seawater flooding low-lying areas of the islands of Kiribati.