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Makes makes El Niño so unpredictable?

A new study from the Institute for Basic Science has identified the key mechanisms that cause El Niño events to be inconsistent. The international team of climate scientists found that the complexity and unpredictability of El Niño and La Niña events can be traced back to two atmosphere-ocean oscillations with different characteristics and frequencies.

Study lead author Axel Timmermann is the director of the IBS Center for Climate Physics (ICCP) at Pusan National University.

“Our study reveals that there is a hidden structure in the seemingly chaotic and unpredictable occurrence of El Niño events,” said Timmermann.

El Niño events are characterized by an unusual period of warming in the central to eastern Equatorial Pacific that can last up to a year. Many of these events transition to a La Niña, or a cold state, which usually has a duration of one to two years.

El Niño events often result in a dry spell across Southeast Asia and the western tropical Pacific, while boosting rainfall near the coastline of the eastern Pacific in countries such as Ecuador and Peru.

El Niño’s remote “ripple effects” do not only have an impact on the atmosphere, but also influence ocean currents, ecosystems, extreme weather events, global markets, and national economies.

El Niño events are not predictable – some are relatively weak, while others are strong. In addition, they may occur in the central Pacific or emerge farther east. These differences determine which areas will be hit the hardest by climate extremes and which ones will be spared. The accurate prediction of an El Niño event requires an understanding of the diversity behind this  system.

Last year, a team of 40 climate scientists from 11 countries analyzed massive amounts of climate observations and computer model simulations to investigate what underlies El Niño diversity.

The research team found that El Niño events in the eastern Pacific are characterized by a return time of 3-7 years, while events in the central Pacific tend to return every 2-3 years.

The different characteristics that emerge with these events are determined by how strongly the atmosphere and the ocean interact with each other. These interactions are an important source for El Niño irregularity, and limit how far in advance some of these events can be predicted.

Study co-author Fei-Fei Jin is a professor of Atmospheric Sciences at the University of Hawaii.

“Finally we can attribute the observed complexity of the most powerful natural climate engine to the co-existence of two oscillatory states of the underlying mathematical equations,” said Professor Jin.

Co-lead author Professor Jeongseong Kug added: “More comprehensive climate modeling studies have to be conducted now to test our new ideas in a more realistic setting and to determine whether we can expect shifts in El Nino characteristics in our warming world.”

The study is published in the journal Nature.

By Chrissy Sexton, Staff Writer

Image Credit: NASA Earth Observatory

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