Ice age clues and advanced climate models reveal how El Niño weather patterns change

The last ice age peaked about 20,000 years ago, with massive glaciations and dramatic climate changes that transformed Earth’s oceans, landscapes and ecosystems. According to a study led by the University of Arizona, Earth’s last ice age could provide important insights into future El Niño events, one of the climate patterns that most influences Earth’s weather.

The study, published in the journal Nature, combines data from ancient shells of marine organisms with advanced climate models to reveal how El Niño patterns may change in a warming world.

El Niño is a climatic phenomenon that causes irregular and cyclical increases in sea surface temperatures in the central and eastern Pacific Ocean, disrupting global weather patterns and causing extreme weather events such as droughts, floods and heat waves.

“El Niño is a formidable force of nature – it causes droughts, floods and wildfires, devastates marine and terrestrial ecosystems around the world and has far-reaching societal impacts across many sectors, from agriculture to aviation,” said Kausuthabu Thirumalai, co-lead author of the study and assistant professor in the University of Alberta’s School of Geosciences.

El Niño events occur approximately every two to seven years, and predicting how these phenomena will change in the future is a major challenge for climate scientists.

“There are several cutting-edge climate models that suggest different responses of El Niño to current and future anthropogenic warming,” Tirumalai said. “Some say El Niño variability will increase, others say it will decrease. It’s a complex, multifaceted phenomenon, so figuring out what’s going to happen to El Niño is an important priority for climate science.”

To address this uncertainty, the research team (which included collaborators from the University of Alberta, University of Colorado Boulder, University of Texas, Middlebury College, and Woods Hole Oceanographic Institution) looked to the past. They focused on the Last Glacial Maximum, a period about 20,000 years ago when ice sheets covered much of North America and Europe.

The researchers simulated climate conditions from the Last Glacial Maximum to the present using the Community Earth System Model, a collaborative project led primarily by the National Center for Atmospheric Research and involving numerous institutions. The modeling portion of the study was conducted by co-senior author Pedro Dinezo of the University of Colorado Boulder.

To test their model, Tirumalai and his team compared their results with data on the remains of tiny marine organisms called foraminifera, which are found in marine samples taken from the seafloor containing layers of sediment that have been deposited over thousands to millions of years.

“These beautiful microscopic organisms float in the upper ocean and build shells that trap ocean temperature while they’re alive,” Tirumalai said.

As foraminifera grow, they extract material from the surrounding seawater to form their shells. The chemical composition of these shells changes with water temperature, preserving a snapshot of ocean conditions at the time the shells formed.

When foraminifera die after a few weeks, their shells sink to the ocean floor and become part of the sediment. By analysing shells from different layers of sediment, scientists can reconstruct ocean temperatures thousands of years ago and compare them to model simulations of past climates.

By analysing individual foraminifera shells, the team was able to capture seasonal temperature changes that would be otherwise undetectable.

“We will zoom in on a small section of the sediment core and analyse multiple shells from the same layer, which will give us a range of temperatures in the Pacific over a short period of time and allow us to compare them to the ice age and now,” Tirumalai said.

The study found that El Niño variability during the Last Glacial Maximum was significantly lower than it is today, and that extreme El Niño events may become more frequent in the future as the planet warms, which could lead to more intense and frequent weather disruptions around the world.

Importantly, these findings suggest a common mechanism for extreme El Niño variability during both glacial periods and future conditions, allowing researchers to test climate model predictions.

“This gives us more confidence in the models’ predictions for the future,” Tirumalai said. “If we can accurately simulate past climate change, we have a better chance of getting reliable predictions for future changes in El Niño.”