Courtesy of the University of Maine
Usually by this time of year, sea surface temperatures – as a global average – drop dramatically. The southern hemisphere has much more water than the northern hemisphere and it is winter there now. However, the average this year remains abnormally high.
Yes, the oceans have become hotter due to climate change. But something else is going on in the North Atlantic, McNoldy thinks. “What we see in 2023 is so far out of the realm of what has ever happened,” he says. “It’s not just a matter of climate change. Other recent years are not like that. It’s certainly an ingredient – the general trend is up – but it can go up and down from one year to the next. And this year is just so far.”
One possibility has to do with dust from the Sahara — or lack thereof. Typically at this time of year, east-west winds blow across African deserts, filling the atmosphere above the Atlantic with particles. Dust particles act like countless little umbrellas, reflecting some of the solar energy back into space and cooling the ocean. But these winds have been calm recently, clearing the air over the Atlantic and providing more energy to heat the water.
Another has to do with wind: Strong winds blowing across the Atlantic allow it to dissipate some of its heat. It’s the same evaporative cooling you may have felt after swimming in the ocean, says Shang-Ping Xie, a climate scientist at the Scripps Institution of Oceanography who studies the interaction of the atmosphere and the sea: “When the wind blows, you have it cold .” But right now, the winds are weak, trapping heat in the Atlantic instead.”You’re basically suppressing evaporation from the ocean’s surface,” Xie says.
Scientists are also exploring how shipping regulations may have some effect on ocean temperatures. When ships burn fuel with a high sulfur content, they produce aerosols that float in the atmosphere and attract water vapor, brightening clouds. The effect is so dramatic that boats create “ship trails” — white streaks across the ocean that deflect some of the solar energy.