El Niño a key factor, but global warming to increase marine heatwaves
A disruptive ocean heatwave in the northeastern Pacific Ocean in 2014 and 2015 was probably a manifestation of El Niño, says a new study by scientists with the Georgia Institute of Technology and the National Oceanic and Atmospheric Administration (NOAA).
Such warm-water events could become more common as heat-trapping pollution continues to increase in the atmosphere, according to the findings published in the journal Nature Climate Change.
“We had two and a half years of consistent warming, which translated to a record harmful algal bloom in 2015 and prolonged stress on the ecosystem,” said Emanuele Di Lorenzo, a professor in Georgia Tech’s School of Earth and Atmospheric Sciences. “What we do in the study is ask whether this type of activity is going to become more frequent with greenhouse gases rising.”
The study linked the heatwave to weather patterns that started in late 2013. The heatwave caused marine animals to stray far outside of their normal habitats, disrupting ecosystems and leading to massive die-offs of seabirds, whales and sea lions.
The event started in late 2013 when a high pressure area blocked winds the normal winter winds that bring cold Arctic air to the North Pacific. That allowed ocean temperatures to rise a few degrees above average. Later in 2014, the intensifying El Niño spread warmth across the Pacific and by 2015 the region of warm water had expanded to the West Coast, where algal blooms closed fisheries for clams and Dungeness crab.
“The bottom line is that El Niño had a hand in this even though we’re talking about very long-distance influences,” said Nate Mantua, a research scientist at NOAA Fisheries’ Southwest Fisheries Science Center and a coauthor of the study.
“This multi-year event caused extensive impacts on marine life,” Di Lorenzo said. “For example, some salmon populations have life cycles of three years, so the marine heatwave has brought a poor feeding, growth and survival environment in the ocean for multiple generations. Events like this contribute to reducing species diversity.”
“Some of these effects are still ongoing and not fully understood because of the prolonged character of the ocean heatwave,” he said. “Whether these multi-year climate extremes will become more frequent under greenhouse forcing is a key question for scientists, resource managers and society.”