“What the hell is happening in the North Atlantic?”: The ocean is warming at an alarming rate

The current heat in the world’s oceans worries many scientists – and sometimes leaves them at a loss. For example, Professor Emeritus Eliot Jacobson: “What the hell is happening to the world’s oceans, and the North Atlantic in particular?”, he responds to the current situation in a blog post on his website.

In fact, one temperature record has been chasing the other for months in the North Atlantic. Also in the past 7 days, the surface temperature of the ocean closest to us has averaged 22.7 degrees, about 1 degree above the average of the past thirty years. This is shown by data from the Climate Reanalyzer, a tool developed by climate scientists at the American University of Maine.

It's not just the Atlantic Ocean that records new highs. Global sea temperatures are also alarmingly high. In mid-March, the surface temperature of all oceans averaged above 21 degrees for the first time since satellite recordings began in 1982.

Ocean warming is unusual for two reasons: First, the new temperature records are significantly higher than the old ones. Second, the heat wave has now lasted for more than three months, which is unusually long.

Worrying as the situation is, it doesn't surprise him, says Thomas Frölicher, a climate physicist and professor of ocean modeling at the University of Bern. “Now exactly what us experts have predicted is happening. Namely, that heat waves in the oceans become more frequent, more intense and more widespread as the climate warms.”

For example, in a study published in the journal Science, Frölicher and his team showed that severe heat waves, which kill marine life, have become more than 20 times more common since the start of industrialization. Moreover, the heat waves are getting longer and longer: while the average was still over 30 days in the 1980s, they lasted almost 50 days in the past decade. And the heat waves have been hotter in the recent past.

Even if the recorded temperature anomalies don't seem like much at first glance, if gigantic bodies of water warm up by just a fraction of a degree, huge amounts of extra thermal energy are stored. According to Thomas Frölicher, the global ocean has warmed by an average of 0.1 degrees over the entire water column since 1960. But: "This energy corresponds to that of about 200,000 nuclear power plants like Gösgen in 60 years."

While climate change is undoubtedly responsible for much of the current heat in the world's oceans, it doesn't explain the rapid increase in sea surface in recent months - another concern for scientists.

Some experts say new shipping regulations could benefit the current warm temperatures in the North Atlantic. Because since the beginning of 2020, ships are only allowed to burn fuel with a maximum of 0.5 percent sulphur, previously this was 3.5 percent.

This lowered limit resulted in more than a 75 percent reduction in sulfur oxide emissions, as Eliot Jacobson, Professor Emeritus, writes on his blog: "While this is good for the environment in many ways (e.g. less acid rain and acidification of the ocean), but it also had a not entirely unexpected consequence."

What he means by this: Sulfur particles have a cooling effect because they reflect sunlight back into space. If there are fewer particles, this effect is reduced. This is especially noticeable in the regions of the most important and dense shipping lanes, including the North Atlantic.

However, Thomas Frölicher is not really convinced of the sulfur theory. Because, "This doesn't explain why some parts of the Atlantic Ocean are hotter than others." The explanation with the trade winds seems more plausible to him.

It goes like this: trade winds are constant easterly winds in the equator region all year round. As they blow across the ocean, they cool the sea surface by bringing up deeper and colder water. At the moment, however, the trade winds in the tropical Atlantic and Pacific are weaker - and then they can have the opposite effect. They do this by reducing the mixing of the water layers.

The weak trade winds eliminate another cooling effect: the dust from the Sahara, which is normally carried in large quantities by the winds from the North African desert across the ocean to South America and which reflects the sunlight.

It is remarkable that the temperatures in the ocean are already so high before the onset of the approaching El Niño. El Niño is a weather phenomenon that occurs every two to seven years, alternating with its sister La Niña.

While El Niño is often associated with increased heat, regional dryness and warmer ocean temperatures, La Niña has had the opposite effect, temporarily slowing global temperature increases over the past three years. "We are currently in an intermediate phase," explains ocean expert Frölicher. This means: La Niña has stopped and is no longer cooling, but El Niño has not yet started. When and if El Niño will start is still unclear.

"The authorities in Australia have just announced that there is a 70 percent chance that El Niño will start this year," says the Berner professor. "That would fuel heat on the sea surface for weeks and months to come." This can have serious consequences for marine ecosystems: fading corals, dying seagrass and kelp forests are just a few examples.

And that's not all: as Frölicher and his colleagues were only recently able to demonstrate, heat waves often occur in conjunction with other extreme events such as oxygen deprivation and acidification. "Such combined extremes put a much heavier burden on ecosystems." He assumes that such a combined event is currently taking place in the subtropical Atlantic Ocean.