Expect this fall and winter to be warmer than usual, Pitt environmental science professors advise.
A recurring climate pattern that affects sea surface temperatures, called El Niño, is set to cause higher-than-average temperatures soon. Pitt environmental science professors warn of a strong El Niño this year, in line with a broader pattern of the climate event causing increasingly warm temperatures. While its impact on Pittsburgh is yet to be determined, experts anticipate an atypically warm and dry winter for the region.
Occurring every two to seven years, El Niño occurs when trade winds slow, preventing the Pacific Ocean from its typical cycle of blowing warm water from the Eastern Pacific to the Western Pacific. Because the wind doesn’t push as hard across the ocean during the El Niño phase, warm water accumulates in the eastern Pacific instead of where it usually accumulates on the Western side. This causes sea surface temperatures to rise above normal.
Abigail Carroll, a teaching assistant professor of geology and environmental science, said scientists examine a central area in the tropical Pacific Ocean called the Niño 3.4 rectangle to predict El Niño’s strength by tracking its temperature swings.
During the El Niño phase, the 3.4 area is usually the warmest in the Pacific Ocean and a key indicator of how drastic El Niño’s effects will be for the rest of the world.
“Niño 3.4 has gotten, as of July, the second warmest it has ever been in our El Niño record, which suggests it’s only going to get warmer, and we are set up for a super strong El Niño come this late fall, early winter,” Carroll said.
Carroll said there isn’t enough data to know how climate change could affect future El Niños, with records of El Niños only dating back to the 1950s despite them occurring for thousands of years. However, scientists do know that the El Niño events have been getting warmer with each occurrence.
According to Carroll, El Niño’s opposite weather pattern that causes colder temperatures, called La Niña, have recently caused warmer temperatures than El Niños did 20-30 years ago.
Carroll said climate change has caused oceans to reach the same temperature as the Niño 3.4, which sometimes make El Niño years less powerful. She said that when the difference between ocean temperatures and the Nino 3.4 temperature is more extreme, the impacts of El Niño tend to be more extreme.
Carroll said El Niño has not yet gone into effect, and that recent heatwaves and strong thunderstorms in the Pittsburgh area are more attributable to climate change than El Niño.
According to the National Oceanic and Atmospheric Administration, El Niños tend to push the jet stream that moves storms across the continental U.S. south of its typical position, leading to below-average snowfall in the northern half of the country. Historically, this has meant drier and warmer winters in Pennsylvania.
According to Carroll, it’s hard to tell exactly how El Niño will affect Pittsburgh. She said scientists can only average the probability of events by comparing data sets from past El Niño events. These data sets have tended to follow devastating effects of El Niño such as drought and floods.
“There are trends El Niño tends to follow in terms of cascading events we see in different regions across the world, but sometimes it doesn’t do what we expect,” Carroll said. “So, it’s hard to look at what El Niños have done in Pittsburgh in the past and say it’s definitely going to happen this time and be stronger, but we can put odds on it.”
Mark Abbott, a professor of geology and environmental science, said that El Niño typically causes areas closer to the eastern Pacific Ocean to experience more rainfall than normal, while areas like Australia that are closer to the western Pacific Ocean experience drier weather. These atypical weather patterns can have consequential effects.
“The last [El Niño] caused big forest fires all across Australia,” Abbott said.
Abbott added El Niño can have a large ecological impact by affecting farmers and wildlife. He said warmer ocean waters can shift fish populations to irregular areas, and unpredictable temperatures can stagnate crop output.
“El Niño was really first identified by fishermen who noticed that water temperature changed and the fish were different,” Abbott said. “If you’re a farmer, you want reliable conditions so you can plan your crops, and it doesn’t help if your climate is more extreme.”
Abbott said what we know about the future of El Niño is still uncertain, and that we’re entering a world where there’s no analog, which is measurable and observational data of Earth’s climate system.
“It’s not something that’s easily attainable by sampling,” Abbott said.