Near the end of the season, researchers ran six field trials on snow around Formigal ski resort in Huesca. The tests found that microplastics increased melting by up to 17% in older, denser snow. Fresh snow showed little or no melting.
The teams came from Centro de Ciências do Mar do Algarve, CCMAR in Portugal, and Instituto Pirenaico de Ecología, IPE-CSIC in Spain. Each trial used four or five surface-snow plots. Researchers also tracked changes in albedo and snowpack structure.
Some plots received black polyethylene pellets with an average diameter of 0.3 millimetres. Others received black fragments measuring 0.45 millimetres. The fragments, taken from the wheels of a baby carriage, simulated tyre wear.
Researchers exposed the snow to the particles for about four hours. Each experiment also included untreated control plots.
The snow's starting condition mattered most.
Fresh snow had low density. As microplastic levels rose, the space between its grains warmed. Its albedo fell moderately, while its specific surface area changed substantially. Little or no melting occurred in these samples, much as in the controls.
Older snow responded differently. It was denser, and the season was nearing its end. As microplastic concentrations rose, melting rates reached as much as 17% above those in untreated plots.
The strongest effect emerged after the snowpack had already changed physically over time. That distinction matters.
Albedo measures how much solar radiation a surface reflects. Clean snow can reflect up to 90% of incoming sunlight. Impurities reduce that reflectivity, allowing the surface to absorb more energy.
The cryosphere stores close to 70% of the planet's fresh water. Snow and ice so affect water availability and heat regulation.
The particles stem from the global expansion of plastic production. More than 400 million tonnes are produced worldwide. Between 40% and 50% of newly made plastic has a useful life of less than one year.
Around 80% ends up in landfills or the natural environment. Larger pieces then break down into microplastics below five millimetres and nanoplastics below one micrometre. These particles can travel hundreds or even thousands of kilometres through the atmosphere or ocean currents.
The study is presented as the first experimental work to show how microplastics affect snow properties. Its findings point to different effects: fresh, low-density snow showed limited melting, while aged, dense snow melted faster.
More field research is needed. Future tests should cover other locations and run longer than one day, using a wider range of plastics.
The evidence supports a measured conclusion. Once microplastics reach mountain snow, they can affect it directly. Under specific conditions, they can change reflectivity and speed up melting. The size of the effect still depends on snow age and density.
The Central Pyrenees trials provide direct evidence of that risk. Further experiments must show how different particles behave across the global cryosphere. Until then, reducing plastic pollution and expanding field measurements offer the clearest ways to assess its contribution to snow loss and global warming.
