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The world could see more multi-year El Nino and La Nina events due to human activities, according to a new study published in Nature journal.
El Nino and La Nina are the warm phase and cool phases of a recurring climate pattern across the tropical Pacific Ocean called the El Nino-Southern Oscillation (ENSO). In 2023, La Nina ended its three-year run and El Nino announced its arrival.
The climate patterns typically last nine to 12 months. In ENSO, the atmosphere and ocean influence each other.
In the new study, researchers found that Walker Circulation, the atmospheric component of ENSO driving weather patterns across the world, has changed its behaviour since the industrial era.
“We set out to determine whether greenhouse gases had affected the Pacific Walker Circulation,” lead author Georgy Falster, a research fellow at the Australian National University and the ARC Centre of Excellence for Climate Extremes, said in a statement.
The overall strength of the Walker circulation has not changed yet. But they are seeing changes in year-to-year behaviour, Falster explained.
The researcher and her colleagues wanted to reconstruct how the Walker circulation has shown variations across 800 years from 1200 through 2000. They collected data from ice cores, trees, lakes, corals and caves.
“They aren’t thermometers, but they contain information about the climate,” Samantha Stevenson, an associate professor at the University of California Santa Barbara’s Bren School of Environmental Science & Management and the co-author of the study, explained in a statement.
The ice core, trees, lakes, corals and caves accumulate heavier or lighter versions of oxygen and hydrogen depending on the weather conditions. The researchers calculated the ratios of these elements in the samples and reconstructed Walker circulation patterns over 800 years.
The time it takes for the Walker circulation to go from El Nino to La Nino has slightly slowed, indicating that multi-year climate patterns are likely to increase, the researchers observed.
“That means in the future we could see more of these multi-year La Nina or El Nino events as the atmospheric flow above the Pacific Ocean switches more slowly between the two phases,” Falster said. These changes could increase the risks of drought, fire, rain and floods.
Though the strength of Walker circulation has not decreased, researchers speculate that with high carbon dioxide levels, there is a chance for the Walker circulation to weaken. Also, most climate models show that the Walker circulation could decrease by the turn of the century.
There is more. The researchers also noted that the Walker circulation weakens in the aftermath of volcanic eruptions.
“Following a volcanic eruption, we see a very consistent weakening of the Pacific Walker circulation,” Bronwen Konecky, an assistant professor at Washington University in St Louis, said in a statement.
This causes El Nino-like conditions following eruptions. Weaker Walker circulation indicates El Nino and stronger circulation signals La Nina.
El Nino events, they found, followed three volcanic eruptions in the twentieth century. These include Mount Agung in 1963, El Chichón in 1982 and Mount Pinatubo in 1991.
“Understanding how the Pacific Walker circulation is affected by climate change will enable communities across the Pacific and beyond to better prepare for the challenges they may face in the coming decades,” Sloan Coats, study co-author from the University of Hawaii, said in a statement.