The reduced flow of the Cola de Caballo waterfall in Ordesa y Monte Perdido National Park, changes in forests and the accelerating retreat of glaciers are beginning to transform the Pyrenean landscape. Initial results from the LIFE Pyrenees4Clima project show significant impacts on the cryosphere, water resources and ecosystems. Climate change is also affecting less visible environments, such as ice caves and mountain lakes, while high-altitude climate refugia are emerging as essential areas for the survival of the most vulnerable species.
Climate change is profoundly altering the Pyrenees, and its consequences are already affecting human health, water availability, biodiversity, ecosystems, the economy and life across the region. These wide-ranging impacts also include the rapid transformation of some of the mountain range’s most iconic landscapes. The reduced flow of the Cola de Caballo waterfall in Ordesa y Monte Perdido National Park, the rapid retreat of glaciers and the disappearance of ice from caves are among the changes documented by the European LIFE Pyrenees4Clima project, led by the Pyrenean Climate Change Observatory (OPCC). The project began in 2024 and will run until 2031, working to strengthen the Pyrenees’ resilience to climate change through an integrated approach and demonstration actions on the ground.
“The intensity and duration of heatwaves, both globally and across the Pyrenean region, have increased over the past decade, and climate models indicate that this trend will continue as the planet grows warmer,” says Blas Valero, geologist and research professor at the Pyrenean Institute of Ecology (IPE-CSIC), one of the 47 partners in LIFE Pyrenees4Clima. Data from the latest Pyrenean Climate Change Indicators Bulletin (BICCPIR) show that, since 1960, the Pyrenees have lost three frost days per decade and gained 4.9 summer days.
Valero notes that “the increase in the frequency, duration and intensity of heatwaves across the planet is a direct consequence of climate change, as confirmed by attribution studies conducted by leading international meteorological agencies”. An analysis by the World Weather Attribution scientific group links the worsening of heatwaves in Europe to emissions from fossil fuels.
Glaciers, ice caves, lakes, headwater rivers, forests and alpine meadows are among the most vulnerable environments. “These iconic landscapes and ecosystems are undergoing rapid and irreversible changes as a result of global warming, accelerated by heatwaves,” explains Valero.
One of the clearest examples can be found at the Cola de Caballo waterfall in Ordesa y Monte Perdido National Park. “In this iconic landscape, the impact of climate change is evident,” says Luis Javier Lambán, a scientist at Spain’s Geological and Mining Institute (CN IGME-CSIC). The waterfall is fed by the Garcés spring, which drains the karst aquifer of the Monte Perdido massif. Its flow reaches a maximum of approximately 2,000 litres per second in June, coinciding with the snowmelt, and a minimum of around 400 litres per second in January.
Jorge Jódar, a scientist at CN IGME-CSIC, explains that “the impact of climate change is evident in the decline in spring flow during droughts or winters with low snowfall”. Hydrological models show a dramatic shift in the seasonality of aquifer discharge: baseflow increases in winter, falls considerably in summer, and the period of peak flow, which previously occurred in June and July, has moved forward by more than a month to May. This groundwater discharge is essential for conserving the national park’s biodiversity, ensuring water supply to its ecosystems, and maintaining the flow and temperature of watercourses in the lower areas of the massif.
Another clear sign is the accelerating retreat of the glaciers. They have lost more than 90% of their surface area since 1850, and their retreat has accelerated since 2022, reaching annual melt rates three times higher than those observed at the beginning of the 21st century. “Landscapes shaped by ice and snow in the Pyrenees are being significantly affected by recent climate trends,” says Jesús Revuelto, a researcher at IPE-CSIC.
Los efectos del cambio climático también se observan en los bosques y matorrales. Su superficie ha aumentado significativamente en las últimas décadas debido al abandono de los pueblos y a la reducción de las actividades tradicionales de gestión y aprovechamiento forestal. Sin embargo, este nuevo paisaje está cada vez más amenazado por las altas temperaturas, la falta de agua, las especies invasoras y el creciente riesgo de incendios. Rafael Delpi, de FORESPIR, afirma que los bosques de montaña son especialmente sensibles al déficit hídrico. Las sequías y las olas de calor no provocan por sí solas su decaimiento, pero contribuyen a debilitarlos y pueden desencadenar la desaparición o el desplazamiento de diferentes especies.
Studies conducted in forest plots show that droughts and heatwaves can trigger or worsen processes of forest decline. The strain placed on trees by high temperatures and water scarcity makes them more vulnerable to threats such as pests and fungi.
Signs of decline are already being observed in silver fir communities in different parts of the Pyrenees, both on the northern slopes, particularly in Aude, and on the southern slopes, in Navarre and Aragon. FORESPIR also warns that forest deterioration increases the amount of dry vegetation and combustible material, raising the risk of wildfires spreading.
Heatwaves can also encourage the spread of invasive species. Extreme temperature events increase mortality among some native species, creating space for non-native species that are more tolerant of high temperatures. Belinda Gallardo, a researcher at IPE-CSIC and lead author of the first comprehensive assessment carried out across the mountain range, explains: “We have identified more than 650 non-native species, three quarters of which are plants. Their presence has increased exponentially since 1980, with concentrations in valleys and along roadsides.”
The most concerning species include the American mink, tree of heaven, Asian hornet and box tree moth. The latter reached the Pyrenees from Asia in 2014 and causes defoliation and the death of boxwood, increasing the amount of dry material and the risk of fire.
The Pyrenees are also changing in their least accessible and visible areas. This is the case of the ice caves found at high elevations, whose ice deposits are rapidly disappearing. Over the past five years, some deposits formed thousands of years ago have vanished completely or decreased significantly in thickness. Ana Moreno, a researcher at IPE-CSIC, notes that the ice has almost entirely disappeared from several notable caves in Ordesa y Monte Perdido National Park.
One of the most striking cases is Sarrios 1 cave, where an ice deposit almost six metres thick and more than 5,000 years old melted as a result of the heatwaves of summer 2023. In other caves, such as Casteret and Sarrios 6, the ice is shrinking by more than 20 centimetres per year. Research is also documenting changes in Pyrenean mountain lakes, which have been monitored by IPE-CSIC since 2017. This monitoring has recorded an increase of up to 0.45°C per year in surface water temperatures.
Warming changes the periods during which the different layers of water mix and alters the cycling of nutrients and other elements. In Lake Marboré, a lack of oxygen in deep waters during winter has been recorded for the first time. Monitoring has also detected prolonged periods when surface water temperatures exceed normal levels. These lake heatwaves occur not only in summer but also in autumn and could affect the flora and fauna of these mountain lakes, although their impact has yet to be determined.
Climate change is also affecting air quality in the Pyrenees. One factor worsening its effects is the increase in Saharan dust and soot generated by wildfires. Saharan dust can provide nutrients to terrestrial and aquatic ecosystems, but it also accelerates melting. When it settles on snow and ice, it darkens their surface, causing them to absorb more heat and reducing how long they remain.
Jorge Pey, investigador del IPE-CSIC y responsable de las mediciones realizadas en Formigal-Sarrios, alerta de que “entre 2019 y 2025 el aire de los Pirineos muestra concentraciones de partículas cada vez mayores, relacionadas tanto con incendios forestales cercanos como con el transporte de contaminantes a grandes distancias”.
In summer, typical soot concentrations range from 200 to 300 nanograms per cubic metre. However, extreme episodes have been recorded since 2022: more than 2,500 nanograms per cubic metre in 2022, coinciding with the Añón de Moncayo wildfire; up to 4,000 in 2024, due to smoke from Canada’s megafires; and more than 5,000 in 2025, associated with the major wildfires in Castile and Galicia.
These data show that wildfires and the atmospheric transport of pollutants are having an increasing impact on the Pyrenees. Both phenomena are being intensified by climate change and could become more severe in the future. Jorge Pey notes that “2026 could set a record for summer soot concentrations due to the number, intensity and extent of wildfires in and around the Pyrenean region”.
Global warming and heatwaves are already affecting biodiversity, although their consequences vary from one species to another. Each species has a different capacity to move, withstand high temperatures or adapt to new conditions. “Climatic conditions are changing too quickly for many species to evolve and adapt where they currently live,” explains Begoña García, a researcher at the Pyrenean Institute of Ecology.
For this reason, climate refugia become a lifeline for plants and other organisms with little or no mobility. These small areas maintain more favourable conditions than their surroundings, such as lower temperatures or higher humidity. They are particularly abundant in mountain regions and are identified using miniature climate sensors, drone flights equipped with thermal cameras and flora inventories. García warns that biodiversity is too broad and complex to generalise: “If there are losers, there are also winners. Therefore, rather than speaking of a single overall effect, we need to identify which environments and groups of species are being affected most severely and which may see their future threatened.”
Research is beginning to show that many populations of the rarest, most distinctive and most vulnerable plants are found in well-preserved and often hard-to-reach mountain refugia. In these areas, they benefit from more favourable conditions for withstanding the effects of climate change.
Evidence gathered by LIFE Pyrenees4Clima shows that climate change is not causing a single impact, but a simultaneous transformation of snow, ice, water, biodiversity, air quality, forests and pastures across the Pyrenees. Many of these changes are already visible, while others can only be detected through ongoing scientific research and monitoring. Their effects also reinforce one another, amplifying the overall impact.
In response to this situation, LIFE Pyrenees4Clima is working to turn scientific knowledge into concrete adaptation measures. Through cooperation among its 47 partners and demonstration actions developed with territorial stakeholders across the mountain range, the project aims to anticipate risks, strengthen the response capacity of local areas, and preserve the ecosystems and resources on which the Pyrenean population depends and which sustain life far beyond the mountain regions.
Attached in the gallery are:
Figure 2: Glacier retreat at Monte Perdido and Aneto for the year 2024–2025
Figure 4: Example of heat waves at Lake Marboré during 2023, ranging from strong in intensity during the summer to even severe in early fall
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