As with many natural phenomena, scientists look to past climate to understand what might happen next as the Earth warms. By evaluating the so-called “flavors” of El Niño events in past climate records and model simulations, the researchers get a clearer picture of El Niño patterns over the past 12,000 years and can more accurately reflect future changes and effects of this powerful force. The study, by scientists at the University of Hawai’i at Manoa and the University of Colorado Boulder, was published recently. Nature Communication.
“We used a unique set of climate model simulations spanning the Holocene over the last 12,000 years and accounted for changes in the frequency of El Niño flavors during different El Niño events, the three preferred locations where warming peaks occur — at the UH Manoa School of Ocean and Earth Sciences and Technology. (SOEST) lead author of the study and associate professor of atmospheric sciences Christina Karamperidou, “Eastern Pacific, Central Pacific and coastal. “Doing so has allowed us to reconcile conflicting records of past El Niño behavior.”
El Niño is the primary factor influencing variability in water temperature and trade winds in the Pacific. Typically, researchers look for indicators of El Niño events in ancient, preserved materials such as coral skeletons, Peruvian mollusk shells, or lake sediment from the tropical Andes because they are locked into past indicators of temperature and precipitation across the Pacific.
“However, depending on where the samples were taken — eastern Pacific, Central Pacific or near the coast of South America — the frequency of El Niño events seems to show different patterns,” Karamperidou said. “Records from the eastern Pacific show an intensification of El Niño activity from the early Holocene to the late Holocene, while records from the central Pacific show highly variable El Niño throughout the Holocene.”
The new set of climate model simulations developed by Karamperidou and co-author Pedro DiNezio, associate professor at the University of Colorado Boulder, are the first to allow exploration of changes in the frequency of El Niño flavors over the past 12,000 years. This enabled the researchers to test a hypothesis that Karamperidou and colleagues put forward in 2015 – that paleoclimate records in the Pacific could be explained by changes in El Niño flavors.
“In fact, we have shown that the Eastern Pacific events increased in frequency from the early Holocene to the late, whereas the Central Pacific and Coastal events decreased in frequency, leading to changes in the hydroclimate in the tropical Pacific,” Karamperidou said. “Importantly, we have shown that not only their frequency but also the strength of their effects vary, which is important for interpreting past climate records.”
The surprising effect of El Niño on the coast
Additionally, this is the first study of the response of coastal El Niño events to climate change. During these events, conditions in the rest of the Pacific basin are normal or colder-than-normal, while sea surface warming is limited off the coast of South America.
“These coastal events have enormous impacts, with severe flooding and disasters in countries like Peru and Ecuador,” Karamperidou said. “In fact, in another recent paper we showed that while these events don’t feel like the more widely known East and Central Pacific events around the world, a better understanding of the mechanisms driving them is essential to understanding the drivers of the other two flavors.”
Links to Hawaii’s rainfall, its dangers
El Niño events have significant effects on Hawai’i’s precipitation, trade wind strength, hurricane probability, and drought, and the type of El Niño event is important for these effects.
“This information is important, among others, for water resource managers to better prepare for Hawaii’s regional climate,” Karamperidou said. “Therefore, it is imperative that we better understand the mechanisms of these flavors and also improve their representation in climate models and evaluate their predicted changes in future climatic conditions.”
This study provides new insights into how El Niño may respond to climate change, and thus can help reduce these uncertainties in global climate models and therefore estimates of El Niño effects.
materials provided by University of Hawaii at Manoa. Originally written by Marcie Grabowski. Note: Content can be edited for style and length.