Mountains are one of the first thermometers on the planet: they respond earlier, do so intensely and more visibly than any other terrestrial ecosystem to global warming. What begins happening at its summits anticipates what will come later to the rest. The Pyrenees are no exception, in fact they work like a huge natural laboratoryone of the most documented in Europe. And the data they provide is anything but good.
He Bulletin of Climate Change Indicators of the Pyrenees prepared annually by Meteocat and coordinated by the Pyrenean Climate Change Observatory (OPCC) confirms it: the warming of the mountain range is not something punctual, but structural.
What is happening in the Pyrenees. That they are warming asymmetrically and accelerated, with summers exploding at a rate that doubles the rest of the year, which has direct and different consequences on the ecosystem. Jordi Cunillera, head of the Meteocat climate change team, goes even more into detail: on the southern slope the trend is also drier, adding additional water pressure on the southern ecosystems.
In data. The list of indicators and the 65 years of monitoring show clear and worrying trends.
From 1959 to 2024:
- Increase in average annual temperature of 1.9 °C.
- By seasons: while in winter the increase has been 1.4 °C, in summer it has been almost double (+ 2.7 °C)
- Steady increase in tropical nights.
- There are 20 fewer days of frost and 32 more days of summer per year.
Every decade:
- There are 3 fewer days of frost with colder winters
- There are 4.9 more days of summer (temperature above 25 ºC).
- The temperature increases +0.30 ºC.
Why is it important. Firstly, because of the solidity of the research: it does not measure specific variability, but rather the structural and accumulated transformation of the Pyrenean climate over 65 years. The Pyrenees are a climatic island for alpine species that do not have the capacity to migrate further north or higher, a true gem in flora and fauna with endemisms particularly sensitive and vulnerable to changes in temperature. Thanks to its rugged terrain, it has been able to preserve certain spaces from direct human activity (from tourism to agriculture), but it cannot escape this indirect effect.
On the other hand, the Pyrenees are also a tap for southern Europe: the accumulated snow and ice feed rivers such as the Ebro, the Segre or the Garonne during the dry season, on whose flow millions of people, irrigated hectares and river ecosystems depend. It is true that precipitation remains stable, but if it gets hotter, water stress increases: evapotranspiration skyrockets, the soil loses moisture faster and terrestrial ecosystems enter a situation of progressive summer water deficit. The system becomes less resilient to disturbances, such as fires.
Context. The study is part of the work of the Pyrenees Working Community, which through the Pyrenean Climate Change Observatory seeks to unify the data of the Spanish, French and Andorran states through the LIFE project Pyrenees4Climate. This international cooperation effort is essential as ecosystems do not understand political borders and climate change requires joint actions. In addition to climate monitoring, its objective is to implement the Pyrenean Climate Change Strategythe first European initiative of its kind designed specifically for a transboundary mountain bioregion.
The project has established 16 key recommendations, including a “Pyrenean Forest Emergencies Protocol” to share cartography, meteorological data and crisis communication. The report highlights that differences in regulations between the three states slow down the response, which is why they urge the interoperability of physical means and improve protocols to be more resilient to climate change.
How they measure it. The scientific robustness of these results is based on the analysis of 12 temperature series and 26 high-quality precipitation series, strategically distributed throughout the mountain range. The different research teams use the period 1961-1990 as a historical reference to calculate anomalies and ensure that the observed trends are statistically significant.
The work team is led by Meteocat and has the collaboration of affected organizations such as AEMET, Météo-France, the Andorra Meteorological Service, IPE-CSIC or Euskalmet for a complete and unified view. Among the indicators studied are the average annual temperature, seasonal variation, frost days, summer days, tropical nights, warm and cold spells or water stress. These indicators respond to internationally standardized definitions by the World Meteorological Organization, which allows comparison with other European high mountain studies.
The impact on the ecosystem. One of the most serious effects is anoxia in mountain lakes: as surface water warms and winter ice reduces, the natural water mixing cycle is broken, leaving the bottom without oxygen. This phenomenon puts at risk the survival of invertebrates and microorganisms that are the base of the trophic chain in these sensitive aquatic ecosystems, something that is happening, for example. in the Ibón de Marboréin the Aragonese Pyrenees. The Pyrenean glaciers have lost 96% of their glacial surface since the 15th century and the future looks even darker: 4% are will be extinct by 2050.
On the other hand, the more intense heat is causing the snow to melt earlier due to the arrival of intrusions of Saharan dust associated with warm air masses from Africa: when dust particles are deposited on the surface of the snow, it absorbs more energy instead of reflecting it, thus accelerating its fusion, as explains Meteored. In addition to being a climatic indicator, the disappearance of the Pyrenean cryosphere means the irreversible destruction of a habitat and a hydrological function on which the entire chain of ecosystems rests, from high mountain lakes to wetlands many kilometers ahead.
In Xataka | The Pyrenees have become a huge meteorological laboratory: torrential rains have multiplied by four in Spain
Cover | jolumurcia and Myrabella
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