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La Niña from space

A La Niña year is part of the earth’s natural cycle, but if it’s strong enough the consequences can be disastrous. Photo: Unsplash/NASA

The Inertia

Australia’s Bureau of Meteorology issued an official “La Niña watch” on May 14. It came after the tropical Pacific Ocean started showing signs indicative of a coming cooling pattern. The Bureau was quick to clarify that it is not declaring that a La Niña event is underway, but that there is a decent chance of one soon.

“While conditions in the tropical Pacific Ocean are currently neutral,” Bureau officials wrote, “there are some signs that a La Niña may form in the Pacific Ocean later in 2024. It is important to note, however, that there is a similar likelihood that the tropical Pacific Ocean will remain neutral.”

La Niña is a period of periodic cooling of the ocean’s surface in the central and east-central equatorial Pacific. It’s the cooling phase of the El Nino/Southern Oscillation (ENSO) cycle. These events occur every 3-5 years (or so), but once in a blue moon, we’ll have them back to back. When they occur in three consectutive years, it’s a phenemenon known as a “triple dip.

The announcement comes after researchers studying sea surface temperatures saw that sea surface temperatures in the central Pacific have been steadily cooling since December 2023. In the past, similar conditions have led to a La Niña event about half of the time.

Despite the fact that La Niña is caused by cooler temperatures in the central and eastern tropical Pacific Ocean, it has global ramifications. It can impact “everything from wind, temperature, and rainfall patterns to the intensity of hurricane seasons and even the distribution of fish in the seas,” according to IFLScience.

El Niño phases generally mean hotter global average temaperatures — part of the reason we’ve seen so many temperature records broken in recent years — but as the world warms, even La Niña phases aren’t enough to stop those weirdly hot averages.

“The past year – 2023 to 2024 – has been marked by a particularly strong El Niño phase,” IFLScience wrote. “The warmer waters cause the Pacific jet stream to move south and extend, causing drier and warmer weather to hit northern parts of the US and Canada, but wetter weather in southern states. Over in Australia, El Niño typically promotes hotter temperatures, as well as reduced rainfall in the east and north of the country.”

From 2020 to 2023, however, we saw one of those rare triple-dips. That resulted in drier weather in the southern US, but notably wetter and colder weather in the Pacific Northwest and Canada. For Australians in particular, a strong La Niña event can lead to catastrophic flooding like they saw in 2021.


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