evidence: El Niño and La Niña alternately warm and cool large areas of the tropical Pacific—the world’s largest ocean—which significantly influences where and how much it rains there. The primary location of moist, rising air (over the basin’s warmest water) is centered over the central or eastern Pacific during El Niño and over Indonesia and the western Pacific during La Niña. [...] During El Niño, when the trade winds are weak or even occasionally reverse themselves, the amount of cold water that comes to the surface is reduced. Warm waters in the west Pacific Ocean slosh to the east. Now there is a large area along the equator where ocean temperatures are above normal. Heat from the ocean then goes out into the atmosphere, leading to warmer air temperatures in the Pacific and subsequently, to warmer global air temperatures (plus a cascade of other impacts). [...] Weak winds allow warm surface waters to build up in the eastern Pacific. Sometimes, but not always, the atmosphere responds to this warming with increased rising air motion and above-average rainfall in the eastern Pacific. This coordinated change in both ocean temperatures and the atmosphere begins an El Niño event. As the event develops, the warmed waters cause the winds to weaken even further, which can cause the waters to warm even more.