Spring 2010 saw an enormous swing from El Niño to La Niña. Flooding in Indonesia, Colombia, and Australia has all been tied to this phenomenon.
El Niño and La Niña represent opposite extremes in the naturally occurring climate cycle referred to as the El Niño/Southern Oscillation (ENSO). They are associated with opposite extremes in sea-surface temperature across the Pacific, and with opposite extremes in rainfall, surface air pressure, and atmospheric circulation from Indonesia to South America (approximately half the distance around the globe).
Only 1973, 1983, and 1998 have seen larger within-year swings than 2010.