Just over a year ago, the Earth was coming off of one of the strongest El Niños on record. Waters in the eastern Pacific warmed by El Niño began to cool toward normal in summer and even edged in the opposite direction — as sometimes happens — toward a La Niña.

That cooling reached modest levels through the fall, registering as a weak La Niña. Now, ocean surface temperatures in the eastern Pacific have begun to climb again. In fact, the temperatures have climbed dramatically along the immediate South American coast, reaching 5.4°-7.2°F (3-4°C) above normal just off Ecuador and Peru. This rapid warming played a role in the massive flooding on the South American coast late last month.

Pacific Ocean weekly temperature averages

Pacific Ocean weekly temperature averages. Represented as a difference from normal.

The above-normal water temperatures are expanding westward, which could be a sign of a burgeoning El Niño.

After the other two most recent large El Niño events (in 1982-83 and 1997-98), there was a more prolonged period of below-normal temperatures. Three years passed before El Niño returned after the 1982-83 Niño. Four years passed after the 1997-98 event.

It is still too early to say for certain whether an El Niño will fully take shape later this year. There is still some unusually cool water a few hundred feet below the central Pacific, and warmer water remains in the far western Pacific. These are two factors working against the idea of a rapidly forming El Niño.

However, several computer simulations suggest that despite these influences, El Niño could return this summer and continue into the fall.

For an El Niño to be declared by the National Oceanic and Atmospheric Administration, the water temperature must be at least 0.9°F (0.5°C) above normal in the Pacific region known as Niño 3.4. Those conditions must persist for three months to get the declaration, so it won’t be coming any time soon, but it is worth watching.

Many weather watchers hoped the 2015-16 El Niño would bring beneficial rain and mountain snow to the southwestern U.S., easing the four-year California drought. It largely fell flat in that regard, though.

Ironically, California’s drought was mostly busted this winter when the tropical Pacific was near neutral, underscoring that while El Niño is an important climate player, it’s not the only one.

There are suggestions that the strongest El Niños could become more common as the world warms. But even if the frequency of El Niños does not change as much, there is still much to be understood about how climate change will affect the El Niño and La Niña cycle.