Posted 5 January 2016
Ever wondered what causes the global-average warmth during El Nino? Dr Roy Spencer explains it here: "The sun's energy is the ultimate source of energy for the climate system, but it really doesn't explain why El Nino years are unusually warm...or why La Nina years are unusually cool. The answer lies in the circulation of the Pacific Ocean, more specifically the vertical circulation of that ocean basin.
"The short answer is that, during El Nino, there is an average decrease in the vertical overturning and mixing of cold, deep ocean waters with solar-heated warm surface waters. The result is that the surface waters become warmer than average, and deeper waters become colder than average. The opposite situation occurs during La Nina.
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