A recent study published on Sep. 25 in 'Nature' by a University of Colorado Boulder climate scientist and collaborators reveals that if greenhouse gas emissions continue unchecked, extreme El Nino events could become much more common by 2050.
"It's pretty scary that 2050 is not very far away," said Pedro DiNezio, co-lead author of the study and associate professor in the Department of Atmospheric and Oceanic Sciences. "If these extreme events become more frequent, society may not have enough time to recover, rebuild and adapt before the next El Nino strikes. The consequences would be devastating."
El Nino's Impact on Global Weather
El Nino occurs when water temperatures along the equator in the Pacific Ocean rise at least 0.9 F above average for an extended time. This seemingly small increase can cause shifts in wind patterns and ocean currents, which trigger unusual weather events such as heat waves, floods, and droughts across the globe.
An extreme El Nino is classified when temperatures rise by 3.6 F above average. The U.S. National Oceanic and Atmospheric Administration has recorded four extreme El Nino events since the 1950s. During these extreme occurrences, global weather impacts are more severe. For example, during the 1997-98 El Nino, California experienced record rainfall that caused landslides, and 15% of the world's coral reefs were lost due to prolonged ocean warming.
In the most recent El Nino event, which nearly reached extreme magnitude, DiNezio explained, "El Nino 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," they said.
Simulating the Future of El Nino Events
DiNezio and his team used computer models to simulate El Nino events over the last 21,000 years, starting from the peak of Earth's last Ice Age. Their research shows that as the planet warmed after the Ice Age, both the frequency and intensity of El Nino events increased.
The research team validated their models by comparing simulated data with actual ocean temperature data derived from the fossilized shells of foraminifera, a type of single-celled organism found in the ocean. By analyzing oxygen compounds preserved in these ancient shells, they were able to reconstruct El Nino-related temperature shifts across the Pacific Ocean, which aligned with the simulations.
"We are the first to show a model that can realistically simulate past El Nino events, enhancing our confidence in its future predictions. We are also proud of the robust technique we developed to evaluate our model, but unfortunately, it brought us no good news," said DiNezio.
Their model predicts that if greenhouse gas emissions continue at the current rate, one in two El Nino events could become extreme by 2050.
The Role of Atmospheric Feedback Loops
The research team identified that the Bjerknes feedback, a process in which weakened winds and warmer water reinforce each other during El Nino, has played a key role in controlling the frequency and intensity of El Nino events since the last Ice Age. As the planet warms due to greenhouse gas emissions, this feedback loop becomes stronger, leading to more frequent and intense El Nino events.
DiNezio stressed the importance of reducing greenhouse gas emissions to mitigate future extreme El Nino events and help vulnerable communities adapt to extreme weather conditions. "We now understand how these extreme events happen, and we just need the will to reduce our reliance on fossil fuels," they said. "Our findings emphasize the urgent need to limit warming to 1.5 C to avoid catastrophic climate impacts."
Research Report:Future increase in extreme El Nino supported by past glacial changes
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