Why record ocean warming matters to landlocked Switzerland

33°C in the Mediterranean brought the ocean’s heat into sharp focus this summer. A buoy off the Balearic Islands recorded the temperature during August, just a few degrees below a hot bath. The reading marked an extraordinary peak for the Mediterranean, according to Thomas Frölicher, professor of climate and environmental physics at the University of Bern.

The heat extended well beyond one Spanish measuring point. Some Mediterranean areas reached up to 6°C above the seasonal average, while the global average sea surface temperature climbed to 21.1°C during the summer of 2026. That surpassed the previous record, set in 2024, which was also the hottest year since measurements began, according to the European Earth observation programme Copernicus.

Switzerland has no coastline, yet its weather and water systems sit inside the same climate system. Warmer seas add energy and moisture to the atmosphere, influence air circulation and help shape weather arriving over Europe. They also expose Swiss holidaymakers, food supply chains and neighbouring coastal economies to mounting risks.

Frölicher’s warning is direct: temperatures that currently appear exceptional could become normal within 10 to 20 years. The Mediterranean is close enough to Switzerland for changes there to matter well beyond the beach.

More than 90% of the excess heat produced by human activity enters the oceans. Carbon dioxide, methane and other greenhouse gases trap energy in the atmosphere. The sea absorbs most of that energy, delaying some atmospheric warming while steadily changing marine conditions.

The heat does not remain at the surface. It accumulates through the upper 2,000 metres of the ocean, with measurements around Antarctica and in the North Atlantic indicating that deeper waters are warming as well. This stored energy can persist for years and influence weather patterns after the original emissions have entered the atmosphere.

Marine heatwaves are also becoming more frequent, more intense and longer lasting. Across European ocean waters, the share affected by these events rose from an average of 40% in the 1980s to 98% between 2023 and 2025, according to the European State of the Climate 2025 report.

The trend reflects fossil fuel combustion, especially the burning of coal and oil. A World Weather Attribution study concluded that climate change is driving the exceptional temperatures recorded in European seas. Frölicher, who co-authored the study, said each additional tonne of carbon pushes coastal ecosystems towards conditions they have not previously experienced.

Alpine weather does not stop at the shoreline. The Mediterranean and the North Atlantic influence the air masses that reach Switzerland. When warmer water evaporates, the atmosphere can carry more moisture. Weather systems then transport that moisture northwards, where mountains force air upwards and can intensify rain and snowfall.

A single warm sea cannot determine the outcome of every storm over Switzerland. Weather depends on several interacting factors, including atmospheric circulation, local topography and seasonal conditions. Ocean warming changes the background conditions in which those systems develop.

For the Alps, that matters in several ways. More intense precipitation can increase the pressure on rivers, slopes and urban drainage systems. Warmer winters can shift precipitation from snow to rain at lower and middle elevations, while a changing snowpack affects tourism, hydropower and summer water availability. The same Alpine catchments also feed rivers that cross national borders.

Switzerland’s exposure therefore includes more than direct coastal impacts. Cantons such as Valais, Ticino and Graubünden face different combinations of flood, drought, glacier and landslide risks. Ocean conditions help shape the large-scale climate that these cantons must manage, even though the nearest coast lies far beyond the Swiss border.