El Niño happening more as climate warms

El Niño and La Niña events are expected to increase in frequency and intensity as a result of climate change, according to a new review.

The review, carried out by an international team of scientists and published in Nature Earth & Environment, synthesises a range of different models to make predictions about the El Niño Southern Oscillation (ENSO).

“The most fundamental point is that the variability of ENSO is increasing in response to anthropogenic greenhouse emissions,” says Dr Wenju Cai, director of the Centre for Southern Hemisphere Oceans Research at CSIRO, and lead author on the paper.

This means that the El Niño and La Niña fluctuations are getting more intense, and becoming more frequent.

ENSO is the fluctuations in sea surface temperature in the southern Pacific Ocean. During the El Niño phase of the cycle, there are warmer waters and thus more precipitation on the eastern side of the Pacific Ocean, and drier conditions on the western side. During La Niña, the opposite happens, causing less precipitation in the Americas and more in Australasia.

“You’ve got two extremes: more severe drought and more frequent drought, and more severe floods and more frequent floods,” says Cai.

In Australia, El Niño events are associated with droughts, and La Niña with floods and cyclones, but the effects reach well beyond this country. The authors point out, for instance, that a 1998 La Niña event coincided with floods in China that led to the deaths of thousands of people, and the displacement of over 200 million, as well as the flooding of more than 50% of Bangladesh’s land.

According to Cai, extreme El Niño events happened roughly once every 20 years in the 20th century, but they’re now increasing in frequency. “It will almost double, to one in 11 years or so.”

He adds that there’s more consensus among the models they’ve examined than in previous studies, such as one he authored in 2015. “More models are saying the same thing. I think that it’s because we are now able to get more realistic models.”

The consensus among these models is that ENSO variability and magnitude will increase, if climate change continues unchecked.

“Time is running out to avoid catastrophic consequences,” says Cai.

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