Originally posted here.

La Niña can contribute to more hurricanes in the North Atlantic and drier conditions in the southern United States.Credit…NOAA, via Associated Press

El Niño is back.

In July, the World Meteorological Organization announced that conditions for the cyclical climate phenomenon had developed in the tropical Pacific, confirming a similar announcement from the National Oceanic and Atmospheric Administration in June. El Niño conditions release additional heat into the atmosphere and are associated with warmer years on average.

Here’s a basic guide to help you sort out what they are talking, or not talking, about.

They are both intermittent climate phenomena that originate in the equatorial Pacific Ocean but can have wide-ranging effects on weather around the world.

The two are related: They are the opposite phases of what is called the El Niño-Southern Oscillation, or ENSO. Thus they can never occur simultaneously. And there are plenty of times when neither occurs.

ENSO describes the fluctuation of two things in the equatorial Pacific: the surface temperature of the ocean and the pressure of the air above it.

The temperature component is pretty straightforward, and most news reports focus on it. When sea-surface temperatures are above average by about 1 degree Fahrenheit or more, El Niño can develop. When temperatures are below average, La Niña can form. When temperatures are at or near average — what’s called ENSO-neutral — neither develops.

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