A red line. That’s what scientists around the world have been doing all week. The red line, which shows the development of the temperature of the North Atlantic Ocean, received a lot of attention from this weekend because it shows an unprecedented increase in temperature: the water in the Atlantic Ocean has never been so warm before.
When the line started to climb gently in March and broke the first records, the alarm bells were already ringing, but many scientists still thought that the warming was mainly due to the arrival of El Niño. This natural climate phenomenon, which occurs every two to seven years, releases extra heat into the air, causing temporary global warming, separate from man-made warming caused by greenhouse gases. But after the announcement by the US Oceanography and Meteorology Agency (NOAA) last week that El Niño is really happening, all eyes were on the rapidly rising red line.
Elevated y-axis
The numbers don’t lie: the sea water of the Atlantic Ocean currently has a temperature of almost 23 degrees Celsius. That is more than a degree above the average of the forty years in which comparable data has been kept. Eliot Jacobson, a mathematician who created the NOAA data graph, wrote on Twitter that he had to “raise the upper limit of the y-axis” to represent the water temperature deviation.
The extreme temperatures do not only apply to the Atlantic Ocean: the average sea surface temperature in all oceans, with the exception of the polar regions, is 0.2 degrees Celsius higher than last year, and almost a degree above the average from 1982 to 2011. Everyone is agree that an exceptional situation has arisen, but opinions differ on the cause of this deviation.
Read also: Scientists predict new El Niño and temporary additional warming
Intense discussions
Scientists have been having heated discussions for a week, in which various theories are put forward. The main explanation is the aforementioned El Niño, which brings additional heat from the Pacific Ocean, causing the average temperature around the world to rise slightly. The World Meteorological Organization warned last month that the chance of the earth warming 1.5 degrees Celsius in 2027 due to this phenomenon is two in three. But that alone is not enough to explain the temperature records.
Some scientists also emphasize another effect of El Niño. Due to the weather phenomenon, the trade winds blowing from West Africa to North America were unprecedentedly weak this spring, resulting in less Saharan sand being released into the air over the Atlantic Ocean. These grains of sand block sunlight and bounce it back up without the sun’s rays reaching the surface. In this case, cleaner air also means more heat, which may explain (part of) the high sea surface temperature in the Atlantic Ocean.
Blackout sulfur particles
Other scientists argue that the sulphate content in marine fuels plays a role. In 2020, the International Maritime Organization reduced the maximum amount of sulfur in fuels from 3.5 to 0.5 percent, with the aim of combating air pollution in coastal areas. But temperature rise is a possible unexpected consequence. Indeed, sulfur particles can reflect sunlight off the earth, “darkening the surface,” writes mathematician Jacobson.
Now that much less sulfur particles are being emitted, it is possible that more sun rays reach the water and warm some coastal areas as a result. But whether that really has a major impact on the water temperature is not clear. According to Michael Mann, a climate researcher at the University of Pennsylvania, the effect of sulfate is minimal: the only scientific study on the subject has shown that there is only a small connection, he writes on Twitter. The lack of sulfate particles can raise the water temperature by a maximum of 0.05 degrees Celsius – only a fraction of the increase that is happening now.
Less oxygen for ecosystems and tropical storms
Finally, a few also link the temperature rise to the eruption of the submarine Hunga Tonga volcano in the South Pacific in January 2022. The explosion released large amounts of water vapor into the atmosphere, where the vapor is still still hangs. This also retains heat, heating the earth’s surface (including the sea water).
Whichever theory ultimately turns out to be correct, the scientists agree on one thing: the long-standing trend of warming due to greenhouse gas emissions has made extreme situations such as the one in the Atlantic Ocean much more likely. And the possible consequences, from less oxygen for ecosystems to tropical storms, are alarming.