With the climate pattern known as El Ni帽o in full force from mid-2023 to mid-2024, global temperatures听. As one of the strongest El Ni帽o events on record, it was likely the main culprit of unprecedented heat, floods and droughts worldwide.
In a published Sep. 25 in the journal Nature, a CU Boulder climate scientist and collaborators reveal that the planet could see more frequent extreme El Ni帽o events by 2050 if greenhouse gas emissions continue to increase.听
鈥淚t鈥檚 pretty scary that 2050 is not very far away,鈥� said Pedro DiNezio, the paper鈥檚 co-lead author and associate professor in the Department of Atmospheric and Oceanic Sciences. 鈥淚f these extreme events become more frequent, society may not have enough time to recover, rebuild and adapt before the next El Ni帽o strikes. The consequences would be devastating.鈥澨�
Pedro DiNezio
Shifting wind and soaring temperatures
El Ni帽o occurs when water temperatures along the equator in the Pacific Ocean rise by at least 0.9 掳F above average for an extended period.听
The seemingly marginal temperature change can shift wind patterns and ocean currents, triggering unusual weather worldwide, including heat waves, floods and droughts.听
When the area , scientists classify the El Ni帽o event as extreme. Since the U.S. National Oceanic and Atmospheric Administration began collecting data in the 1950s, the agency has recorded three to four extreme El Ni帽o events.听
During an extreme El Ni帽o, the impacts on global weather tend to be more severe. For example, during the winter of 1997-98, 听El Ni帽o brought , causing devastating landslides that killed more than a dozen people. Over the same period, the planet due to prolonged warming. 听听
Last winter El Ni帽o almost reached extreme magnitude, DiNezio said.听
鈥淓l Ni帽o events are difficult to simulate and predict because there are many mechanisms driving them. This has hindered our ability to produce accurate predictions and help society prepare and reduce the potential damage,鈥� they said.
Prior research suggests that climate change is intensifying and increasing the frequency of extreme weather events, possibly linked to changes in El Ni帽o patterns. However, due to limited data, scientists have yet to confirm whether El Ni帽o will strengthen with warming.
Satellite sea surface temperature departure in the Pacific Ocean for听October 2015, where darker orange-red colors are above normal temperatures and are indicative of El Ni帽o.听(Credit: NOAA)
DiNezio and their team set out to simulate El Ni帽o events in the past 21,000 years鈥攕ince the peak of Earth鈥檚 last Ice Age鈥攗sing a computer model.
The model shows that during the Ice Age, when Earth鈥檚 climate was colder, extreme El Ni帽o events were very rare. As the planet warmed since the end of the Ice Age, the frequency and intensity of El Ni帽o have been increasing.听
The team validated the model by comparing the simulated data with past ocean temperature data retrieved from fossilized shells of foraminifera, a group of single-celled organisms ubiquitous in the oceans long before human existence. By analyzing the type of oxygen compounds preserved in these fossilized shells, the team reconstructed how El Ni帽o drove ocean temperature fluctuations across the Pacific Ocean for the past 21,000 years. The ancient record aligned with the model鈥檚 simulations.听
鈥淲e are the first to show a model that can realistically simulate past El Ni帽o events, enhancing our confidence in its future predictions. 听We are also proud of the robust technique we developed to evaluate our model, but unfortunately, it brought us no good news,鈥� DiNezio added.听
The model predicts that if society continues to pump greenhouse gases into the atmosphere at the current rate, one in two El Ni帽o events could be extreme by 2050.听
The control knob
Despite El Ni帽o鈥檚 complexity, the model reveals that a single mechanism has controlled the frequency and intensity of all El Ni帽o events as the planet warmed since the last Ice Age.
When the eastern Pacific Ocean water warms from natural fluctuation, the winds that always blow east to west over the equatorial Pacific weaken due to changes in air pressure above the ocean. But during an El Ni帽o, weakened winds allow warm water to flow east, and the warmer water weakens the winds even more, creating a feedback loop known as the Bjerknes feedback.
DiNezio鈥檚 research suggests that as the atmosphere warms rapidly from greenhouse gas emissions, the planet experiences a stronger Bjerknes feedback, leading to more frequent extreme El Ni帽o events.
With the most recent El Ni帽o now in the past, DiNezio emphasized that society needs to focus on taking measures to reduce the impact of future extreme El Ni帽o events, including cutting emissions and helping communities, particularly those in the developing countries, become resilient to extreme weather.听
鈥淲e now understand how these extreme events happen, and we just need the will to reduce our reliance on fossil fuels,鈥� they said. 鈥淥ur findings emphasize the urgent need to limit warming to 1.5 掳C to avoid catastrophic climate impacts.鈥澨�
