Large parts of the Atlantic near the equator are cooling at record speed – and scientists cannot figure out why
This summer, a wide swath of the Atlantic Ocean along the equator cooled at a record rate for several months. Although the cold zone is now warming back to normal temperatures, scientists are still baffled as to what caused the dramatic cooling in the first place.
The anomalous cold patch, which is limited to a stretch of ocean several degrees north and south of the equator, formed in early June after a months-long period of the warmest surface waters in more than 40 years. Although this region is known to fluctuate between cold and warm periods every few years, the speed with which it fell from a record high to a low this time is “truly unprecedented.” Franz Tuchena postdoctoral fellow at the University of Miami in Florida who is following the event, told Live Science.
“We are still puzzling over what is actually happening here,” Michael McPhadena senior scientist at the National Oceanic and Atmospheric Administration (NOAA), who monitors a series of buoys in the tropics that collect real-time data from the cold zone, told Live Science. “It could be a transient phenomenon that has evolved from processes we don’t yet fully understand.”
Sea surface temperatures in the eastern equatorial Atlantic were hottest in February and March, when they exceeded 30 degrees Celsius—the warmest months since 1982. As June arrived, temperatures mysteriously began to drop, reaching their coolest at 25 degrees Celsius in late July, Tuchen wrote in a recent Blog post.
According to forecasts, the cooling event could develop into an Atlantic Niña phenomenon, a regional climate pattern that tends to increase rainfall over West Africa and decrease it in northeastern Brazil and the countries bordering the Gulf of Guinea, including Ghana, Nigeria and Cameroon. The phenomenon, which is not as strong as the La Niña phenomenon, Counterpart in the Pacificand has not occurred since 2013, would have been declared if the below-average temperatures had persisted for three months, until the end of August.
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However, the cold pocket of water has warmed up in recent weeks, so “the verdict is already pretty certain that it will not be classified as an Atlantic Niña,” Tuchen said.
However, if we can find out exactly what caused the dramatic cooling, scientists could better understand the peculiarities of the Earth. climatewhich could ultimately benefit weather forecasting, said Tuchen. But none of the expected processes are yet to materialize.
“There’s still something going on”
Cooler surface waters are typically accompanied by stronger trade winds that flow near the equator and are the most influential drivers of Niñas, as they sweep away warm surface waters and cause deeper, cooler water to rise through a process known as equatorial upwelling. Puzzlingly, the most recent cold region coincides with weaker Winds southeast of the equator that are “doing the opposite of what they should be doing if they were the cause of the cooling,” Tuchen said. “Right now, we believe the winds are actually responding to the cooling.”
McPhaden noted that some unusually strong winds that developed west of the cold zone in May may have triggered the cooling at a record pace, but those winds “have not increased as much as the temperature has decreased,” McPhaden said. “There’s something else going on.”
Scientists have modeled a handful of possible climate processes to explain the observed cold zone, such as enormous heat flows in the atmosphere or sudden changes in ocean and wind currents. “As far as we can see, these are not obvious causes for this cooling event,” Tuchen said.
Although the recent dramatic cooling is unprecedented, it is unlikely to be caused by human-induced climate change. “I can’t rule it out,” McPhaden said. “But at first glance, this is just a natural change in the climate system over the equatorial Atlantic.”
Tuchen and McPhaden are among several climate scientists who are using data from satellites, ocean buoys and other meteorological instruments to closely monitor the cold snap and its future impacts on surrounding continents – which will not become apparent for months.
“This could be a momentous event,” McPhaden said. “We’ll just have to wait and see what happens.”
