When we think of climate change, we quite rightly think of environmental degradation, pollution, warmer summers, tropical storms and fossil fuels. To address these issues, the consensus is to promote increased renewable energy use, primarily solar and wind power. Because those renewable energy sources suffer from intermittency issues, their contributions inevitably need to be supported by other means, a concern which has fuelled nuclear energy’s recent return to popularity. Hydroelectric plants, powered by rivers are another energy source that can complement solar and wind because they tend to produce more constant levels of electricity.
However, investors and the general public should be aware that even these energy sources are not immune to the effects of climate change. Given the increased incidence of droughts, the need for water to spin hydroelectric turbines and cool off nuclear reactors introduces climate change fragility into these energy production systems. Given the recent concerns raised by the blackouts in Spain and Portugal at the end of April, we should all be mindful of the constraints imposed by climate change on other energy sources going forward.
Drying Out Hydropower
Hydropower depends on consistent river flows and reservoir levels to turn turbines, which generate electricity. Climate‑induced droughts are an existential problem for this renewable energy source. Sadly, this is not new, and the risk has already materialised on several occasions and appears to be increasing in intensity.
During the first five months of 2025, European hydropower output dropped by 13%, in comparison to the same period in the previous year, hitting its lowest May level since 2017. Alpine snow-fed hydro potential was one-third below average, while the Danube catchment potential was 60% below normal. In Switzerland, the Aubonne hydroelectric plant closed a month earlier than usual this year on account of lower water levels. In Turkey, generation from three major dams along the Euphrates–Tigris basin has fallen by roughly 25% over the last decades. Projections suggest power generation will have fallen by another 30% to 40% by 2100.
According to the IEA, Norway relied on hydropower for 41.5% of its total energy supply in 2023. In Sweden, the figure falls to 12% and to 4% in Finland. Denmark produces no hydropower. Although there are no apparent cases of hydropower plant closures in the Nordics explicitly due to drought, climate-induced volatility is a developing concern. In Finland, modelling shows that during multi-year droughts, hydropower output could drop drastically.
Drought and Jellyfish Threaten Nuclear Power
According to the IEA, Sweden and Finland, the only Nordic countries that produce nuclear power, rely on this source for 26.7% and 27.6% of their total energy supply in 2023 respectively. Although Norway and Denmark produce no nuclear energy, this energy source is pertinent nonetheless. Nuclear power plants require large quantities of water for cooling, usually from rivers or seas, making them vulnerable to droughts and storms.
The problem has a long history. During Europe’s 2003 heatwave, a fourth of French reactors had to shut down due to cooling limitations. The Nordics, too, have witnessed instances of climate-related interruptions to nuclear power operations. During the heat wave of July 2018, Sweden’s Ringhals‑2 reactor was temporarily taken offline. Elevated cooling water temperatures in the sea of Kattegat exceeded the plant’s design limit of 25 °C. So far this year, at least France and Switzerland have had to shut down nuclear power plants for similar reasons. At the beginning of the summer, EDF shut down the Golfech nuclear power plant in France, and Axpo had to close the Beznau nuclear power plant in Switzerland.
However, climate change doesn’t just melt ice or dry rivers. Via global warming, it also alters the behaviour of our ecosystems. This was what Sweden’s Oskarshamn-3 reactor discovered in 2013 when a swarm of jellyfish overwhelmed its cooling water intake pipes. Given jellyfish’s tendency to surface in warmer waters, its resistance to increased levels of acidity and the decrease in their natural predators due to overfishing, “jellyfish attacks on nuclear power plants” are not merely a funny headline. Similarly, a jellyfish invasion clogged cooling intakes and forced four reactors at France’s Gravelines plant, causing it to shut down temporarily. Other climate-related safety concerns include threats from flooding, sea-level rise, heat waves, and coastal inundation, all of which put strain on reactor cooling systems and infrastructure.
Trying to Avoid Power Cuts
Although past performance suggests that we have managed to navigate the challenges that climate change has created for nuclear and hydropower, our ability to cope has not been costless. A 2023 report by the French Court of Accounts argues that there is a real possibility that climate change-related nuclear power cuts may increase by three to four times by 2050.¹ Concomitantly, studies of the effect of climate change on hydropower suggest divergent paths between Southern and Northern Europe, whilst Alpine regions might experience more volatility.
At a time when the benefits of these energy sources are being touted as helpful complements to solar and wind power, it is important to keep track of their limitations. As always, a holistic approach to the problem now may help us steer clear of embarrassing failures in the future.
¹Court des Comptes, March 2023, “L’adaptation au changement climatique du parc des réacteurs nucléaires” (page 71)
