Sea surface temperatures in the Atlantic have been hitting record highs for over a year, but that trend has reversed at record speed over the past few months, and no one is sure why.
In June, ocean temperatures in the Atlantic Ocean were 2 to 5 degrees Fahrenheit (1 to 3 degrees Celsius) warmer than normal in most areas, and as much as 9 degrees Fahrenheit (5 degrees Celsius) warmer than normal in some areas. These temperatures were not a one-off: the Atlantic has been regularly hitting record-breaking levels since March 2023. That year marked the fourth consecutive year that the world’s oceans set new heat records.
The warming ocean temperatures are partly due to human-induced climate change, but also due to a particularly strong El Niño event in 2023 and 2024. But that event appears to have passed, according to the National Oceanic and Atmospheric Administration.
According to NOAA data, sea surface temperatures in the Atlantic Ocean have been dropping at an alarming rate since May. Since the start of June, temperatures have been 1-2 degrees Fahrenheit colder than normal for this time of year. This means that El Niño will likely be replaced by La Niña, a weather system that brings cooler water to the surface of the Atlantic Ocean, sometime between September and November. Both El Niño and La Niña are complex systems driven by trade winds, solar heating, and tropical rainfall, and can be difficult to predict. Still, the sudden change in temperature in the Atlantic is puzzling, and no one seems to know why it happened so quickly.
“We’ve looked through a list of possible mechanisms and so far none fit the bill,” Frans-Philippe Tuchen, a postdoctoral researcher at the University of Miami, told New Scientist.
Marine heatwaves have been associated with several devastating environmental impacts, including the global coral bleaching event that stressed over 99% of tropical coral reefs in the Atlantic Ocean. Bleaching occurs when environmental changes expel the algae that live on corals, causing them to turn bone-white, not only impacting biodiversity but also reducing the ability of reefs to buffer the effects of coastal storms and reduce flooding.
El Niño and La Niña have global impacts that go far beyond changes in water temperature. Recent studies have shown that El Niño can cause trillions of dollars in GDP losses worldwide, with effects that could last for years. They also increase disease incidence, as longer rainy seasons encourage the proliferation of mosquitoes, toxic algae and bacteria.
