22-05-2025
Wild swimmers rejoice! Sea temperatures around the UK and Ireland soar to 4°C above usual - following an 'extreme' marine heatwave
Wild swimmers have flocked to the seaside as waters around the UK and Ireland are gripped by an 'extreme' marine heatwave.
With temperatures soaring up to 4°C (7.2°F) above usual, British sea temperatures are currently what would be expected for mid-June.
Thanks to an exceptionally warm spring and calm winds, sea temperatures in April and the first half of May were the highest since records began 45 years ago.
Waters have been particularly warm off the west coast of Ireland in a few pockets of Devon and Cornwall.
The entirety of the west coast of the UK is now roughly 2.5°C (4.5°F) warmer than the average for the time of year while water near Scotland is between 2-3°C (3.6-5.4°F) warmer.
A marine heatwave is defined as any period where the sea temperatures exceed the seasonal threshold - 11.3°C for May - for more than five days.
At one point off the Yorkshire coast, near Tyne and Tees, temperatures hit 4.6°C (8.28°F) hotter than average, according to the Centre for Environment, Fisheries and Aquaculture Science.
However, while wild swimmers will definitely enjoy the warmer waters, temperatures are lower than the season peak in late summer and might still feel quite chilly.
The warmest temperatures have been felt off the west coast of Ireland and isolated patched around Cornwall and Devon
Scientists from the Met Office found that the waters around the UK have been coming in and out of a mild heatwave since 2024, but temperatures surged during March as the heatwave spread.
By May 19, temperatures hit an average of 12.69°C (54.84°F) which is well above the heatwave threshold of 11.3°C (52.34°F) for May.
Typically, a marine heatwave only lasts around two weeks.
However, the UK's waters have now been experiencing a heatwave since early March, making it one of the longest heatwaves on record for this time of the year.
Dr Ségolène Berthou, a Met Office climate scientist, wrote in a blog post: 'The heatwave is the result of several overlapping factors.
'Prolonged high-pressure systems brought a dry, sunny spring and weak winds and waves, creating ideal conditions for warming.'
This meant that UK waters started getting warmer in February, a month earlier than in a typical year.
Dr Berthou also points out the sea temperature spike has been particularly sharp due to a layer of warm water forming over the surface.
She says: 'It can be compared to a layer of olive oil floating on water, this thin surface layer allows heat from solar radiation to accumulate near the surface.
'When this layer forms, surface temperatures can increase fast: the last 9 days have seen a sudden additional 1°C warming.'
It isn't yet clear what kind of effects this will have on marine wildlife, but the impact on fish populations is being closely monitored.
A spokesperson for the National Oceanographic Centre told MailOnline: 'The important thing to note is that as the current marine heatwave is occurring before the height of summer, it is unlikely to reach temperatures that would cause major harm or mortality to marine species.'
However, it might disrupt the breeding season of certain species and could lead to a bloom in jellyfish which thrive in warmer waters and change the distribution of some species.
In 2023, after a marine heatwave pushed temperatures 3°C (5.4°F) above average jellyfish sightings rose by 32 per cent.
Professor Tim Smyth, from Plymouth Marine Laboratory, told MailOnline: 'During the current marine heatwave, we are seeing the distribution of where phytoplankton are in the water column more closely resembling summer than spring and this has implications for other parts of the food chain.
'We are also 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 - and on our dinner tables!'
Cooler weather is expected this coming weekend alongside stronger westerly wind which might break up the warm 'olive oil' layer at the surface and allow cooler water to mix in.
That might mean gradually reducing surface temperatures and an end to the heatwave in the coming weeks.
However, scientists warn that climate change is making events like this more likely.
Over the past 40 years, the Met Office has found that the UK's waters are getting 0.3°C warmer on average every decade.
Dr Jonathan Tinker, marine climate scientist at the Met Office, says: 'With projections suggesting UK summer sea temperatures could rise by up to 2.5°C 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.'
SEA LEVELS COULD RISE BY UP TO 4 FEET BY THE YEAR 2300
Global sea levels could rise as much as 1.2 metres (4 feet) by 2300 even if we meet the 2015 Paris climate goals, scientists have warned.
The long-term change will be driven by a thaw of ice from Greenland to Antarctica that is set to re-draw global coastlines.
Sea level rise threatens cities from Shanghai to London, to low-lying swathes of Florida or Bangladesh, and to entire nations such as the Maldives.
It is vital that we curb emissions as soon as possible to avoid an even greater rise, a German-led team of researchers said in a new report.
By 2300, the report projected that sea levels would gain by 0.7-1.2 metres, even if almost 200 nations fully meet goals under the 2015 Paris Agreement.
Targets set by the accords include cutting greenhouse gas emissions to net zero in the second half of this century.
Ocean levels will rise inexorably because heat-trapping industrial gases already emitted will linger in the atmosphere, melting more ice, it said.
In addition, water naturally expands as it warms above four degrees Celsius (39.2°F).
Every five years of delay beyond 2020 in peaking global emissions would mean an extra 8 inches (20 centimetres) of sea level rise by 2300.
'Sea level is often communicated as a really slow process that you can't do much about ... but the next 30 years really matter,' said lead author Dr Matthias Mengel, of the Potsdam Institute for Climate Impact Research, in Potsdam, Germany.
