Unexplained Cold Patch Appears in Atlantic Ocean in Early 2024
Science/Medical/Technology
Thursday 29th, August 2024
For several months this summer, a significant strip of the Atlantic Ocean along the equator cooled at a record speed, leaving scientists puzzled about what caused the sudden temperature drop. While this cold patch is now gradually warming back to normal, researchers remain uncertain about the underlying causes of the dramatic change.
The cold anomaly, which formed in early June 2024, spans several degrees north and south of the equator. It followed months of unusually warm surface temperatures - the hottest in over 40 years. Although this region of the Atlantic is known to fluctuate between warm and cold phases every few years, the rapid shift from record highs to lows this year was “really unprecedented”, according to Franz Tuchen, a postdoctoral research associate at the University of Miami in Florida, who is closely tracking the event.
“We are still scratching our heads as to what’s actually happening”, said Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration (NOAA), which oversees an array of buoys in the tropics gathering real-time data on the cold patch. “It could be some transient feature that has developed from processes that we don’t quite understand”.
In February and March of 2024, sea surface temperatures in the eastern equatorial Atlantic reached over 30 degrees Celsius - the highest on record since 1982. However, by June 2024, these temperatures began to fall rapidly, reaching their lowest point of 25 degrees Celsius in late July, as noted by Tuchen in a recent blog post.
Forecasts initially suggested that this cooling might develop into an Atlantic Niña - a regional climate pattern that typically brings increased rainfall over western Africa and reduced rainfall in northeastern Brazil and countries along the Gulf of Guinea, such as Ghana, Nigeria, and Cameroon. An Atlantic Niña, although not as powerful as its Pacific counterpart, La Niña, has not occurred since 2013. To be officially classified as an Atlantic Niña, the cooler-than-average temperatures would have needed to persist for three months, until the end of August.
However, with the water warming in recent weeks, “the verdict is already quite certain that it’s not gonna be classified as Atlantic Niña”, said Tuchen.
Understanding the cause of this sudden cooling could help scientists better comprehend the complexities of Earth’s climate and improve weather forecasting. So far, though, none of the anticipated causes have been identified.
Typically, cooler surface waters are associated with stronger trade winds near the equator, which drive Niña events by sweeping away warm surface waters and allowing deeper, cooler water to rise - a process known as equatorial upwelling. Surprisingly, this recent cold patch has coincided with weaker winds southeast of the equator, which “are doing the opposite of what they should be doing if they were the reason for the cooling”, Tuchen explained. “At the moment, we believe that the winds are actually responding to the cooling”.
McPhaden noted that some unusually strong winds developed to the west of the cold patch in May, potentially triggering the rapid cooling. However, those winds “haven’t increased as much as the temperature has dropped”, he said. “There’s something else going on”.
Scientists have modelled various potential climate processes to explain the cooling, including unusually strong heat fluxes in the atmosphere or sudden shifts in ocean and wind currents. “From what we see, these are not obvious drivers of this cooling event”, said Tuchen.
Despite its unprecedented nature, the recent cooling event is unlikely to be linked to human-induced climate change. “I can’t rule it out”, McPhaden acknowledged. “But at first blush, this is just a natural variation of the climate system over the equatorial Atlantic”.
Using data from satellites, oceanic buoys, and other meteorological tools, Tuchen, McPhaden, and other climate scientists are closely monitoring the cold patch and its potential effects on nearby regions - effects which may take months to become evident.
“It’s potentially going to be a consequential event”, McPhaden concluded. “We just have to watch and see what happens”.
While it’s far from the apocalyptic scenario depicted in the film The Day After Tomorrow, where sudden climate changes trigger a new ice age, the mysterious cooling of the Atlantic reminds us of just how much we still have to learn about our planet’s complex climate systems.
The cold anomaly, which formed in early June 2024, spans several degrees north and south of the equator. It followed months of unusually warm surface temperatures - the hottest in over 40 years. Although this region of the Atlantic is known to fluctuate between warm and cold phases every few years, the rapid shift from record highs to lows this year was “really unprecedented”, according to Franz Tuchen, a postdoctoral research associate at the University of Miami in Florida, who is closely tracking the event.
“We are still scratching our heads as to what’s actually happening”, said Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration (NOAA), which oversees an array of buoys in the tropics gathering real-time data on the cold patch. “It could be some transient feature that has developed from processes that we don’t quite understand”.
In February and March of 2024, sea surface temperatures in the eastern equatorial Atlantic reached over 30 degrees Celsius - the highest on record since 1982. However, by June 2024, these temperatures began to fall rapidly, reaching their lowest point of 25 degrees Celsius in late July, as noted by Tuchen in a recent blog post.
Forecasts initially suggested that this cooling might develop into an Atlantic Niña - a regional climate pattern that typically brings increased rainfall over western Africa and reduced rainfall in northeastern Brazil and countries along the Gulf of Guinea, such as Ghana, Nigeria, and Cameroon. An Atlantic Niña, although not as powerful as its Pacific counterpart, La Niña, has not occurred since 2013. To be officially classified as an Atlantic Niña, the cooler-than-average temperatures would have needed to persist for three months, until the end of August.
However, with the water warming in recent weeks, “the verdict is already quite certain that it’s not gonna be classified as Atlantic Niña”, said Tuchen.
Understanding the cause of this sudden cooling could help scientists better comprehend the complexities of Earth’s climate and improve weather forecasting. So far, though, none of the anticipated causes have been identified.
Typically, cooler surface waters are associated with stronger trade winds near the equator, which drive Niña events by sweeping away warm surface waters and allowing deeper, cooler water to rise - a process known as equatorial upwelling. Surprisingly, this recent cold patch has coincided with weaker winds southeast of the equator, which “are doing the opposite of what they should be doing if they were the reason for the cooling”, Tuchen explained. “At the moment, we believe that the winds are actually responding to the cooling”.
McPhaden noted that some unusually strong winds developed to the west of the cold patch in May, potentially triggering the rapid cooling. However, those winds “haven’t increased as much as the temperature has dropped”, he said. “There’s something else going on”.
Scientists have modelled various potential climate processes to explain the cooling, including unusually strong heat fluxes in the atmosphere or sudden shifts in ocean and wind currents. “From what we see, these are not obvious drivers of this cooling event”, said Tuchen.
Despite its unprecedented nature, the recent cooling event is unlikely to be linked to human-induced climate change. “I can’t rule it out”, McPhaden acknowledged. “But at first blush, this is just a natural variation of the climate system over the equatorial Atlantic”.
Using data from satellites, oceanic buoys, and other meteorological tools, Tuchen, McPhaden, and other climate scientists are closely monitoring the cold patch and its potential effects on nearby regions - effects which may take months to become evident.
“It’s potentially going to be a consequential event”, McPhaden concluded. “We just have to watch and see what happens”.
While it’s far from the apocalyptic scenario depicted in the film The Day After Tomorrow, where sudden climate changes trigger a new ice age, the mysterious cooling of the Atlantic reminds us of just how much we still have to learn about our planet’s complex climate systems.
