What are El Niño and La Niña and how do they affect temperatures?
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Nearly 100 million people in the U.S. will face triple-digit temperatures by the end of the week as a massive heat wave moves across the southwestern U.S. Reoccurring weather phenomena are playing a critical role in the scorching heat, and could be a contributor to it getting worse. El Niño and La Niña — opposing extremes that cycle with each other as sea surface temperatures, rainfall, air pressure and atmospheric circulation vary — play a major role in global temperatures. What is El Niño? This year marks the return of El Niño , a natural climate phenomenon that develops every two to seven years when the Pacific Ocean experiences "warmer-than-average" surface temperatures. NOAA explains that the event weakens trade winds as warm water is pushed toward the west coast of the Americas, causing the Pacific jet stream to move south. This transition causes the northern U.S. and Canada to experience dryer and warmer weath...