- This year's El Niño could be the most severe on record, according to some projections
- El Niños can cause extreme and often devastating weather events around the world
(CNN)If you're wondering why you're still wearing shorts in winter, meteorologists have a two-word answer: El Niño.
What is El Niño and what causes one?
What happens when there's an El Niño?
(Swipe right to see ocean conditions in July 1997; swipe left to see July 2015)
Will this El Niño be worse than 1997?
The Oceanic Niño Index (ONI) measures sea surface temperatures in the tropical Pacific. Zero is average, positives numbers are warmer, and negative numbers are colder. Anything above 0.5 is considered El Niño conditions -- and anything above 1.5 is a strong El Niño.