Global warming to drive more extreme weather through multi-year La Ninas, climate scientists say
Extreme weather events such as wildfires and floods could become regular occurrences as global warming shifts established weather patterns, according to research by scientists in China, the United States and Australia.
In a paper published in the journal Nature on July 26, the climate researchers said they expected global warming to increase the frequency of multi-year La Nina events, suggesting that weather extremes like those that have occurred since 2020 will occur more frequently.The El Nino-Southern Oscillation (ENSO) is a natural weather phenomenon involving fluctuating ocean temperatures in the central and eastern equatorial Pacific, as well as changes in atmospheric pressure, according to the World Meteorological Organization.HSBC, Keppel to explore climate mitigation cooperation in Greater Bay Area
During warm El Nino events, the sea-surface temperature increases, while during cold La Nina events, the temperature falls. La Nina can affect patterns of monsoons and tropical cyclones, as well as increase occurrences of flooding and wildfires.
In their study, the team of international scientists used the latest climate models from the Coupled Model Intercomparison Project Phase 6 to project changes to La Nina over a 100-year period.El Nino events typically peak within a year and cause large heat discharges in the upper-ocean of the equatorial Pacific. The La Nina events that tend to follow initiate a regenerative process, but as the recharge is typically weaker than the discharge, the events can last for two years or longer, according to the paper.
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Future changes to multi-year La Nina events in response to global warming largely remained unknown, the researchers said in their paper.
However, the team said they did advance their understanding of multi-year La Nina events, in particular, a “two-way interaction between the tropics and subtropics that intensifies under greenhouse warming”.
The paper revealed more about the one-way influence on El Nino by subtropical winds and variations in sea-surface temperatures – collectively known as the North Pacific Meridional Mode.
The research team said they found that, under both low and high-emission greenhouse warming scenarios, easterly wind irregularities in the subtropical North Pacific broadened in the northern direction in response to warm irregularities in the equatorial eastern Pacific.
A slower heat recharge of the equatorial Pacific due to the northward broadening easterly winds caused the La Nina events to stretch into a second year, the researchers said.
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According to the Chinese Academy of Sciences (CAS), as global warming takes hold, the tropical-subtropical interaction becomes more efficient because of faster warming patterns in the Pacific, which means that El Nino events will generally be more efficient at generating multi-year La Nina events.By combining all selected models, the team found that in a high greenhouse gas emissions scenario, the frequency of multi-year La Nina events this century will increase by about a third compared to the previous century.
The paper called for cuts to greenhouse gas emissions to “alleviate the adverse impacts of increased multi-year La Nina”, according to study co-author Jia Fan, from the CAS Institute of Oceanology.Climate change made July hotter for 4 out of 5 people on Earth: scientists
Geng Tao, a researcher at the Ocean University of China, and first author of the paper, said that the effect of a strong El Nino during a winter activating a La Nina in the following winter was a North Pacific Meridional Mode-like response.
Last year, China experienced unusually high amounts of rainfall and extreme weather due to an ongoing La Nina event, with average May to mid-June rainfall in the southern provinces of Guangdong, Guangxi and Fujian reaching 621 millimetres (24 inches) – the most since 1961, according to state media CGTN.“These findings suggest that the weather extremes seen during the 2020-2022 La Nina will probably occur more frequently in the near future,” Geng said in a CAS statement.
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