23-05-2025
Why Ireland is experiencing a 'marine heatwave' right now
The warm spell of weather over the country the past number of weeks is set to break over the coming days. But climatologists say it has precipitated a ' marine heatwave ' with sea temperatures off the western and southern coasts of Ireland rising above normal. UK Met Office data placed the marine heatwave at the extreme end of the spectrum, with sea surface temperatures up to 4 degrees above average confirmed by the Irish Marine Data Buoy Observation Network. Paul Moore, climatologist with Met Éireann, joined RTÉ Radio 1's Morning Ireland to explain. (This piece includes excerpts from the conversation which have been edited for length and clarity - you can hear the discussion in full above).
What is a marine heatwave and what does it do?
A marine heatwave is when the sea surface temperatures are significantly above average for a long period of time. "So that means, at this particular time of year, the May average might be 12 degrees, and we're 4 degrees or 3 degrees above that at the moment," he says. "We're not in the warmest part of the year for sea surface temperatures, that's usually in August, so if they continue to rise as they normally do, that's when we can hit problems if if they're way above average in August."
What problems do marine heatwaves cause?
"In the past, marine heatwaves around the world, when they come at the peak of the sea surface temperatures it can it can cause devastation to the marine life. Because the marine life wouldn't be used to that, so the ecosystem would come under a lot of stress. So far we've been lucky, two years ago we got a marine heatwave in June, but then it kind of eased as the weather changed and more westerlies came in, and now we've got a marine heat wave in May, and it looks like it might ease over the next few weeks as the weather changes," says Moore. "But if we had these weather situations in August, that would push the already highest seasonal temperatures of the year higher than normal, and that's when we could see problems with our marine ecosystem."
Does the colder weather bring temperatures back down?
"Yes, that's what we saw in June 2023 when the weather broke in mid-June and towards the end of June, the colder waters from beneath mixed up and we got back to more normal [temperatures]. But normal is still above average now: all our sea surface temperatures have been rising gradually due to climate change anyway, so this is on top of that. So when we get an event like this, that's what it brings: the extremes on top of what the climate change is doing already."
