On 21 June, the global average sea surface temperature hit 21.0°C, according to data from the Copernicus Climate Change Service (C3S) and the Copernicus Marine Service (CMEMS). This surpasses the previous records of 20.83°C in 2023 and 20.86°C in 2024 by a tenth of a degree. While the margin may seem small, even slight temperature increases can have profound consequences for marine ecosystems, sea level rise, and the frequency of extreme weather events on land.
The record comes as El Niño conditions began developing in the Equatorial Pacific on 2 June, but scientists stress that the underlying trend is driven by long-term climate change. Over the past three years, ocean temperatures outside polar regions have been between 0.35°C and 0.73°C above the long-term average, according to Copernicus. Carlo Buontempo, Director of the Copernicus Climate Change Service at the European Centre for Medium-Range Weather Forecasts (ECMWF), warned: “Current conditions could indicate the beginning of a new phase, leading, once more, to uncharted territory. With ocean temperatures at these levels and El Niño on the horizon, we are likely to see more temperature records fall in the coming months.”
What Warmer Oceans Mean for Europe
Rising sea surface temperatures do not stay confined to the water. Warmer oceans heat the atmosphere, providing extra energy to storms and increasing evaporation, which can lead to heavier rainfall and flooding. This is particularly relevant for European coastal cities such as Rotterdam, Hamburg, and Venice, which are already grappling with sea level rise. The additional heat also accelerates ice melt, as seen in the Swiss glaciers hitting record early melt during the current European heatwave.
Marine heatwaves, which are becoming more frequent and intense, disrupt fisheries and coastal economies. They can also amplify heatwaves on land, as the warm ocean acts as a heat reservoir. This feedback loop is already evident in the extremely unusual heatwaves across Europe that Copernicus has warned about, with no immediate relief in sight.
Climate scientist Friederike Otto of Imperial College London, who was not involved in the Copernicus analysis, cautioned that any extended period above 1.5°C warming threatens “a whole range of extreme weather events that exceeds anything we’ve experienced in the past.” She also warned against overemphasizing the role of El Niño: “It comes and goes. Climate change on the contrary gets worse as long as we do not stop burning fossil fuels.”
The record ocean heat aligns with recent UN projections, which estimate a 91% chance that at least one of the next five years will exceed the 1.5°C warming threshold set by the Paris Agreement. The UN also forecasts an 86% probability that one of those years will surpass 2024 as the hottest on record. For Europe, this means preparing for more intense storms, coastal flooding, and heatwaves that strain public health systems—as highlighted by the WHO Europe chief urging governments to treat extreme heat as a health emergency.
The implications extend beyond the environment. Fisheries from the North Sea to the Mediterranean face disruption, while tourism-dependent regions like the Adriatic coast and the Greek islands may see altered seasons. As Buontempo noted, the world is entering uncharted territory—and Europe, with its densely populated coastlines and aging infrastructure, is on the front line.
