BrainStuff Classics: What Is Red Snow?

Snow usually appears white, but it can come in a few other colors -- and in the case of red snow, that vibrant color may be a warning from Mother Nature. Learn why in this classic episode of BrainStuff, based on this article: https://science.howstuffworks.com/nature/climate-weather/atmospheric/amazing-and-alarming-science-behind-red-snow.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of I Heart Radio. Hey
brain Stuff, Lauren Bogle bom here with a classic episode
for you today about the strange phenomenon of red snow,
also called watermelon snow, pink snow, or blood snow. This
is a phenomenon where snow appears pink to red in
streaks and patches due to the growth of a species

(00:25):
of algae, and aside from being visually striking, it's actually
fairly concerning. Hey brain Stuff, Lauren Bogle bomb here. Normally
snow looks white. This is because the ice crystals that
make up clusters of snow reflect and scatter every color
frequency in the visible light spectrum. So when sunlight bounces

(00:46):
off of a snow bank, all those colors blend together,
giving the snow a white appearance, or at least that's
what usually happens. Every so often, though mother Nature throws
us a curveball with a blanket of non white snow.
Plenty of the ld Or was a Roman naturalist who
lived from twenty three to seventy nine. In one of
his books, he wrote about red tinted snow, which ancient

(01:07):
travelers sometimes encountered. His hypothesis was that snow changes color
as time goes by, like a rusting piece of iron
snow itself. Plenty wrote Reddens with old age, and reports
of crimson colored snow kept pouring in over the next
to millennia. To figure out what's really going on, we
spoke via email with climate scientist Randall's Serveny. He reports

(01:29):
people in the dark and Middle Ages were often freaked
out by it. A professor at Arizona State University, Serveny
dedicated an entire book to weird weather stories in two
thousand five, titled Freaks of the Storm. It includes a
passage on red snow. As Serveny points out, there Charles
Darwin himself once came across white snow in the Andes
Mountains that turned blood red as it thawed. Another important

(01:50):
figure who witnessed the tinted precipitation was Sir John Ross,
a British naval officer and Arctic explorer. A reddish or
pinkish snow isn't just a historical curiosit city it's still
being observed. In February, for instance, a puddle of red
water that turned out to be melted vermillion snow was
found in Glacier National Park, So what's the mechanism behind this?

(02:13):
In some cases, scarlet dust may be a contributing factor.
Servini said. Many of the historic blood snows of Europe
are associated with moisture mixing with red Saharan dust that's
blown northward into Europe, which then falls out as either
red rain or snow. But it turns out that more
often than not, red snow is the product of algae,

(02:33):
and as scientists have learned recently, the stuff is also
contributing to climate change. We've known for some time now
that red or pink snow is generally caused by select
types of green algae, including these species Clematomonas novellis. These
life forms live in high altitude snow fields around the world.
Although they're technically green in color, the algae produce a

(02:54):
red pigment during the warm seasons. Doing so helps protect
the organisms from excessive solar radiation. We also spoke with
biologist Arwin Edwards, a research fellow at eberyest With University
in Wales. He said, I think of the red pigment
as a sunscreen. He explained the life cycle of this
and related types of algae. During the winter, the organisms

(03:14):
go dormant. Once spring arrives, they make their way toward
the surface of the snow and then bloom. But in
order to grow, the life forms need liquid water in
the form of wet snow in order to photosynthesize. This
is another reason why the red pigment is so useful.
Dark colored objects absorb more heat than light colored ones.
In snowy field where clematomotis is present, you'll find dense

(03:36):
communities of the microorganisms. A single millimeter that's point zero
three inches of snow can contain five hundred thousand of
these life forms. So in a large cluster of the
algae starts to release red pigment and mass, they darken
the snow they're living in. As a result, the snow
itself adopts a pinkish look. It also begins to melt.
So is this a cause for concern? In twice sixteen,

(03:59):
each tonal Nature published a report written under the leadership
of Stephanie Lutts, then a scientist at the University of Leeds.
Edwards was one of her co authors. After looking at
forty samples of the scarlet material from glaciers in Iceland, Norway,
Greenland and Sweden, the researchers reached a harrowing conclusion. Edwards said,
our paper is one of the first of several which

(04:20):
have identified a five to fiftcent acceleration of glacier melting
rates as a result of algae on the glacier surface,
a biological darkening effect. Put another way, glacial snow melts
five to fifteen percent more rapidly when Clementomonus or similar
types of algae are present, and that's not good news.
University of Bristol glaciologist Alejandra Anisio was a co author

(04:43):
on that Nature paper. Summing up the problem in an
email exchange, he said, basically, because of the darker coloration
of snow with the presence of the algae, the snow
absorbs more of the solar radiation, which increases pretension of
heat and melting of the snow. The process is not
in significant and must be taken into account if we
want to understand how fast glaciers and ice sheets will

(05:05):
melt with global warming. Also, there may be a self
perpetuating feedback loop at work here. The red tinted algae
melts snow, which enables more of the algae to grow,
which leads to even more melted snow and so on.
But let's shift gears for a moment and talk about
one of the red snow's weirdest qualities. It's scent. People

(05:25):
who come across the algae laden snow sometimes report that
it has a sweet, watermelon like scent. For the record,
Edward says he's never detected the odor himself, but that
it's probably the byproduct of those red pigments. Some popular
science writers have also advised against eating red snow because
it has been reported to cause gastric problems, perhaps due
to the algae other decaying material or mineral dusts and

(05:49):
snow can come in other colors as well. In January eighteen,
Central Kazakhstan received a layer of black tinted snow. This
may have been the result of industrial pollution. Additionally, there
are some types of algae that create yellowish snow. Of course,
as any third grader or dog owner can tell you,
that's not the only way to get yellow snow. Today's

(06:14):
episode is based on the article the Amazing and Alarming
science behind red Snow on how stuff Works dot com,
written by Mark Mancini. Brainstuffs production of My Heart Radio
in partnership with how Stuff Works dot com and it's
produced by Tyler Clang. Four more podcasts from My Heart
Radio visit the heart Radio app, Apple Podcasts, or wherever
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