Sea temperatures off the western and southern coasts of Ireland are above normal and constitute a marine heatwave, climatologists have said.
UK Met Office data placed the marine heatwave at the “extreme” end of the spectrum, with sea surface temperatures up to 4 degrees above normal.
“Yes, it is a marine heatwave currently,” said Paul Moore, a climatologist at Met Éireann.
“This background warming is always there, but when atmospheric conditions are favourable, as they have been in our region during spring, this can enhance the warming in localised areas, leading to marine heatwaves.”
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Data showing above average temperatures has been confirmed from a number of sources, including figures gathered by Europe’s Copernicus earth-monitoring satellite, and the Irish Marine Data Buoy Observation Network.
This spring was dominated by high-pressure weather conditions, mostly just to the north of Ireland and Britain, said Mr Moore. This has resulted in above average sunshine, he said, and below average winds, generally coming from an easterly direction.
“This has led to the top layer of seas around us warming up at an increased rate, leading to the sea surface temperatures we are seeing now.”
The last time Ireland had comparable sea surface temperatures anomalies was in June 2023.
“This followed a very dry and sunny period during the second half of May and early June that year. Research has linked the marine heatwave then to the record warm June in both Ireland and the UK.”
The reason the west and south coasts had been most affected, said Mr Moore, was because of the mostly easterly winds those areas experienced during May. These easterlies carry warmer air off the land, and this warms the sea faster.
Marine heatwaves have had “devastating consequences” in other parts of the world, said Moore, over the last few years.
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“They can potentially cause widespread bleaching of coral reefs, the proliferation of harmful algal blooms, the displacement of marine species, and the disruption of entire food chains.”
Commenting on the data for Britain and Ireland, Dr Manuela Truebano, from the school of biological and marine sciences at the University of Plymouth, said: “This is unprecedented because it is happening so early in the year.” The June 2023 marine heatwave caused shock at the time. Of added concern, she said, was the “prevalence and intensity of these marine heatwave events”.
Mr Moore said Ireland had been “lucky” with the timing of recent marine heatwaves around its shores because they have occurred before August, which is normally the warmest time of the year for sea surface temperatures here.
If the sea surface temperatures were to continue to be above normal into August, that would put our marine ecosystem under stress, he said.
There are signs that the marine heatwave could end soon, he added.
“The weather pattern is due to change over the next few days, bringing back strong westerly winds, which should churn up the water, mixing colder deep water with the warmer surface water.
“This should ease the sea surface temperature increase, at least temporarily.”
As climate change continues, the global average sea surface temperatures will continue to increase, and this is projected to increase at least up to 2100. – Additional reporting Guardian
