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Why is the North Atlantic warming so much?

Why is the North Atlantic warming so much?

Status: 06/19/2023 at 08:12 AM

Water temperatures in the North Atlantic have been very high for about three months now. Is the phenomenon of El Niño behind it? Or missing desert sands? Scientists are baffled about the causes — but they’re very concerned.

The North Atlantic warms up every summer – and it shows. But ocean warming has not been as strong as it is now since satellite measurements began: on June 11, the average value was 22.7 degrees and thus 1.1 degrees above the long-term average for the years 1982 to 2011. Climate Realizer From the University of Maine, collected since 1981.

An exceptional complication

The German Weather Service (DWD) also uses this data. The current record is exceptional in two respects, She says there: “On the one hand, it is the distance to the previous record-holders. On the other hand, it is the unusually long period of almost three months in which the temperature has been higher than in all previous years.”

Physicist Anders Levermann, Head of Complexity Research at the Potsdam Institute for Climate Impact Research, sees it this way: “This is really quite unusual. Even if it is unfortunately an integral part of the long-term warming trend.” The anomaly is also causing great concern internationally.

Desert sand as a reason?

But what is the reason behind the so-called North Atlantic sea surface temperature anomaly? There are different hypotheses about this among scholars. One possible explanation is desert sand, or the lack thereof.

The sand or dust of the North African desert is so fine that winds can carry it thousands of kilometers. “The sand in the air casts a slight shadow on the sea surface, and thus reduces the solar energy that gets there,” Leverman says. But there seems to be less sand in the atmosphere this year. This means that more solar radiation reaches the sea and the sea temperature increases as a result. This thesis is primarily represented by meteorologist and climate researcher Michael Mann of Penn State University.

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or less Sulfur aerosol?

A deficiency of some sulfur aerosols can also play a role. For several years, not much sulfur was allowed to be added to ship fuel. As a result, fewer of these particles — which also have a dulling effect on sea surfaces — enter the atmosphere.

“Aerosols in the air can certainly influence temperature at a regional level. How strong the effect is in this case cannot be said at this time. More investigation is needed,” Leverman says.

Less wind

According to DWD, another possible explanation for the record temperatures is a shift in regions of high and low pressure. Simply put, this creates less wind and therefore less swell. Therefore, warm surface water mixes less with cold water at depth.

Oceanographer Martin Visbeck of the GEOMAR Helmholtz Center for Ocean Research Kiel considers this to be the most important reason. “We are currently seeing a shift in wind zones – also known as the North Atlantic Oscillation. As a result, the trade winds and westerlies, which usually cool the sea surface, are weaker than normal.”

climate change from mainspring

The phenomenon itself is not new. But it’s hitting a much warmer planet — and currently coinciding with El Niño weather. This causes complex changes in the atmospheric circulation and global warming. “We have a long-term trend of global warming. If there are also single events like the current one, we are seeing exceptionally high temperatures very quickly,” explains Vesbeck.

Leverman also agrees: “The most important and widespread change in the climate system that we know about is global warming. Then various other impacts come on top, so to speak.”

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Fish and coral problems

But what are the consequences of record temperatures? For North Atlantic ecosystems, it could have dramatic effects, says Vesbeck. “Corals and certain fish species are likely to experience problems, such as increased coral bleaching. Some fish may have fewer offspring. Some stocks may migrate to cooler polar regions, which in turn can cause problems there.”

The problem is that temperature fluctuations at sea are generally much lower than temperature fluctuations on land. Thus, one degree more than the long-term average is considered an exponential deviation. “Many species are specifically adapted to a particular habitat and temperature. Such drastic changes can have dramatic consequences for them,” Vesbeck says.

Severe storms?

Another consequence that we humans can directly feel. Because warmer oceans mean more water vapor and more energy in the atmosphere – two components of powerful storms. The marine area off the coast of West Africa – where most hurricanes occur – is currently warmer than normal.

Hurricane season has just begun and will continue until the end of November. “Although you can never predict the exact number or strength of hurricanes, the physics is clear: 90 percent of global warming is absorbed by the oceans. This means we give more energy to tropical storms, like hurricanes and hurricanes, and they are getting stronger,” says physicist Leverman. “.

El Niño “ruptures” storms in the Atlantic Ocean

However, the US National Oceanic and Atmospheric Administration (NOAA) calculates a probability of 40 percent for the average hurricane season. The reason for this is El Niño again, as oceanographer Vesbeck explains: “This causes winds at higher altitudes to be faster than those near the surface. But this tends to ‘rip’ the storms, and that’s why they don’t tend to get winded as much. maybe “.

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The consequences could also be felt in Europe. “Because the water temperature off the western and southern coasts of France has just risen five degrees above normal,” says Helge Gosling, a climate physicist at the Alfred Wegener Institute in Bremerhaven. Warmer water temperatures in the North Atlantic can lead to hotter summers in Central Europe through August. Warm air also absorbs more water, which can be carried by westerly and southerly winds to Europe. This encourages heavy rainfall.

This is another reason why current temperature records worry scientists. “As climate researchers, we’ve known for a long time that such events get more violent,” Leverman says. But there is still room to maneuver: “If we can achieve the energy transition in the next 20 years and stop burning coal, oil and gas, we can stabilize the climate and keep more temperature records within limits.”