What’s happening

For more than a year, the surface temperature of the Atlantic Ocean has reached new highs, but in the past few months that trend has reversed at a record pace.

Atlantic temperatures in June were 1–3 degrees Celsius warmer than normal across much of the ocean, with some areas as much as 5 degrees Celsius warmer than average. Such temperatures were not isolated, as record-breaking values ​​have been regularly observed in the Atlantic Ocean since March 2023. That year was the fourth consecutive year that the world’s oceans set new thermal records.

The warmer water was partly a result of anthropogenic climate change, but it was also due to a particularly strong El Niño in 2023 and 2024. But the El Niño period is long over, according to the National Oceanic and Atmospheric Administration.

NOAA data shows that the surface temperature of the Atlantic Ocean has dropped at a surprising rate since May. Since the beginning of June, temperatures have been several degrees colder than normal for this time of year. This means El Niño is likely to be replaced by La Niña — A weather system that allows cold water to rise to the ocean surface.

Both El Niño and La Niña are complex systems that result from a series of causes, the full list of which scientists still do not understand. For this reason, it is very difficult to predict the arrival of each of these warming or cooling periods; our data on them is reduced to actual observations of when the main signs appear and disappear.

La Niña is of no use here

But the current sudden temperature change in the Atlantic is surprising, scientists say No La Niña can explain what they are seeing nowBecause everything is happening extremely fast.

We’ve gone through the list of possible mechanisms and so far nothing looks right.
– said Frans Philippe Tuchen, a graduate student at the University of Miami.

The ocean heatwave has been linked to some devastating ecological consequences, including global coral bleaching, which has stressed more than 99% of tropical reefs in the Atlantic. Bleaching occurs when conditions change and the algae that live on the coral replace it. As a result, corals turn white, which not only affects biodiversity, but also reduces the ability of reefs to moderate coastal storms and reduce flooding.

A recent study found that El Niño could cause trillions of dollars in lost GDP worldwide, an impact that could last for years. It could also lead to increased disease as mosquitoes, toxic algae and bacteria proliferate during long rainy seasons.

We don’t yet know what the consequences of ocean cooling will be because it’s not clear how much the temperature will drop.

The positive side

Cooling of the ocean surface will have positive aspects:

• First of all, if the temperature does not fall below acceptable values, this will balance the previous warming and restore the balance in underwater life. The important thing is that after this cooling, a new warming does not occur, which is of course not guaranteed.
• Second, currents regulate the temperature of the atmosphere; lower water temperatures will mean lower air temperatures in at least some parts of the world.
• Third, colder water is better able to absorb and retain carbon dioxide from the atmosphere, meaning it could increase the ocean’s ability to absorb greenhouse gases and further reduce the rate of global warming.