Why ocean warming matters for landlocked countries such as Switzerland

The warming of the oceans has negative consequences for marine life. Keystone

The seas have never been this warm since records began. Rising ocean temperatures also affect life in land-locked countries.  

A refreshing dip in the sea? For swimmers who spent their August holidays in Mallorca, that was probably not the case. A buoy off the Balearic island logged a record temperature of 33°C, only a few degrees below a hot bath at home. 

“For the Mediterranean, this is truly an extraordinary temperature record,” Thomas Frölicher, professor of climate and environmental physics at the University of Bern, told Swissinfo. 

The anomaly is not limited to the Mediterranean, where in some areas water temperatures reached up to 6°C above the seasonal average. Globally, the average sea surface temperature reached 21.1°C this summer, surpassing the record set in 2024, the hottest year since measurements began, according to CopernicusExternal link, the European Earth observation programme. 

However, ocean warming, which has now reached 1.1-1.2°C 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. 

“What worries me most is that today’s exceptionally high ocean temperatures will become the norm within ten or 20 years,” Frölicher says. The most fragile ecosystems risk exceeding their capacity to adapt, triggering cascading effects on biodiversity, fisheries, food security and coastal communities. 

The chart below shows how average ocean surface temperatures have now reached record levels. 

>> The following graph shows how the average ocean surface temperature has now reached record levels:

climatereanalyzer.org

Why are seas and oceans getting warmer? 

The main cause of warmer seas is greenhouse gas emissions. Carbon dioxide (CO₂), methane, and other gases trap heat in the Earth’s atmosphere. The oceans absorb more than90%External link of this excess heat generated by human activities. 

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 2023-2025External link. About a decade ago, a marine heatwave in the northeastern Pacific lasted nearly a year, Frölicher notes. 

Warming is not limited to the ocean surface. As Frölicher 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. 

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 studyExternal link by World Weather Attribution (WWA), an international group of experts that analyses the role of climate change in extreme weather events. 

“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 Frölicher, one of the study’s co-authors. 

What impact does El Niño have on ocean temperatures? 

El Niño 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. 

El Niño plays an important role because it redistributes heat between the tropical Pacific and the atmosphere, Frölicher 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 studyExternal link, El Niño events are now more extreme than in the past 1,000 years. 

How do warmer oceans influence climate and weather in Europe? 

What happens in the ocean does not stay in the ocean, the United Nations University Institute for Environment and Human Security (UNU-EHS) remindsExternal link us.  

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. 

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. 

In Europe, unusually warm Mediterranean waters have been linked to extreme rainfall events. One example is the floods that struck the Spanish city of Valencia in 2024External link. 

There is a link between the warming of the Mediterranean and the floods in Valencia in 2024. Keystone

Why do rising ocean temperatures matter to a landlocked country such as Switzerland? 

High Mediterranean temperatures increase evaporation and enrich the atmosphere with heat and moisture. When these air masses reach southern Switzerland, they can encourage episodes of intense rainfall, Frölicher explains. A similar process can also occur in the North Atlantic: if particularly warm, moisture-laden air is transported toward Switzerland and encounters the Alps, it can trigger heavy precipitation. 

“This does not mean that every storm and every episode of intense rainfall in Switzerland is caused by high sea surface temperatures,” the professor stresses. However, warmer seas do increase the risk of extreme rainfall events in Switzerland as well. 

Research is currently underway to better understand the relationship between sea surface temperatures and episodes of extreme precipitation in Switzerland. 

>>In Switzerland, global warming is proceeding at twice the global average rate:

What effects do rising ocean temperatures have on marine ecosystems? 

Exceptionally high sea surface temperatures and marine heatwaves have “devastating consequences for marine ecosystems”, WWA warns. They are responsible for mass mortality events among key species such as corals, sponges, and macroalgae (seaweed). 

In the Mediterranean, exotic and sometimes invasive species such as lionfish are spreading and may disrupt ecological balances, Guido Gnone, scientific coordinator of the Genoa Aquarium, told Swiss public broadcaster RSIExternal link. While some species may gain new opportunities for expansion, such as the Mediterranean’s most common sea turtle (Caretta caretta), climate change overall risks causing a significant loss of biodiversity, according to Gnone. 

Thomas Frölicher agrees.“Some fishing sectors in northern regions could benefit from the migration of species,” he says. “However, if we look at the situation on a global scale, the balance is negative.” The highest price will be paid by countries in the Global South, which depend heavily on fisheries both as a source of income and as a vital food resource.

What are the impacts of ocean warming on human health? 

According to WWA, rising marine temperatures encourage the spread of waterborne diseases such as vibriosis. In addition, jellyfish blooms, favoured by the new environmental conditions, can negatively affect beach tourism and lead to the temporary closure of some beaches. 

How can we adapt to ever-warmer seas? 

Phasing out fossil fuels and reducing greenhouse gas emissions is the most effective way to limit ocean warming and reduce future impacts. 

At the same time, adaptation measures are also needed. According to UNU-EHS, establishing marine protected areas, managing fisheries sustainably, and restoring coastal ecosystems such as mangroves are among the solutions that can strengthen ocean resilience. 

“People often underestimate the fact that ocean warming is not simply a short-term phenomenon or one confined to the surface,” says Frölicher. “The heat that is accumulating in the oceans will remain there for centuries.” 

The oceans remain one of our greatest allies in regulating Earth’s climate and mitigating global warming. How effectively they can continue to play that role will also depend on the choices we make today. 

Edited by Gabe Bullard /VdV/ds/ts