The sea off the coast of the UK and Ireland is experiencing an unprecedented marine heatwave with temperatures increasing by as much as 4C above average for the spring in some areas.
Marine biologists say the intensity and unprecedented nature of the rise in water temperatures off the coasts of Devon, Cornwall and the west coast of Ireland are very concerning. As human-induced climate breakdown continues to raise global temperatures, the frequency of marine heatwaves is increasing.
“This is unprecedented because it is happening so early in the year,” said Dr Manuela Truebano, from the school of biological and marine sciences at the University of Plymouth. “To see these temperature rises around UK waters at this time of year is quite sobering. Each time it happens we use the word ‘unprecedented’, and I am very concerned at the increase in prevalence and intensity of these marine heatwave events.”
Temperatures in the sea off the south coast of Devon, Cornwall and Ireland have risen by between 2C and 4C above average temperatures for this time of year.
Dr Dan Smale, of the Marine Biological Association, said the usual springtime water temperatures would be 11C-12C, but the waters were now at absolute temperatures of 15C-16C.
The UK is increasingly being hit by marine heatwaves, with sea temperatures in June 2023 reaching their highest levels since records began. At the time the warming was labelled as “unheard of”.
Truebano said the rise in sea temperatures so early in the spring was even more concerning. The marine heatwave began in March and has continued for almost two months. If the sea temperatures continue to rise into the summer months there are fears of mass die-offs of fish and other marine life.
Marine biologists say the impacts of the spring marine heatwave could be profound, including changes in the reproductive patterns of plankton, which in turn could lead to reductions in fish numbers later in the year.
Smale said: “It is a concern that these warming events are happening more and more in the UK and Ireland. Traditionally UK waters have not been affected, but these events are starting to happen more frequently and the associated temperatures are increasing.
“If this continues through the summer we would expect to see widespread biological impacts. This is a significant warming event.”
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The Met Office said the marine heatwave had lasted more than two months, from early March and continuing into May. “It is significant due to its intensity and persistence,” it said.
It said the increase in heat was the result of several overlapping factors including prolonged high-pressure systems which brought a dry, sunny spring and weak winds and waves, creating ideal conditions for warming.
The sea began to warm from mid February – one month earlier than usual – and rose in temperature from a warmer baseline as the waters around the UK were already warmer than usual coming out of winter.
Data shows marine heatwaves are increasing in frequency. A 2019 study found the number of heatwave days rose by more than 50% in the 30 years to 2016, compared with the period from 1925-54. Scientists said at the time the heat destroyed swaths of sea life “like wildfires take out huge areas of forest”.
Dr Jonathan Tinker, a marine climate scientist at the Met Office, said: “With projections suggesting UK summer sea temperatures could rise by up to 2.5C by 2050, such events are likely to become more frequent, intense and longer-lasting. Marine heatwaves offer a glimpse into how changing ocean conditions could shape future weather conditions.”
