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Surface temperature in the Atlantic at record high: How the various factors interact is not clear
Photo: Nora Carol Photography / Getty Images
Already in March of this year, a record value was reached. The surface water of the North Atlantic has never been as warm as it has been for the time of year. The current temperature is 23.1 degrees Celsius – a good 1.1 degrees warmer for mid-June than the average of the past 40 years. Another temperature record, this time in the water: Scientists are not surprised. Nevertheless, many are worried. This is because the significant deviation in temperatures, the size of the affected area and the timing are unusual – and they cannot yet be conclusively explained.
One thing is certain: There is most likely no such thing as a single trigger. Presumably, there are various factors that may have favored the rise in temperature. One of them is climate change. This is because humans continue to release vast amounts of greenhouse gases into the atmosphere and thus continue to heat up the earth, and consequently also the world's oceans. Much of the heat is absorbed here. "The ongoing warming of the ocean is as worrying as it is expected with advancing climate change," said Johanna Baehr, head of climate modeling at Universität Hamburg's Center for Earth System Research and Sustainability. Till Kuhlbrodt, a research associate in the Oceanography Group at the University of Reading, says: "I think the simultaneous occurrence of extreme warming in different ocean regions is worrying."
In addition to the human factor, there are natural climate fluctuations – this year, for example, El Niño. Currents that drive up the global average temperature, while its counterpart, La Niña, has a cooling effect. Every few years they occur alternately. In both cases, ocean and air currents in and over the equatorial Pacific are changing, but the effects are global. For example, El Niño leads to heavy rainfall and flooding in some regions of South America, and drought and drought in Australia. Due to man-made climate change, these naturally induced extremes are often even more severe.
"The fact that this coincides is a coincidence"
However, oceanographer Mojib Latif from the GEOMAR Helmholtz Centre for Ocean Research Kiel does not see the phenomenon as a cause for the current temperatures. "El Niño has nothing to do with what's happening in the Atlantic," he told SPIEGEL, "the fact that it coincides is a coincidence." And because everything coincides with rising temperatures in times of global warming, records are being set again and again, as is the case now. On the other hand, he considers it unlikely that warming in the Pacific could have triggered a temperature peak in the North Atlantic at the beginning of the El Niño phase.
According to the climate researcher, there are two wind systems that have caused temperatures to rise. Winds have a cooling effect through evaporation – if they weaken, so does this effect. According to Latif, this applies on the one hand to the northeast trade winds that blow from the east side of the Atlantic towards South America, and finally further west into the Caribbean. If the trade winds are weaker and thus also the currents in the water, the corresponding marine regions become warmer. This has been the case since April and temperatures have climbed, "we have had the highest measured values since temperatures have been recorded".
In recent weeks, the so-called westerly winds, which distribute cold air from North America over the Atlantic and also reduce evaporation, have also weakened further. How the marine regions have warmed – the subtropical region since spring and more northern parts of the ocean for a few weeks now – would speak in favour of the explanation of the winds, Latif said.
But there are other theories as to what may have led to the North Atlantic temperature high. Stefan Rahmstorf, head of the Earth System Analysis Research Department at the Potsdam Institute for Climate Impact Research, calls it "more speculative".
Desert dust from the Sahara can lay like a protective shield across the Atlantic. Winds blow the small dust particles over the water, where they have a cooling effect. They reflect the light of the sun, so less heat reaches the water. How many of these dust particles disperse over the sea depends on the winds that transport them there. But because the easterly winds are relatively weak, the cooling effect also increases. "This may have a small share in the warming," says oceanographer Latif, assessing the theory. "But this would be more limited to the eastern Atlantic."
Another hypothesis is that warming is seen as a consequence of environmental protection: ships on the Atlantic now sail more often with fuels that release less sulfur when burned. Sulphurous exhaust gases, however, have a cooling effect similar to that of Saharan dust. However, the rise in temperature and the decrease in emissions do not go together: while the water became warmer and warmer almost by leaps and bounds, the exhaust gases were reduced over a long period of time.
Some of the consequences of the warm water are already becoming apparent. Several fish, for example, washed up dead on the coast off Texas. Too little oxygen in the water, that's the reasoning of the Quintana Beach County Park. Swimming in the region is not recommended, the bacterial load is probably high. The warmer the water in the oceans, the harder it is for fish, corals and other marine animals. Even if the current temperature peak flattens out again, it probably won't be the last. "I'm particularly worried about the long-term changes," says Latif, "not the current situation."
Research will first have to show which factors actually favor the increasing surface temperatures and how large their respective share is. "Regardless of the cause of the respective regional ocean warming, these will influence the respective weather in the neighboring countries," says Baehr. It is almost impossible to make a reliable prediction. However, temperature fluctuations in the ocean could favor the occurrence of heat waves, droughts and heavy precipitation depending on the region.
This will also be felt in Europe. Throughout the summer, temperatures could be above average. Because it is not only El Niño that is causing temperatures to rise, but now also the North Atlantic.