Extreme El Niño Events Likely to Increase as World Warms

Photo of swollen river overflowing a dam as it runs under a truss bridge. The river is fast flowing and brown.
The Llano River bursts its banks in Llano, Texas, during historic flooding in fall 2018. The flooding was connected to a strong El Niño that year. New research from The University of Texas at Austin and collaborators says that these extreme El Niño events will become more common as the world warms. Credit: Jonathan Cutrer/Flickr

The most recent ice age peaked around 20,000 years ago and was marked by extensive glaciation and dramatic climate shifts that reshaped Earth’s oceans, landscapes, and ecosystems. A new study involving climate researchers at The University of Texas at Austin Jackson School of Geosciences suggests that this ice age may provide crucial insights into future El Niño weather events. El Niño is one of the most influential climate patterns affecting global weather.

The study, led by the University of Arizona and published in Nature, set out to identify why El Niño weakened during the last ice age when the Earth was colder.

Circular microscope photo filled with many small white shell-like objects.
An 8x-zoomed microscopic image of microfossils dating back to the most recent ice age. Scientists including researchers at the University of Texas Institute for Geophysics studied chemical clues in the microfossil shells to help them build a model of ancient climate. Credit: Kaustubh Thirumalai

The researchers combined an ancient climate record with advanced climate modeling and then ran new simulations on supercomputers at UT’s Texas Advanced Computing Center. They found that the same mechanism responsible for El Niño weakening was supercharging El Niño under global warming conditions.

Jud Partin, a co-author and research associate professor at the Jackson School’s University of Texas Institute for Geophysics (UTIG), said that a major aim of the study was to help decision makers prepare for future extreme weather by improving the reliability of predictions about El Niño’s future.

“We can have more trust in this model for future El Niño because we ran it in the past, it agrees with the data from the past, and the same mechanism explains both the past and future changes,” Partin said.

El Niño is a climate phenomenon characterized by the irregular but periodic warming of sea surface temperatures in the central and eastern Pacific Ocean. This disrupts global weather patterns and can lead to extreme weather events across the world, said lead author Kaustubh Thirumalai, an assistant professor in the University of Arizona Department of Geosciences.

“El Niño is a formidable force of nature – it induces droughts, floods and wildfires, disrupting marine and terrestrial ecosystems across the planet, with pervasive societal impacts across numerous sectors, from agriculture to the aviation industry,” said Thirumalai, who began the research when he was a postdoctoral researcher at UTIG.

Anticipating how El Niño might change in the future is a major priority for climate scientists. But it’s also a major challenge because the world’s leading climate models don’t agree. Some show El Niño intensifying, others show the opposite, Thirumalai said.

To address the uncertainty, the research team – which included collaborators from UTIG, University of Arizona, University of Colorado Boulder, Middlebury College and Woods Hole Oceanographic Institution – turned to the past. They focused on the Last Glacial Maximum — a period about 20,000 years ago when there were ice sheets over much of North America and Europe.

The researchers used a leading climate model to simulate climate conditions from the Last Glacial Maximum through the present day and into the future. The modeling portion of the study was conducted by co-lead author Pedro DiNezo at the University of Colorado Boulder, also a former UTIG climate scientist.

Photo of three men working on a metal pole (the shaft of the coral drill) on a tropical rocky coastline. The sea is in the background.
Jud Partin (center), a climate researcher at the University of Texas Institute for Geophysics and members of a local research team prepare a coral coring drill on Vanuatu in the tropical South Pacific. The corals will help verify findings that El Niño events are strengthening with global warming. Photo: Kaustubh Thirumalai

To test the model, the researchers compared its results with data from the remains of tiny marine organisms called foraminifera. As foraminifera grow, the chemical composition of their shells change based on the water temperature. This preserves a snapshot of ocean conditions at the time the shell formed, which can be compared with model simulations of past climate.

The study found that El Niño intensity varied significantly less during the Last Glacial Maximum compared to the present day, and that future extreme El Niño events became more prevalent as the planet warms.

“The kicker is that El Niño doesn’t just get stronger, those extreme El Niño’s become more frequent,” Partin said.

This could lead to more intense and frequent weather disruptions worldwide. The researchers are making additional tests on the model results using corals recovered from the South Pacific by UTIG researchers, including some that grew 16,000 years ago. The corals will help further confirm the simulations of past El Niño, Partin said. Read more about the UTIG coral research in The Coral Chronicles.

The simulations used in the study were run on TACC’s Lonestar5 and Lonestar6, two of the most powerful academic supercomputers in the US. The climate model, Community Earth System Model, is a collaborative project led by the National Center for Atmospheric Research. The research was funded by the National Science Foundation.

Adapted from a news article published by University of Arizona News.

For more information, contact: Anton Caputo, Jackson School of Geosciences, 512-232-9623; Monica Kortsha, Jackson School of Geosciences, 512-471-2241; Constantino Panagopulos, University of Texas Institute for Geophysics.