What Is El Niño and How Does it Affect Weather Around the World?

Here’s what can happen when the surface of the equatorial Pacific gets just a little warmer: Thousands of people die as the weather changes from India to Florida. Some economies lose billions of dollars; others enjoy respite from weather-related losses. Prices of commodities such as coffee and cocoa jolt skyward. Then when the waters cool, patterns shift, with areas previously spared often experiencing calamitous hurricanes, floods or drought, and others getting a break from such buffeting forces. The whole cycle is known as El Niño-Southern Oscillation. It is made up of El Niño, the Pacific’s warm phase; La Niña, the cold side; and a neutral phase in between. The US declared that the whole thing kicked off again in June, and Australia, which uses different criteria, concurred on Sept. 19.

El Niño’s impact on weather in the Northern Hemisphere tends to be muted in the summer and autumn. In the Atlantic, it can produce wind shear, a sudden change in wind velocity or direction, which can halt hurricane season there; record warm ocean temperatures, however, have made for a busy storm season. The El Niño is expected to persist through February. An El Niño usually means heavy rain along the Pacific coast of the Americas, from California to Chile and across to Argentina. That could be good news for Argentina, where a record drought has worsened the country’s economic troubles. On the other hand, the last big El Niño in 2015-16 brought deadly winter floods to the US Midwest. El Niño typically produces dry weather in Australia, Indonesia, the Philippines and northern Brazil. The last time, it reduced rainfall in the Indian monsoon, parching farmlands, and curbed production of cocoa in Ivory Coast, rice in Thailand and coffee in Indonesia. There were wildfires in Australia and South Africa.