Marine heat wave near UK, Europe

Sea temperatures at 170-year high

The ocean waters surrounding the United Kingdom and much of Europe are baking in an unprecedented marine heat wave, which scientists say is being intensified by human-caused climate change. Scientists are astounded not only by how much the waters have warmed during the past month, but also by how early in the year the heat wave is occurring. The exceptionally warm waters are a threat to marine life and could worsen heat waves over land this summer, they say.

Sea surface temperatures are running as high as 9 degrees Fahrenheit above normal, the warmest in more than 170 years, and are more typical of August and September when the waters are usually at their warmest. The event has registered as a Category 4 on the National Oceanic and Atmospheric Administration’s marine heat wave scale with localized areas reaching Category 5, the two highest categories on the scale.

NOAA defines a marine heat wave as a period of persistent and unusually warm ocean temperatures, “which can have significant impacts on marine life as well as coastal communities and economies.” The agency describes Category 4 as “extreme” and Category 5 as “beyond extreme.”

Last month was the warmest May since 1850 for the North Atlantic around the United Kingdom and the warmest compared to the average for any month, the country’s Met Office reported. And that was before water temperatures soared in early June, in part because of abundant sunshine and warm breezes from the southwest, said Met Office meteorologist Aidan McGivern in a video update Tuesday.

The average sea surface temperature near the United Kingdom and Ireland is closing in on 59 degrees Fahrenheit, which has only happened once before in June, tweeted Ben Noll, a meteorologist at the National Institute of Water and Atmospheric Research in New Zealand. “It seems very likely that June 2023 will set a new record in the region as sea temperatures continue to rise,” Noll said.

The North Atlantic heat wave is part of a rapid warming of global ocean waters since March that has scientists confused about the cause and concerned about its impacts.

Global ocean surface temperature reached a record high in May for the second consecutive month, NOAA said in a report last week, and it appears to have continued at a record pace during June. The chance of seeing such warm sea surface temperatures is 1-in-256,000 according to Brian McNoldy, a hurricane researcher at the University of Miami.

NOAA forecasters say the marine heat wave conditions in the North Atlantic have a 90 to 100 percent chance to continue through August and a 70 to 80 percent chance to last through the end of the year, although the intensity of the heat is predicted to decrease. Most of the world’s oceans have at least a 70 percent chance of marine heat wave conditions persisting at least through the summer, NOAA predicts.

The unusually warm waters in the tropical Atlantic are already influencing the hurricane season, having helped Tropical Storm Bret form the farthest east of any storm on record so early in the season. Longer-term impacts of warming oceans could include higher sea levels, more intense storms with heavier rain, and more frequent regional marine heat waves like the one surrounding Europe now.