The current El Ni帽o is already the strongest on record and is forecast to get even stronger, peaking around November or December. Though it should be over by June next year, the effects of this monster event will continue to be felt long after that.
鈥淚 expect that this super El Ni帽o event will drive multiple climate regime shifts like we鈥檝e seen after past super El Ni帽o events,鈥� says hurricane specialist . 鈥淩egime shifts tend to cause considerable trouble 鈥� significant disruptions to ecosystems and to the humans that depend on them.鈥�
For instance, this El Ni帽o is expected to lead to a devastating drought in the Amazon that could kill off some of the remaining areas of rainforest. This would release huge quantities of carbon dioxide and also make the whole region permanently drier, because much of the rainfall in rainforests comes from the water evaporating from trees.
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El Ni帽os occur when warm water that has built up in the western Pacific spills east across the equator, making the surface of the eastern Pacific warmer than usual. An El Ni帽o is said to be happening when the sea-surface temperature in one region along the equator is 0.5掳C above average; at the time of writing, it is 3.4掳C and climbing.
One reason why El Ni帽os end is that the warm water that spreads across the Pacific slowly disperses. Some of it flows away from the equator and the water also cools as it transfers vast amounts of heat to the atmosphere, which leads to a sudden jump in global surface temperatures.
This year鈥檚 average temperature is on track to tie with 2024鈥檚 at around 1.6掳C above the pre-industrial level, and 2027 is or more. The next year could be a bit cooler if a La Ni帽a makes the Pacific soak up more heat than usual, but we are on the brink of permanently crossing the 1.5掳C threshold we were meant to avoid.
What happens below the surface of the Pacific also plays a key role in bringing about the end of El Ni帽os. For instance, the arrival of warm water in the eastern Pacific triggers gigantic underwater waves known as Rossby waves that travel westwards. When these hit the continental shelf in the western Pacific months later, they bounce back eastwards in the form of cold, faster-moving Kelvin waves. These thin the layer of warm water in the eastern Pacific when they arrive several weeks later, helping deeper, colder water reach the surface and bring the El Ni帽o to an end.
鈥淢any different processes are involved in the onset, maturation and demise of El Ni帽o events,鈥� says at the US National Oceanic and Atmospheric Administration.
When will the El Ni帽o end?
The combined forecasts of computer models suggest that this El Ni帽o will be over by June next year, but individual models vary. Some suggest it could persist well into the northern hemisphere鈥檚 summer.
We can鈥檛 predict with any certainty how this event will end, says McPhaden. The 1997 El Ni帽o ended with a bang, with sea-surface temperatures in the eastern equatorial Pacific plummeting by 8掳C in a month, followed by a strong, long-lasting La Ni帽a. But the next strong El Ni帽o in 2015 faded gradually and was followed by a weak, short La Ni帽a.
鈥淪o, at this point, it is difficult to know precisely how the current El Ni帽o will wind down,鈥� says McPhaden. 鈥淣ature loves to confound us with new wrinkles in the epic saga of El Ni帽o, so be prepared for surprises.鈥�
What is certain is that the effects of this event will persist after it ends. Some will be temporary. For instance, the Indian Ocean after El Ni帽os 鈥� on top of the warming due to global heating 鈥� leading to floods in some nearby regions. Some of the worst floods in the Yangtze river occurred in the summer of 1998, after the El Ni帽o that ended in May.
The biggest concern is that the current El Ni帽o could lead to changes that last decades or more. Last year, at Seoul National University in South Korea and his colleagues published a study showing that the combination of extreme El Ni帽os and global warming .
After the 2015 super El Ni帽o, there was a sudden increase in sea-surface temperatures in the Gulf of Mexico that has persisted ever since. The El Ni帽o wasn鈥檛 the only factor involved, says Kug, but it contributed to this jump.
The even-stronger El Ni帽o now under way is more likely to trigger such shifts. 鈥淲e are experiencing a very strong El Ni帽o event,鈥� says Kug. 鈥淏ased on our study, such an extreme event could substantially increase the likelihood that various components of the Earth system are pushed toward, or even across, regime-shift thresholds.鈥�
In other words, in some parts of the world, the climate will never go back to how it was. 鈥淥ur civilisation is adapted to the climate of the 20th century, and it is costly and disruptive to be forced to deal with sudden climate regime shifts,鈥� says Masters.
