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Why snow is turning pink at high altitudes

AYESHA RASCOE, HOST:

You've heard of white snow, maybe even gray snow, but what about pink snow? High up in the mountains across the U.S., rapid growth of algae, or algal blooms, are turning melting snow pink. They further darken the surface of the snow and make it melt more quickly, and scientists are trying to understand what's causing them and how they impact water levels in drought-prone areas. One of those scientists is Robin Kodner, an associate professor of environmental science at Western Washington University. And she's here to talk with us today. Welcome to the show.

ROBIN KODNER: Thank you.

RASCOE: So first, where does the pink color come from?

KODNER: So when the algae cells are growing in the snow, they produce a red-colored pigment that turns the snow pink, or if the algae are in really high numbers, they can turn the snow red. And that pigment helps act as, like, a sunscreen for the algae. It helps protect them from high light levels.

RASCOE: How does the pigmented algae affect the snow?

KODNER: So the melting snow habitat is natural for the algae. However, if they're growing at really high concentrations, they darken the snow's surface, which increases the amount of solar radiation absorbed by the snow. And that then increases the rate of snow melt.

RASCOE: Are these blooms becoming more common? 'Cause you said it's not unusual to have the algae there, but is it new?

KODNER: That's an excellent question, and I feel like, as a scientific community, we're still trying to figure that out. There haven't been that many people around the world studying snow algae, but we'd predict that they would be getting worse or more intense as the climate warms and snowpack and glacier snow melts more regularly and earlier in the season. But we're still collecting the data to say for sure.

RASCOE: Does the speed of the snow melt matter for resources? Like, how does it affect that?

KODNER: So when snowpack melts, it provides water resources through rivers to downstream ecosystems and communities. And if the snow melts very quickly in spring or summer months, you can get flooding events and then droughts later in the season. So the rate of snow melt can impact how much water is available throughout the summer season.

RASCOE: So it sounds like if the blooms are getting larger, that may not be a good thing?

KODNER: Yeah. I feel like it's difficult to say good or bad. If snow algae blooms are increasing over time, and in particular if they're increasing on snow that's protecting glaciers in the summer, then it could be considered sort of a harmful bloom.

RASCOE: I understand that your lab has a project now where you're asking people to submit samples and photos when they think they see pink snow. Can you tell us a little bit about that? Like, what are you hoping to use that data for?

KODNER: We need a large data set, and so the best way to create this data set is to get help from the community. And people are out hiking and climbing and backcountry skiing all the time, and they are the eyes of this project. And so through the app that we created, people can make an observation when they think they see pink snow and take a picture and send it to us.

RASCOE: What's the name of the app?

KODNER: The app is called the Living Snow Project, and this type of data allows us to survey across large areas over long periods of time to address the question, are they changing? Are things getting worse?

RASCOE: That was Robin Kodner, associate professor of environmental science at Western Washington University. Thanks so much for speaking with us today.

KODNER: Thank you. Transcript provided by NPR, Copyright NPR.

Ayesha Rascoe is a White House correspondent for NPR. She is currently covering her third presidential administration. Rascoe's White House coverage has included a number of high profile foreign trips, including President Trump's 2019 summit with North Korean leader Kim Jong Un in Hanoi, Vietnam, and President Obama's final NATO summit in Warsaw, Poland in 2016. As a part of the White House team, she's also a regular on the NPR Politics Podcast.