“But you don’t notice them because they are green and less numerous,” he told Le Parisien.

“They live off carbon dioxide and light. Then come bacteria that eat them.

“It’s when the sun’s rays become very strong, starting in May, that they create a shield of red molecules that play the same role as sun cream.”

He and experts from several French scientific institutions - CNRS, CEA, Meteo France and Inrae - decided to try to work out how they survive and why “glacier blood” has thrived in recent years.

To do so, they took samples from soil found in five peaks at various altitudes to create a snow bloom map.

“To date, and to our knowledge, no such systematic investigation has been attempted,” they said.

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After studying their DNA, they found a variety of algae including one key blood-red type appropriately named Sanguina, which only grows above 1980 metres.

Algae produce a large amount of the world’s oxygen through photosynthesis, and are present at the root of most food chains. However, in certain conditions they multiply wildly, causing toxic sludge, for example.

Here, the experts believe that the snow algae may be a marker of climate change but also that their rise could hasten the shrinking of glaciers and snow caps.

“Unfortunately, the red colouration favours the melting of glaciers by getting rid of the snow’s ‘albedo’ effect [the amount of radiation reflected away as opposed to absorbed]: it reflects the sun’s rays less, and heats up and melts more quickly,” said Marechal.

“In areas without glaciers, it shortens periods of snow cover with cascading consequences on [water] supply to dams and farming irrigation in the plains.”

“It’s a paradox,” he went on. “The more the micro-algae multiply, the more they contribute to the disappearance of their own environment.”

The researchers have taken some species back to the lab to deepen their investigation into what triggers the blood-red blooms.

Marechal’s team is about to take fresh findings to see how they have been affected by large quantities of sand blown from the Sahara onto Alpine peaks due to particularly strong sandstorms this year.

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There may be, however, one silver lining to the rise of such bloody snow algae, according to the researchers.

“Sanguina molecules are rich in antioxidants and could interest the health sector to fight against the ageing of cells, or even energy to synthesise new fuels,” said Marechal.

The Telegraph, London