Climate change is causing Antarctica's snow to turn green, study says

In coastal Antarctica, some snow isn't white — it's green. And while small amounts of the green snow have been visible for years, it's starting to spread across the continent because of climate change.

According to a study published Wednesday in the journal Nature Communications, the vibrant color is caused by microscopic algae blooming across the surface of the snow. Using satellite data and fieldwork observations, a team of researchers at the University of Cambridge and the British Antarctic Survey have created the first large-scale map of the green algae and predicted the future spread of the bizarre snow. 

Green snow appears along the Antarctic coast, growing in "warmer" areas, where the average temperatures reach just above freezing in the summer. Although the individual algae are microscopic, when they grow at scale, the green snow can even be seen from space. 

For the study, the team combined on-the-ground research from two summers in the Antarctic Peninsula with images from the European Space Agency's Sentinel 2 satellite taken between 2017 and 2019. In total, the team identified over 1,600 separate algal blooms on the snow surface. 

The team found that the distribution of green snow algae is strongly influenced by marine birds and mammals, because their excrement works extremely well as fertilizer. Over 60% of blooms were found near penguin colonies, and others were found near birds' nesting sites. 

"This is a significant advance in our understanding of land-based life on Antarctica, and how it might change in the coming years as the climate warms," lead author Dr. Matt Davey of the University of Cambridge said in a press release.

If bird populations are strongly affected by climate change, as they likely will be, the algae could lose key sources of nutrients. But the results of the study indicate that green snow will massively spread as global temperatures rise.

That's because in order to flourish, the organisms need an available supply of water. Temperatures on the peninsula where the green snow is found have risen dramatically in recent decades, increasing the amount of water available.

As the planet warms and more of Antarctica's snow melts, the algae will spread, the scientists said. And while some algae will be lost to areas that lose snow altogether, much more will be gained.

"As Antarctica warms, we predict the overall mass of snow algae will increase, as the spread to higher ground will significantly outweigh the loss of small island patches of algae," said co-lead author Dr. Andrew Gray, of the University of Cambridge and the University of Edinburgh.

It's unclear how the spreading algae will affect the planet. It plays a key role in cycling nutrients and pulling carbon dioxide from the atmosphere through photosynthesis, Davey said, but also darkens snow, and absorbs more heat from the sun.

The amount of algae found by the team creates a carbon sink that absorbs about 500 tons of carbon each year, the equivalent of about 875,000 average car journeys in the U.K., researchers said.

The amount of algae found is actually a conservative estimate, because the satellite was only capable of picking up green algae, missing its red and orange counterparts. "The snow is multi-colored in places, with a palette of reds, oranges and greens — it's quite an amazing sight," Davey said.