how is el nino caused?

Answer 1

Warm water off the west coast of south America moves closer to Australia, causing the global weather patterns to change, because the ocean temperature changes, so does the air temperature and so forth.

This has some good diagrams:
http://en.wikipedia.org/wiki/El_nino

Think of it as a hot cup of coffee, you see the steam coming up from it, now move the cup, you move the steam. The same thing happens with El Nino, but on a larger scale, causing a lot of other things to shift because the globe is interconnected, the phenomenon isn't localized.

Answer 2

by the warm air from the pacific meeting with the cold air from the arctic

Answer 3

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