Assessing El Niño ‘flavors’ to tease out past variability, future impact

As with many natural phenomena, scientists look at past climate to understand what may happen as Earth warms. By evaluating the so-called “flavors” of El Niño events in past climate records and model simulations, the researchers have a clearer picture of El Niño patterns over the past 12,000 years and can more accurately project changes and future impacts of this powerful force. The study, conducted by scientists at the University of Hawai’i at Manoa and the University of Colorado Boulder, was recently published in nature communications.

“We used a unique set of climate model simulations spanning the Holocene, the last 12,000 years, and accounted for changes in the frequency of El Niño flavors, the three favorite places where peak warming occurs during different El Niño events Eastern Pacific, central Pacific and coastal,” said Christina Karamperidou, lead author of the study and an associate professor of atmospheric sciences in Manoa UH’s School of Ocean and Earth Sciences and Technology (SOEST). “Doing this allowed us to reconcile conflicting records of past El Niño behavior.”

El Niño is the main factor affecting the variability in water temperature and the strength of the trade winds in the Pacific. Typically, researchers look for indicators of El Niño events in ancient and preserved material, such as coral skeletons, Peruvian mollusk shells, or lake sediments from the tropical Andes because they contain indicators of past temperature and rainfall in the Pacific.

“However, depending on where the samples are taken (eastern Pacific, central Pacific, or off the coast of South America), the frequency of El Niño events appears to exhibit different patterns,” Karamperidou said. “Records from the eastern Pacific show an intensification of El Niño activity from the early to late Holocene, while records from the central Pacific show a large variation of El Niño throughout the Holocene.”

The new set of climate model simulations developed by Karamperidou and co-author Pedro DiNezio, an associate professor at the University of Colorado Boulder, are the first to allow the study of changes in the frequency of El Niño flavors over the past 12,000 years. . This allowed the researchers to test a hypothesis that Karamperidou and his colleagues put forward in 2015: that paleoclimate records in the Pacific could be explained by changes in El Niño flavors.

“Indeed, we show that eastern Pacific events have increased in frequency from the early to late Holocene, while central and coastal Pacific events have decreased in frequency, resulting in hydroclimate changes in the tropical Pacific.” Karamperidou said. “Importantly, we show that it is not just their frequency, but also the strength of their impact that changes, which is important for interpreting past climate records.”

Surprising impact of coastal El Niño

Furthermore, this is the first study on the response of coastal El Niño events to climate change. During these events, sea surface warming is limited to the coast of South America, while conditions in the rest of the Pacific basin are normal or colder than normal.

“These coastal events have large impacts with severe flooding and disasters in countries like Peru and Ecuador,” Karamperidou said. “In fact, we showed in another recent paper that although these events are not globally felt as the best-known eastern and central Pacific events, a better understanding of the mechanisms driving them is essential to understanding the drivers of the other .two flavors, too.”

Hawaiian Rainfall Connections and Hazards

El Niño events have significant impacts on Hawaii’s precipitation, trade wind strength, the likelihood of hurricanes and drought, and the type of El Niño event is important to these impacts.

“This information is important for water resource managers, among others, to better prepare for Hawaii’s regional climate,” Karamperidou said. “Therefore, it is imperative that we gain a better understanding of the mechanisms of these flavors, and also improve their representation in climate models and assess their projected changes in future climate conditions.”

This work offers new insights into how El Niño may respond to climate change and thus may help to reduce these uncertainties in global climate models and thus in predictions of El Niño impacts.

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Materials provided by University of Hawaii at Manoa. Originally Posted by Marcie Grabowski. Note: Content can be edited for style and length.

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