Climate change added up to 2 °C to European sea temperatures, study finds

Attribution of record water temperatures

An international team of researchers from Switzerland, Sweden, the United States, Ireland, and the United Kingdom published an analysis through World Weather Attribution on 19 August 2026 assessing the role of greenhouse gas emissions in warming European waters. Analyzing the hottest 14-day periods in July and across the entire year, the scientists determined that recent peak sea surface temperatures across four European coastal zones would have been virtually impossible in a pre-industrial climate. Human-induced warming has added approximately 2 °C to the Mediterranean Sea, 1.4 °C to the Bay of Biscay and the Iberian coast, and 1.3 °C to the Celtic Sea. Average surface temperatures across the Mediterranean reached 27 °C in July, setting a monthly record, while an offshore buoy near Dragonera off Mallorca recorded 33 °C on 6 August.

Expansion of marine heatwaves

The report calculated that elevated baseline temperatures expanded severe marine heatwave conditions across European waters. In 2026, severe marine heatwaves covered approximately 90% of the Bay of Biscay and Iberian coastal zone and 80% of the western Mediterranean. In an environment without anthropogenic climate change, the affected areas in both regions would have remained near 40%. The eastern Mediterranean saw 70% of its surface affected by heatwaves compared to an expected 9% in an unheated climate, while the Celtic Sea reached 80% coverage rather than 30%. In the Celtic Sea off Britain and Ireland, the observed extreme temperatures would occur only once per century without human influence.

Disruption to marine life and fisheries

Elevated water temperatures directly threaten marine ecosystems by inducing mass mortality among habitat-forming species such as corals, sponges, and macroalgae. These disruptions propagate through food webs, altering prey availability for marine mammals and seabirds. In southwestern England, fishers reported an influx of the common octopus (Octopus vulgaris), a species native to warmer North African waters, while cetaceans were observed feeding on jellyfish following declines in mackerel populations. The study warned that persistent thermal stress could lead to the collapse of commercial fisheries for cod, haddock, mackerel, scallops, and lobster.

We are rapidly approaching the absolute biological limits of adaptation for many species.

Terrestrial feedback and coastal conditions

The accumulation of heat in coastal waters directly affects weather patterns along European shorelines. Warmer sea surfaces elevate humidity and prevent nighttime air temperatures from cooling, compounding heat stress for coastal populations. In the Gulf of Valencia, sea surface temperatures approached 30 °C continuously, failing to drop below that threshold over a 24-hour period. Jorge Olcina of the University of Alicante noted that high sea temperatures accompanied inland alerts of up to 44 °C across Valencia and northern Alicante. In addition to compounding summer heatwaves, warmer waters increase atmospheric moisture that can intensify storms later in the autumn and winter.

This has the potential to completely reshape ecosystems that coastal communities rely on for food and income, and drive damaging extreme weather on land too.