Record-breaking sea temperatures have been recorded off the west coast of Ireland and in pockets along the coasts of Cornwall and Devon, with potential implications for marine life and people planning to go swimming.
UK Sea Temperatures Soar After Exceptionally Warm Spring
The seas around the UK and Ireland have experienced a significant surge in temperature over the past week, with some areas reaching 4C warmer than normal. This heatwave has potential implications for marine life and people planning to go swimming.
Sea temperatures vary greatly depending on location, depth, and time of year.
The warmest sea temperatures are found in the tropics, where they can reach up to 30°C (86°F).
In contrast, polar regions have freezing cold temperatures, often below 0°C (32°F).
Global average sea temperature is around 17°C (63°F), with seasonal fluctuations of 5-10°C (9-18°F) in temperate and subtropical zones.
Understanding these variations is crucial for marine life, climate modeling, and human activities like fishing and tourism.
Heatwaves Off the West Coast
The intensity of this heatwave is most pronounced off the west coast of Ireland, as well as pockets along the coasts of Cornwall and Devon. Scientists at the National Oceanography Centre and the Met Office attribute this phenomenon to climate change, which is causing oceans worldwide to warm up.
Climate change refers to significant long-term changes in the Earth's climate.
These changes can be caused by natural factors, such as volcanic eruptions, or human activities, like burning fossil fuels and deforestation.
Human-induced climate change is primarily driven by greenhouse gas emissions from industrial processes, transportation, and agriculture.
Rising temperatures are causing melting of polar ice caps, sea-level rise, and extreme weather events.
According to Dr. Ségolène Berthou at the Met Office, ‘It’s super intense at the moment. The marine heatwave has really soared this week.‘ This surge in sea temperatures is the highest recorded for April and the first half of May since monitoring began 45 years ago.
Marine Heatwaves and Climate Change
Climate change is making marine heatwaves like this one more likely, as oceans warm around the globe. Scientists expect 2025 to be one of the hottest years on record for air temperatures. A marine heatwave is defined as sea temperatures exceeding the seasonal threshold for more than five consecutive days.
The Impact on Marine Life
The west coast of the UK is now about 2.5C above average, with Scottish waters being 2-3C warmer than usual. Dr. Berthou notes that ‘it started in the North Sea and the Celtic Sea. Now the North Sea has cooled down a bit but the west of Ireland is extremely hot.‘ This surge in temperature could have significant impacts on marine life.
While the temperatures have not yet exceeded the upper limit that marine life can tolerate, Dr. Zoe Jacobs warns that this heatwave may disrupt species’ breeding patterns and bring an influx of jellyfish to seas and beaches. Jellyfish blooms can occur when waters are warmer, causing harmful algae to grow out of control and potentially poisoning other life.
Previous Heatwaves and Impacts
Previous heatwaves have caused mass mortality among mussels in 2018 and increased jellyfish sightings by 32% in 2023 following a marine heatwave with temperatures 3-4C above average. The heat could also encourage different fish to move into UK waters, potentially increasing the amount of fish to catch.
The Ocean’s Response
Marine heatwaves can push up land temperatures too, as sea breezes carry the heat off the ocean. This happened in May 2024 when a short marine heatwave contributed significantly to above-average land temperatures. In some parts of the world, such as Australia and the Pacific, marine heatwaves can destroy coral reefs or local fisheries.
The UK’s Vulnerability
While the UK is generally more protected from these impacts due to its cooler waters, scientists still have much to discover about marine heatwaves and their effects on marine life. A recent study by Dr. Jacobs found that the southern North Sea and the English Channel are hotspots for such events, where heatwaves can last longer than in other areas of the country.
A Look Ahead
The long spell of warm, dry weather is expected to break slightly this weekend, but it might be just a temporary dip as the longer-range forecast suggests the weather will warm up again. Oceans have absorbed 90% of the excess heat created by human activities and have warmed overall by 1C over the past few decades.
The sea surface temperatures in the North Atlantic have been increasing by around 0.3C per decade over the last 40 years, according to the Met Office.
Sea surface temperature (SST) is the average temperature of the uppermost layer of the ocean.
It plays a crucial role in Earth's climate system, influencing weather patterns and marine ecosystems.
SST varies depending on factors such as latitude, season, and ocean currents.
In tropical regions, SST can reach up to 28°C (82°F), while in polar regions it can drop below -1.8°C (28.8°F).
Changes in SST are closely linked to global warming, with rising temperatures affecting marine life and ecosystems.
