Aug. 28 (UPI) — When predicting future climate patterns, climate scientists and their models must account for both increasing greenhouse gas emissions and short-term, year-to-year climate oscillations like El Niño and La Niña.
According to a new study, published Friday in the journal Nature Communications, climate scientists can reduce the uncertainty of their models by more precisely simulating subsurface ocean currents in the Pacific.
Most climate models are in broad agreement on how global warming will play out in the coming decades, but even the most precise models inevitably yield a range of potential outcomes.
“The largest differences are seen in the eastern part of the tropical Pacific, a region that is home to sensitive ecosystems such as the Galapagos Islands,” study co-author Malte Stuecker said in a news release.
“How much the eastern tropical Pacific warms in the future will not only affect fish and wildlife locally but also future weather patterns in other parts of the world,” said Stuecker, an assistant professor of oceanography at the University of Hawaii, Mānoa.
The warm and cool phases of the El Niño-Southern Oscillation, El Niño and La Niña, influence weather patterns across the globe.
During an El Niño year, when the Pacific is warmer, trade winds slacken, increasing the risk of flooding in California and weakening the monsoon pattern the people of India and East Asia rely on to flood their rice fields.
When ENSO turns cool, the La Niña pattern sends stronger trade winds across the tropical Pacific. The pattern has implications for ecosystems, fisheries and agriculture throughout the world.
Most climate models yield equally intense El Niño and La Niña phases, but in reality, ENSO’s warming pattern is typically stronger than its cooling pattern.
To better understand this disconnect, researchers analyzed observational data and the simulations of several different climate models.
The analysis showed a link between subsurface ocean current variations and El Niño-La Niña asymmetry. The models with more precisely simulated subsurface ocean currents in the eastern Pacific also yielded more realistic ENSO phases.
“Identifying the models that simulate these processes associated with El Niño and La Niña correctly in the current climate can help us reduce the uncertainty of future climate projections,” said corresponding lead author Michiya Hayashi, research associate at the National Institute for Environmental Studies in Japan.
“Only one-third of all climate models can reproduce the strength of the subsurface current and associated ocean temperature variations realistically,” Hayashi said.
The models featuring more accurate subsurface ocean current simulations predicted that increased El Niño and La Niña intensity is associated with enhanced global warming trends in the Pacific. The same models showed that a decrease in the intensity of the two ENSO phases will precipitate a decline in greenhouse gas-induced warming in the eastern part of the Pacific.
Authors of the new study suggest climate scientists must account for the interplay between wind and ocean in their models in order to more accurately simulate El Niño-La Niña asymmetry.
“The high uncertainty in the intensity change of El Niño and La Niña in response to greenhouse warming is another remaining issue,” Stuecker said.
“A better understanding of Earth’s natural climate swings such as El Niño and La Niña will result in reducing uncertainty in future climate change in the tropics and beyond,” he said.
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