National Geographic News
Photo of dust-covered snow on San Juan Mountains.

The snow in the San Juan Mountains in Colorado is covered in dirt in May 2009.

Photograph by NASA/JPL-Snow Optics Laboratory

Dennis Dimick

National Geographic

Published June 10, 2014

It's easy to imagine new snow so bright that we must avert our eyes even while wearing sunglasses. What scientists are discovering, though, is this brilliant whiteness of snow and ice is increasingly being dimmed by air pollution.

From Greenland's ice sheets to Himalayan glaciers and the snowpacks of western North America, layers of dust and soot are darkening the color of glaciers and snowpacks, causing them to absorb more solar heat and melt more quickly, and earlier in spring.

This trend toward darker snow from soot and dirt has been observed for years. Sources vary from dust blowing off deserts and snow-free Arctic land, to soot from power plants, forest fires, and wood-burning stoves. But now soot and dust are taking a greater toll, according to a report released this week, causing Greenland's ice sheets to darken—and melt—at a faster rate in spring than before 2009.

This matters because Greenland is mostly covered in ice, and meltwater from thawing continental glaciers like those found in Greenland and Antarctica flows into the ocean, causing seas to rise. Greenland, the world's largest island, holds enough ice that if it all melted seas would rise—likely over centuries—up to 20 feet.

Connecting Dots: The News in Perspective

This darkening of Greenland ice by soot and dirt will probably cause seas to rise faster toward the end of this century than previously forecast. (Reports last month indicated portions of the Antarctic ice sheet were also melting faster than forecast.)

Photo of melting snow containing light absorbing impurities.
The springtime darkening of the Greenland ice sheet since 2009 may be attributable to an increase in the amount of impurities—such as soot—in snow.
Photograph by Florent Dominé

Whiteness and Melting

Albedo, or "whiteness," is a scientific term meaning reflectivity. It is the fraction of solar energy that Earth reflects back into space. Lighter colored areas of Earth—those covered in new snow and ice—reflect most solar energy back into space. Darker areas of Earth—oceans, forests, and cities—absorb more solar heat.

This whiteness is why snow-covered areas can stay cold, while dark spots like pavement and black roofs heat up. So when the white color of snow and ice is darkened by dirt and soot, more of the sun's heat is absorbed, and snow and ice melt faster.

Researchers have also attributed some Arctic ice cap melting to darkening from soot. Further, as Arctic Ocean ice thaws in spring and summer, more adjacent dark, heat-absorbing water is exposed. This dark water is warmed by the sun's rays, and in turn melts even more ice nearby. In what scientists call a "feedback loop," melting causes even more melting, more heat-absorbing dark water is exposed as more ice melts, and even more ice melts because more dark water is exposed, and so on.

Satellite images in 1979 first revealed the size of the Arctic ice cap, and since then Arctic ice has retreated about 12 percent per decade in summer. This is a trend that has accelerated since 2007, driven primarily by rising global temperatures. In September 2012 nearly half the ice cap melted in summer, leaving a record low amount of ice, and in May 2014 Arctic sea ice extent was third lowest on record.

Showing this dramatic Arctic ice loss is one of the most striking changes in the National Geographic atlas's long history, according to National Geographic Geographer Juan José Valdés, who calls it the map's "biggest visible change other than the breakup of the U.S.S.R."

Photo of a family sitting around a cooking stove.
An acrid haze hangs over a family sitting around a cooking stove in Qinghai Province in China.
PHOTOGRAPH BY JONAS BENDIKSEN, NATIONAL GEOGRAPHIC CREATIVE

Dirt Darkening Mountain Snow

It's not just Greenland and Arctic ice caps being affected by soot and dust. Atmospheric dirt is changing Himalayan glaciers in Asia and snowpacks in the mountains of western North America.

Studies show cooking stoves that burn dung and wood darken snowpacks and ice in the Tibetan Plateau of the Himalayas. Soot from these biomass stoves falls on and darkens snow and ice in this region, whose extensive glaciers give birth to Asia's largest rivers—the Yangtze, Yellow, Mekong, and Ganges—and provide water for two billion people.

A 2009 study in the Proceedings of the National Academy of Sciences documented how soot is playing a role in the retreat of Himalayan glaciers. Efforts are under way to produce cleaner-burning cookstoves that reduce pollution and improve the health of people who rely on them.

Wind storms that carry dirt off the deserts of the U.S. Southwest are darkening the snowpacks of the Colorado Rockies with layers of red dust, causing snow to melt up to six weeks earlier than in the 1880s. This early snowmelt causes streams to swell earlier in spring before plants are ready to use the water, and streams run low later in the year when the water is most needed for drinking and irrigation.

But western snowpacks aren't suffering from just dust and dirt. Rising temperatures and lack of snow this winter in the Sierras and the Cascade Range signal an emerging "new normal" in the western United States. On May 1, when researchers traveled to high mountain sites in the Sierras to measure snowpack, there was little snow to measure.

And researchers expect mountain snows to keep shrinking. This week in early June, no snow remains at measuring locations in the Sierras, according to California's Department of Water Resources.

We can expect these trends to continue. A May 2014 study in the Proceedings of the National Academy of Sciences reported a link between black carbon from northern boreal forest fires and faster melting in 2012 of the Greenland ice sheet. And a study in 2013 documented that boreal fires in Alaska are burning more frequently now than at any time in the past 10,000 years.

A 2011 U.S. Geological Survey study suggests we will see more dust storms in the U.S. Southwest in years ahead, as continued warming and drying makes survival of shrubs and grasses—plants whose roots help keep soil in place—more difficult. The National Climate Assessment released last month indicates the Southwest will also be more vulnerable to fires.

So it's likely we could be looking forward to more dust, more melting, and a long ride on the global warming feedback loop.

Dennis Dimick is National Geographic's Executive Editor for the Environment. You can follow him on Twitter, Instagram, and flickr.

8 comments
Paul Schott
Paul Schott

AIR POLLUTION FROM OIL AND COAL in large cities around the earth turn white snow in days to a black frosting covered snow. Any one living in Chicago, Illinois  will tell you this.


Burning oil fields by the lost in 1991 did not help Earth's Ice Sheets and Glaciers.



Father is that day of wrath near for them that destroy the Earth?  KJV Rev 11:18

Father look another fish near the top of the water Young Eagle soon there will be many as the water goes down.
Father and when the water is gone what will we eat Young Eagle that is foretold in Revelation 19:17-18
Have no fear young Eagle, those who are faithful to our Father in Heaven to the end will be saved.


Father and the wicked and lost Young Eagle Most of them will die in the desert because they did not believe
and were not faithful as did more then 3,000 years ago.


Satan's Sin City “Las Vegas” very soon to die like a fish out of water.


World Leaders Pay Close "ATTENTION".


This Planet Earth Cannot And Will Not Support Life As We Know It Without Its FOREST.
Soon all will take note to the sounds and rumbling of Volcanoes and Earthquakes Around Earth that are Waking Up at a Alarming Rate.
Just as they did in 1883 from Krakatoa.


LEADERS PLANT TREES WHILE YOU STILL CAN.


Read well and study on your own after you have read this.


This is not a game or joke our Sun gives off a Solar Wind all day year round. If you live in the State of Alaska you see it in the
sky above what a sight it is going through our Earth’s Magnet Polls of the North and the South, North Poll. It’s called the
Northern Lights or the Aurora Borealis. The day will come when you will be able to see it all over Earth as in the year 1859 Solar Flare,
It was the largest in 500 years. Two Astronomer’s Hodgson and Carrington told the World that the Solar Flare made a Geomagnetic
Storm reach Earth in hours not days. Back then it gave new meaning to "Reach For The Skies" from Telegraph Operators.
For hours sparks flew from the key board. Even after the Batteries were disconnected. Nov 3 and 4, 2003 had a X40+ Class Solar Flare,
Thank GOD it was not coming at Earth this time.


Our Sun’s UV Rays will get stronger as each passing day goes by, read and i will tell you why. The Great big FOREST have be stripped
from most of the Earth for Greed of Money by the Wicked. The trees our are Main Source of Oxygen on this Plant. The Forest Trees scrubs
the Pollution out of the air and makes Oxygen from the rain and dirt that it grows in. The Forest Trees do more than just make Oxygen
they stop Soil Erosion, just Look at the 1930 Dust Bowl. Greed by our wicked Government leaders to bleed from us as much money as they
could out of us thru taxes led farmers to clear cut all their Forest, and farm all the land they were being Tax on.
They had to farm it to pay for the Taxes. Why leave the Trees when food crop makes Money.



Beto Sabio
Beto Sabio

Chinese coal soot.....  in Northern Canada, Arctic, and Colorado !

Let U. S. not ignore "4 corners coal electric generating plants" !

Julius Lim
Julius Lim

the day is come and day wil come ….

craig hill
craig hill

The road to self-extinction. Cleansing. 

Gwendolyn Mugliston
Gwendolyn Mugliston

Malthus would cry in horror, shame and anguish.  


And I wonder, is the increase in ice melt linear or exponential?  

KENNETH LANE
KENNETH LANE

Too many people!  What glorious morons we have running planet Earth!

Peter lubrani
Peter lubrani

I wonder if dust and soot from vulcano activities has been included by this article. 

It is also fairly northern based, what is going on in the south of the world?

Jack Wolf
Jack Wolf

@Peter lubrani  You can measure volcano output in millions of tons, but industrial pollution in giga-tons (ie billions of tons).  That should give you an idea of the scale of the difference between the two inputs of soot/dirt. 

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