The anomaly is not limited to the Mediterranean, where in some areas water temperatures reached up to 6\u00b0C above the seasonal average. Globally, the average sea surface temperature reached 21.1\u00b0C this summer, surpassing the record set in 2024, the hottest year since measurements began, according to Copernicus<\/a>, the European Earth observation programme.<\/p>\n However, ocean warming, which has now reached 1.1-1.2\u00b0C above pre-industrial levels, goes far beyond uncomfortable swimming conditions. Its consequences extend to marine ecosystems and to the climate of land areas, including countries far from the coast, such as Switzerland.<\/p>\n “What worries me most is that today’s exceptionally high ocean temperatures will become the norm within ten or 20 years,” Fr\u00f6licher says. The most fragile ecosystems risk exceeding their capacity to adapt, triggering cascading effects on biodiversity, fisheries, food security and coastal communities.<\/p>\n Why are seas and oceans getting warmer?<\/p>\n The main cause of warmer seas is greenhouse gas emissions. Carbon dioxide (CO\u2082), methane, and other gases trap heat in the Earth’s atmosphere. The oceans absorb more than90%<\/a> of this excess heat generated by human activities.<\/p>\n As on land, marine heatwaves are becoming more frequent, more intense and longer lasting. The share of European ocean waters affected by these events has increased from an average of 40% in the 1980s to 98% during the period 2023-2025<\/a>. About a decade ago, a marine heatwave in the northeastern Pacific lasted nearly a year, Fr\u00f6licher notes.<\/p>\n Warming is not limited to the ocean surface. As Fr\u00f6licher explains, heat is accumulating throughout the ocean, particularly in the upper 2,000 metres. Measurements around Antarctica and in the North Atlantic indicate, however, that deep waters are also gradually warming.<\/p>\n Climate change, and in particular the burning of fossil fuels such as coal and oil, is the primary driver of rising temperatures in European seas, according to a new study<\/a> by World Weather Attribution (WWA), an international group of experts that analyses the role of climate change in extreme weather events.<\/p>\n “Every additional tonne of carbon we emit [into the atmosphere] pushes European coastal waters and ecosystems toward conditions that have never been experienced before,” says Fr\u00f6licher, one of the study’s co-authors.<\/p>\n What impact does El Ni\u00f1o have on ocean temperatures?<\/p>\n El Ni\u00f1o is a natural, cyclical climate phenomenon that causes an abnormal warming of surface waters in the equatorial Pacific Ocean. This year’s event is particularly intense, possibly the strongest ever recorded.<\/p>\n El Ni\u00f1o plays an important role because it redistributes heat between the tropical Pacific and the atmosphere, Fr\u00f6licher explains. “As a result, global sea surface temperatures temporarily rise even more than they would from the effects of global warming alone.” According to a recent study<\/a>, El Ni\u00f1o events are now more extreme than in the past 1,000 years.<\/p>\n How do warmer oceans influence climate and weather in Europe?<\/p>\n What happens in the ocean does not stay in the ocean, the United Nations University Institute for Environment and Human Security (UNU-EHS) reminds<\/a> us.<\/p>\n The oceans surrounding Europe play a crucial role in shaping the continent’s climate and weather patterns. The North Atlantic influences atmospheric circulation through the prevailing westerly winds, while variations in sea surface temperatures directly affect rainfall patterns.<\/p>\n Warmer seas provide more energy and water vapour to storms, increase evaporation, and can lead to heavier and more intense rainfall over land. They can also influence monsoons and increase the destructive potential of tropical cyclones.<\/p>\n
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