Climate change added up to two degrees to European sea temperatures in July

Attributing extreme ocean warmth

Human-caused climate change was the primary driver of record sea surface temperatures across Europe during the summer, according to an attribution study released on Wednesday by the World Weather Attribution group. Researchers combined observational measurements with climate model simulations to determine how greenhouse gas emissions altered sea temperatures across four European marine sectors. The analysis concluded that the peak sea surface temperatures observed across the eastern and western Mediterranean, the Bay of Biscay, and the Iberian coast would have been virtually impossible without global warming. In the Celtic Sea off the coasts of Britain and Ireland, temperatures of this magnitude would have occurred only about once a century in a world without climate change.

Our research shows clearly that this is being driven by climate change, in particular by the continued burning of fossil fuels.

Regional heat across European waters

The Mediterranean Sea experienced its warmest July on record, reaching an average surface temperature of just over 27 degrees Celsius. In early August, an offshore buoy west of Mallorca registered an open-water measurement above 33 degrees Celsius, while localized Mediterranean zones measured more than 6 degrees Celsius above seasonal averages during the hottest two weeks of July. Catherine Gregory and fellow researchers calculated that climate change added 2.0 degrees Celsius of warming directly to both Mediterranean basins. Western European and Iberian coastal waters experienced an estimated 1.4 degrees Celsius of warming, while seas around Ireland warmed by 1.3 degrees Celsius due to fossil fuel emissions.

Ecological and coastal disruptions

Marine heatwaves spread across 90% of the Bay of Biscay and Iberian coastal region and 80% of the Western Mediterranean during the summer. According to statistical modeling from the team, only around 40% of those areas would have experienced marine heatwave conditions in the absence of the 1.4 degrees Celsius of baseline warming accumulated since pre-industrial times. These elevated temperatures disrupt marine food chains, harm coastal fisheries, and increase jellyfish populations. Marine organisms face severe survival pressures, with coral reef die-offs occurring after temperature anomalies of just 1.0 degree Celsius above baseline thresholds.

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

Atmospheric baselines and storm risks

The heating of surrounding European seas has direct consequences for weather patterns on land and for coastal economies. Elevated sea surface temperatures raise atmospheric humidity and boost overnight temperatures in coastal communities, increasing risks from extreme heatwaves. The World Weather Attribution consortium noted that the Mediterranean Sea is warming at twice the speed of the global ocean average. Data from the Copernicus Climate Change Service showed that worldwide ocean temperatures established peak values for a second consecutive month in July. The thermal energy stored in Europe's oceans also creates conditions capable of intensifying storm systems later in the year.

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.