Water temperatures around British Isles have reached up to 4°C above normal, categorised as Category 4 (extreme) marine heatwave
by Victoria Heath
Ocean waters around the British Isles are in the midst of a severe marine heatwave, with temperatures soaring more than 4°C more than usual levels at this time of year. Over the last three months, record temperatures have been seen in the North Atlantic Ocean – with a high of 23°C on 17 June – breaking records set previously in 2010.
The month of May was also the warmest on record since 1850 for the North Atlantic, with temperatures around 1.25°C above average over a reference period of 1961 to 1990, according to the Met Office.
The sea is particularly warm off the coast from Durham to Aberdeen, and off north-west Ireland.
What is causing the British Isles marine heatwave?
Many factors contribute to the British Isles marine heatwave: human-induced climate change has a crucial role, as well as natural causes, according to Professor in Physical Oceanography at Bangor University, Professor Yueng-Djern Lenn.
‘The oceans have already absorbed 90 per cent of the excess heat due to anthropogenic greenhouse gases, and continue to warm. At the same time, we are witnessing an El Niño develop in the tropical Pacific,’ Lenn said. ‘During El Ninos, the global ocean tends to store more heat than usual.
‘There may be other more complicated feedbacks at play as well in driving the UK’s current marine heatwave, but it is too early to say definitively,’ concluded Lenn.
Cleaning up sulphur from marine shipping fuels is most likely adding to the marine heatwave off the British Isles, according to Professor of Climate Physics, Piers Forster of the University of Leeds. There is evidence that there is less Saharan dust over the ocean this year, which normally reflects heat away from the ocean.
Climate scientists are also looking at the significance of other factors, such as the warm phase of the Atlantic Multi-decadal Oscillation since 2020; reduced emissions from shipping; and a persistent easterly winds weather pattern from the continent warming the sea surface.
Effects on marine life
Marine life around the world is being impacted by rising sea temperatures.
‘The immediate effects of these high temperatures are probably biggest in the tropics, where coral bleaching events are known to correlate strongly with warmer temperatures,’ said Professor Rick Stafford, Professor of Marine Biology and Conservation Co-Lead Centre for Ecology, Environment and Sustainability of Bournemouth University.
‘However, warmer seas may also have major implications for temperate seas like the UK. There is evidence that our plankton communities will decrease as temperatures rise, meaning less food for fish, but ultimately less carbon capture and less oxygen production,’ added Stafford.
