Climate change driven by greenhouse gas emissions may lead to more frequent extreme El Niño events, according to recent research.
As El Niño’s effects are felt from mid-2023 to mid-2024, global temperatures have set record highs for 12 consecutive months. Being one of the most powerful El Niño events recorded, it has likely contributed to severe heat, flooding, and droughts across the globe.
A study released on September 25 in the journal Nature by a climate scientist from the University of Colorado Boulder and collaborators indicates that if greenhouse gas emissions continue to rise, the world may experience more frequent extreme El Niño events by 2050.
“It’s quite alarming that 2050 is not far off,” stated Pedro DiNezio, co-lead author of the paper and associate professor in the Department of Atmospheric and Oceanic Sciences. “If these extreme occurrences happen more often, society might struggle to recover, rebuild, and adapt before the next El Niño arrives. The fallout could be catastrophic.”
Changing Winds and Rising Temperatures
El Niño develops when the water temperatures along the equator in the Pacific Ocean rise by at least 0.9 °F above the average for a prolonged period.
Although this temperature increase appears slight, it can alter wind patterns and ocean currents, leading to extreme weather around the world, such as heat waves, flooding, and droughts.
When the temperature in this region rises by 3.6°F above average, it’s classified as an extreme El Niño event. Since the National Oceanic and Atmospheric Administration has been tracking this data since the 1950s, it has noted no more than four extreme El Niño events.
Extreme El Niño events tend to have severe consequences for global weather. For instance, during the winter of 1997-98, this event resulted in record rainfall in California, causing landslides that tragically claimed over a dozen lives. During the same time, roughly 15% of the world’s coral reefs were lost due to extended warming.
Last winter, DiNezio noted, El Niño almost reached extreme levels.
“El Niño events are tricky to model and forecast because they are influenced by many factors. This complexity has made it challenging to create accurate predictions that would assist society in preparing and mitigating potential damages,” they added.
Earlier studies suggest that climate change is worsening and increasing the frequency of extreme weather occurrences, potentially tied to shifts in the El Niño patterns. Still, scientists have yet to definitively confirm if El Niño will strengthen with rising temperatures due to a lack of sufficient data.
In their research, DiNezio and colleagues used a computer model to simulate El Niño events over the past 21,000 years, beginning from the peak of the last Ice Age.
The model indicates that during the Ice Age, characterized by colder global temperatures, extreme El Niño events were very uncommon. However, as the planet has warmed since the Ice Age ended, both the frequency and intensity of El Niño have been on the rise.
To verify the model, the team compared the simulated results with historical ocean temperature data obtained from fossilized shells of foraminifera—tiny one-celled organisms that existed in the ocean long before humans. By analyzing the oxygen isotopes preserved in these shells, they reconstructed how El Niño influenced ocean temperature changes across the Pacific over the last 21,000 years. The ancient data matched well with the model’s outputs.
“We are the first to demonstrate a model that can accurately simulate past El Niño events, boosting our confidence in its projections for the future. Though we are pleased with the methodology we’ve developed for our validation process, it unfortunately reveals distressing news,” DiNezio remarked.
The model forecasts that if greenhouse gas emissions continue unabated, half of all El Niño events could be extreme by 2050.
The Controlling Factor
Despite El Niño’s intricate nature, the model indicates that a single factor has governed the frequency and intensity of all El Niño events as global temperatures have increased since the last Ice Age.
When water in the eastern Pacific Ocean warms due to natural variations, the trade winds that typically blow from east to west over the equatorial region weaken because of changes in atmospheric pressure above the ocean. During an El Niño, this weakening allows warm water to shift eastward, further diminishing the winds and creating a feedback loop known as the Bjerknes feedback.
DiNezio’s research suggests that as atmospheric temperatures rise rapidly from greenhouse gas emissions, the planet will experience an intensified Bjerknes feedback, resulting in more frequent extreme El Niño events.
With the latest El Niño now past, DiNezio stressed the importance of society taking steps to mitigate the effects of future extreme events, including reducing emissions and supporting communities, especially in developing countries, to enhance their resilience against extreme weather.
“We now have a better grasp of how these extreme events occur, and the key is to lessen our dependence on fossil fuels,” they stated. “Our results underscore the urgent necessity of limiting global warming to 1.5 °C to prevent disastrous climate impacts.”
