The seasons, which are caused by the tilt of the Earth’s axis, are the most important periodic fluctuations in climate. But changes in atmospheric and oceanic circulation pat-terns also cause periodic changes in climate on a global scale. The best known is El Niño– Southern Oscillation (ENSO), which originates in the Pacific Ocean but creates effects around the world. Less well known is the North Atlantic Oscillation, which affects the climates of northern Europe and the Maritime Provinces in Canada.
Every two to seven years, the El Niño phenomenon causes atmospheric pressure over the western Pacific Ocean to rise. The equatorial ocean currents that usually flow westward reverse themselves, and the normally cold waters off the coasts of Peru and Chile are replaced with warmer water. This prevents cold, nutrient-rich water from welling up, ruining coastal fishing. It typically happens around Christmastime, hence the name El Niño, or the Christ child.
Topic: Earth Science
Subtopic: Climate/Climate Change
Keywords: Climatology, Ocean temperature, Ocean circulation, Ocean-atmosphere interaction, Weather, El Nino Current, Droughts, Rain and rainfall