Global ocean temperatures reach record high for June, Copernicus warns of severe weather and ecosystem strain

Record-breaking warmth

Global daily sea surface temperatures have surpassed the previous June records set in 2023 and 2024, the Copernicus Climate Change Service (C3S) and Copernicus Marine Service confirmed on 1 July. On 21 June, the C3S dataset recorded 20.86 degrees Celsius, just above the 20.83 degrees observed in the prior two years. The Copernicus Marine Service independently measured 21.0 degrees that day, 0.1 degree above its earlier record. The milestone was expected after the World Meteorological Organization declared the start of El Niño on 2 June, and it reflects both long-term human-driven warming and the natural climate pattern.

This record will have consequences on weather patterns, global climate, and marine ecosystems.

El Niño and long-term warming

Seasonal forecasts from C3S suggest the current El Niño may reach an intensity not seen in decades. The phenomenon warms the equatorial Pacific and typically pushes global temperatures higher. Carlo Buontempo, C3S director, cautioned that the planet is entering unfamiliar territory.

Current conditions could indicate the beginning of a new phase, which will lead, once again, into uncharted territory. With ocean temperatures at these levels and El Niño on the horizon, it is likely that in the coming months we will witness the surpassing of further temperature records.

Cascading impacts

Warmer oceans keep the atmosphere heated for longer, supply extra energy to storms, and increase evaporation, raising the risk of extreme rainfall and flooding. Ocean warming also accelerates sea-level rise and ice melt, stressing marine ecosystems. Higher sea surface temperatures are linked to more frequent and intense marine heatwaves, which alter ecosystems and fisheries, hit coastal economies, and can intensify extreme heat over adjacent land.

Europe heats twice as fast

Europe is warming at 0.56°C per decade since the 1990s, double the global average of 0.27°C, according to Copernicus data. Only the Arctic, at 0.75°C per decade, is heating faster. Experts point to three drivers: reduced snow cover exposes darker, more absorbent ground; the African anticyclone is more frequent, drawing hot air northward; and a large part of the Arctic, the fastest-warming region, sits within Europe's geographic domain. The Mediterranean Sea has been one to two degrees above normal all winter, and near Sardinia satellites have recorded surface temperatures up to 6°C above the 40-year average for late June.

Storms and heat deaths

The excess energy stored in the warm sea is already fueling severe weather. Massimiliano Pasqui, a CNR atmospheric physicist, explained that warm water primes the atmosphere for intense thunderstorms when cooler air arrives. Italian civil protection issued yellow or orange alerts for 14 regions on 30 June, anticipating violent storms and hail. The heat has also had a deadly toll: the World Health Organization reported more than 1,300 excess deaths in Europe linked to high temperatures since 21 June.

The heat of the sea is all energy ready to be released into the atmosphere.

A hotter, more dangerous future

Climatologists warn that such heatwaves will become longer and more frequent, with extreme temperatures potentially occurring three to six times per season. European cities are under pressure to adapt: expanding green spaces, increasing access to air conditioning, deploying renewable energy, and using heat-reflective materials. Buontempo’s warning leaves little room for comfort: with El Niño strengthening, further temperature records are probable in the months ahead.