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Weather monitoring services in the UK and Ireland have reported a "prolonged" and, in some locations, "extreme" marine heatwave in Northwest European waters, particularly around Ireland and the British Isles.
Marine heatwaves are defined as at least five consecutive days when sea temperatures are in the top 10% of temperatures for that day of the year. According to the UK's Met Office, the current marine heatwave has lasted for over two months, with sea surface temperatures reaching record levels during April and May - the highest for this time of year since satellite monitoring began in 1982.
"This event, now lasting over two months, is significant due to its intensity and persistence. Current sea surface temperatures are warmer by up to 4°C west of Ireland, and by 1.5-2.5°C around the UK coastline: temperatures are what we would usually expect around mid-June," stated Dr Ségolène Berthou in a weather blog posted on the Met Office website.
The temperature anomalies are also being tracked by the Irish meteorological service Met Éireann. In a news update posted on the Met Éireann website, Met Éireann Climatologist Paul Moore said that the elevated sea surface temperatures (SSTs) were in part due to "a persistent area of high pressure to the north of Ireland and the UK throughout spring", which he explained "has brought clear skies, above-average sunshine, and reduced wind speeds. Easterly winds, which are not typical for this time of year, have contributed to rapid warming of surface waters off the west and south coasts by limiting ocean mixing and carrying warmer air from land out to sea."
Researchers at Plymouth Marine Laboratory (PML) are also monitoring the marine heatwave in the English Channel as part of the long-term research project, the Western Channel Observatory.
“The more than centennial dataset from the western English Channel shows that sea-surface temperatures have increased markedly within the past 40 years, at a rate of around 0.6°C per decade. Furthermore, warm anomalies have been increasingly common, and cold anomalies increasingly rare," said Professor Tim Smyth, PML's Head of Science for Marine Biogeochemistry and Observations, in a news update published on the PML website.
"We are seeing increased incidence of species such as tuna and octopus – the latter have been reported to be taking from crab pots, in turn affecting the shellfish industry. Longer term, due to ocean warming, the distribution of species is expected to change, and this will have implications for the species we see in UK waters," Smyth stated.
These findings echo long-term data on climate change released in January by Norway's Institute of Marine Research, showing that the average temperature of Norwegian coastal waters has increased by 1-2ºC since 1935, driving fish species such as cod further north.
According to the US National Oceanographic and Atmospheric Association (NOAA), "Weeks, months, or years of unusually warm waters can cause mass die-offs of fish, marine mammals, and seabirds, disrupt food webs and fisheries, bleach corals, spur harmful algal blooms and wipe out seaweeds. Billions of dollars are lost in such events around the world each year."