What is Causing the North Atlantic to Smash Heat Records?

Over the past few weeks, sea-surface temperatures in certain parts of the North Atlantic Ocean have risen to record levels. The warming is occurring in a broad section that extends nearly one-third of the way across the Atlantic from the northwestern coast of Africa to the west. According to Brian McNoldy, a meteorologist at the University of Miami in Coral Gables, Fla., satellite data reveals that some surface waters in the area are nearly 4 degrees Celsius (about 7 degrees Fahrenheit) higher than average for this time of year. “There’s been record-breaking warmth since March, but even more so now,” he notes.

On June 10, for example, the average sea-surface temperature for a portion of the Atlantic that stretches from the equator to 60 degrees north, up to southern Norway, southern Greenland, and central areas of Canada’s Hudson Bay was around 22.7° C (almost 73° F). This is about 1 degree C higher than average from 1991 to 2020, McNoldy highlights. The previous record for the same date, 22.1° C, occurred in 2010.

“This year’s warmer-than-normal waters might help strengthen storms that form in the eastern Atlantic and eventually spawn hurricanes,” scientists say.

The reason for the unusual warm-up is unclear, but several factors may be at play. Sometimes, vast stretches of desert dust from the Sahara float across the ocean, carried by winds stirred up by a semi-permanent high-pressure system called the “Azores high” due to its proximity to those islands. However, lately, the Azores high has weakened and shifted southwest away from Africa. As a result, the winds that typically transport Saharan dust westward over the North Atlantic are quieter and mostly dust free, according to Michael Mann, a climate scientist at the University of Pennsylvania. 

As a result, the dark waters are heated by solar radiation that would be usually scattered back into space by the dust. If and when the trade winds strengthen, increased dust from Africa could help mitigate the situation to some extent.

In 2020, new emissions regulations took effect for long-haul container ships. There has been some speculation that less pollution could lead to more warming. With fewer plumes scattering sunlight back into space, more radiation penetrates the sea surface. But some studies suggest that the cooling effect of ship plumes may have been negligible. Not only do the exhaust plumes have a short life span, but the pollutants can also cause natural clouds to evaporate more quickly and thus lead to warming rather than cooling. 

This year marks the return of El Niño, a climate phenomenon characterized by warmer-than-normal sea-surface temperatures along the equator west of South America. According to scientists with the National Oceanic and Atmospheric Administration’s Climate Prediction Center, by winter, there’s more than an 80% chance that the El Niño will either be strong or moderate. In general, El Niño boosts average surface temperatures worldwide, both on land and at sea, says Mann. Human-caused climate change has done the same.

However, there is still a lot of uncertainty about how the current conditions may impact the upcoming forecast. The warmer waters in the North Atlantic may tend to intensify storm systems that later develop into tropical depressions and hurricanes. However, the developing El Niño in the equatorial Pacific may hamper their formation by strengthening winds in the upper atmosphere that can shear the tops off nascent hurricanes. Scientists say how active this year’s hurricane season will be depends on which of these forces will prevail.

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