There have been dramatic changes to marine life as a result of seas around the UK having their warmest start to the year since records began, according to provisional data from the UK Met Office.
Ireland’s seawater temperatures, however, have declined since a marine heatwave occurred during exceptionally warm weather in May, but continue above normal in the east and south, Met Éireann climatologist Paul Moore said.
UK Met Office data placed May’s heatwave at the extreme end of the spectrum, with the Irish Marine Data Buoy Observation Network confirming sea surface temperatures were up to 4 degrees above average.
The average surface temperature of UK waters in the seven months to the end of July was more than 0.2 degrees higher than in any year since 1980, with dramatic changes in marine life evident due to this prolonged heating, analysis of the provisional Met Office data by the BBC concludes.
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Scientists and citizen naturalists have observed a remarkable range of species not usually widespread in UK waters, including octopus, bluefin tuna and mauve stinger jellyfish.
The abundance of these creatures can be affected by natural cycles and fishing practices, but many researchers point to the warming seas as a crucial part of their increased presence.
“Things like jellyfish, like octopus ... they are the sorts of things that you expect to respond quickly to climate change,” Dr Bryce Stewart, a senior research fellow at the Marine Biological Association in Plymouth, told the BBC.
“It’s a bit like the canary in the coal mine – the sorts of quite extraordinary changes we’ve seen over the last few years really do indicate an ecosystem under flux."
Atlantic bluefin tuna have been seen along Britain’s southwest coast in large numbers this year and have been increasingly detected in Irish waters. Bluefin tuna numbers have been building over the past decade for a number of reasons, including warmer waters and better management of their populations.
But extreme heat, combined with historical overfishing, is pushing some cold-adapted species like cod and wolffish to their limits.
“We’re definitely seeing this shift of cooler water species moving north in general,” Dr Stewart added.
The seas around Ireland and the UK are now considerably warmer than even a few decades ago, a trend driven by the burning of fossil fuels.
Warmer seas intensify hurricanes and storms, while there are particular changes to Atlantic currents due to warming that could alter normal weather patterns profoundly.
The world’s oceans have taken up about 90 per cent of the Earth’s excess heat from humanity’s emissions of planet-warming gases, including carbon dioxide.
This spring was dominated by high-pressure weather conditions, mostly just to the north of Ireland and Britain, resulting in above-average sunshine and below-average winds, generally coming from an easterly direction.
A marine heatwave is when the sea surface temperatures are significantly above average for a long period of time. The warmest part of the year for sea surface temperatures is usually in August, with the latest data confirming waters off the south and west of England are exceptionally warm. Further south, the Bay of Biscay is experiencing temperatures 1 to 2 degrees above normal.
Ireland still has above-average temperatures along the south and east, with waters off the north and west coasts nearer the average, Mr Moore said.
Water temperatures in the Irish Sea were 15.3 degrees on Monday, close to the average for August. In Co Cork, waters were at 16.8 degrees, above the average of 16.2 degrees.
This may change over the coming week, Mr Moore added, as Ireland is forecast to have winds predominantly from a southerly direction “which is like to exacerbate sea temperatures”.
Mr Moore confirmed the overall trend of warming in the Atlantic, with temperatures “well above the 1991-2020 long-term average”. A marine heatwave in the Mediterranean intensified a “heat dome” over France and Spain in recent weeks.
The Met Office says its data from the end of June 2024 to now is provisional and will be finalised in the coming months, but this usually results in only very minor changes.
