Pyrenees Losing Ice Days, Gaining Summer Days Amid Climate Change

The Pyrenees are losing three ice days and gaining 4.9 summer days each decade due to climate change, with southern slopes including Andorra showing the sharpest temperature rises and drying trends, according to the 'Boletín de Indicadores de Cambio Climático 2024'.

Produced under the European LIFE Pyrenees4Clima project and led by the Catalan Meteorological Service (Meteocat), the report draws on data from Andorra's Meteorological Service, Météo-France, Spain's AEMET, the Pyrenean Institute of Ecology-CSIC, and the Basque Meteorology Agency (Euskalmet). It analyzes trends from 1959 to 2024, using a 1961-1990 reference period, and records 20 fewer ice days (minimum temperatures below 0°C) and 32 more summer days (maximum temperatures above 25°C) across the range. Heatwaves have grown longer, cold spells shorter, and average annual air temperatures have risen 1.9°C since 1959—reaching 2.7°C in summer—with more tropical nights above 20°C in valleys. The years 2022-2024 were the warmest on record.

Southern areas, including stations in Ransol and Andorra la Vella, have warmed fastest at 0.31°C per decade. Rainfall there has dropped 2.5% every ten years, with broader Mediterranean Pyrenees seeing a 17.6% annual decline and nearly 25% in summer precipitation since 1959—contrasting stable levels on Atlantic-influenced northern slopes. Andorra, with 90% of its area under Mediterranean mountain climate, registered 2025 as its fourth-warmest year since 1950, behind only 2022-2024; its ten hottest years have all occurred in the last 20.

Lake warming compounds the changes. At Marboré Lake in the Aragonese Pyrenees, surface temperatures to 5 meters depth rose nearly 0.5°C over the past decade, driving lake heatwaves, reduced ice cover, and anoxia episodes harming fish and plants. In Andorra, Montmalús Lake has seen average temperatures increase 1°C since 1985 and stays ice-free longer in winter, heightening biodiversity risks as species reach altitudinal limits.

Saharan dust and smoke from Iberian wildfires, with 2025 peaks over 5,000 ng/m³, darken snow and ice, cutting albedo and accelerating melt—even on Andorran peaks. Meteocat climate team head Jordi Cunillera noted a "clear trend" toward a warmer Pyrenean climate, drier on the southern flank. Andorra's Office of Energy and Climate Change director Carles Miquel highlighted greater impacts at higher elevations, warning that warming lakes and shifting habitats threaten species unable to migrate upward further.

The bulletin, based on 12 temperature and 26 precipitation series, bolsters cross-border adaptation through the Pyrenean Climate Observatory (OPCC).