A new modeling study from NASA confirms that when tiny air pollution particles we commonly call soot – also known as black carbon – travel along wind currents from densely populated south Asian cities and accumulate over a climate hotspot called the Tibetan Plateau, the result may be anything but inconsequential.
In fact, the new research, by NASA’s William Lau and collaborators, reinforces with detailed numerical analysis what earlier studies suggest: that soot and dust contribute as much (or more) to atmospheric warming in the Himalayas as greenhouse gases. This warming fuels the melting of glaciers and could threaten fresh water resources in a region that is home to more than a billion people.
Lau explored the causes of rapid melting, which occurs primarily in the western Tibetan Plateau, beginning each year in April and extending through early fall. The brisk melting coincides with the time when concentrations of aerosols like soot and dust transported from places like India and Nepal are most dense in the atmosphere.
“Over areas of the Himalayas, the rate of warming is more than five times faster than warming globally,” said William Lau, head of atmospheric sciences at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Based on the differences it’s not difficult to conclude that greenhouse gases are not the sole agents of change in this region. There’s a localized phenomenon at play.”
He has produced new evidence suggesting that an “elevated heat pump” process is fueling the loss of ice, driven by airborne dust and soot particles absorbing the sun’s heat and warming the local atmosphere and land surface. A related modeling study by Lau and colleagues has been submitted to Environmental Research Letters for publication.
A unique landscape plays supporting actor in the melting drama. The Himalayas, which dominate the plateau region, are the source of meltwater for many of Asia’s most important rivers—the Ganges and Indus in India, the Brahmaputra in Bangladesh, the Salween through China, Thailand and Burma, the Mekong across Laos, Cambodia and Vietnam, and the Yellow and Yangtze rivers in China. When fossil fuels are burned without enough oxygen to complete combustion, one of the byproducts is black carbon, an aerosol that absorbs solar radiation (Most classes of aerosols typically reflect incoming sunlight, causing a cooling effect). Rising populations in Asia, industrial and agricultural burning, and vehicle exhaust have thickened concentrations of black carbon in the air.
Sooty black carbon travels east along wind currents latched to dust – its agent of transport – and become trapped in the air against Himalayan foothills. The particles’ dark color absorbs solar radiation, creating a layer of warm air from the surface that rises to higher altitudes above the mountain ranges to become a major catalyst of glacier and snow melt.
- CLICK TO VIEW ANIMATION – Tiny, dark-colored aerosols — specifically black carbon — travel along wind currents from Asian cities and accumulate over the Tibetan Plateau and Himalayan foothills. Seen here as a light brown mass, these brown clouds of soot absorb sunlight, creating a layer of warm air (seen in orange) that rises to higher altitudes, amplifying the melting of glaciers and snow. Credit: NASA/Sally Bensusen Nicknamed the “Third Pole”, the region in fact holds the third largest amount of stored water on the planet beyond the North and South Poles. But since the early 1960s, the acreage covered by Himalayan glaciers has declined by over 20 percent. Some Himalayan glaciers are melting so rapidly, some scientists postulate, that they may vanish by mid-century if trends persist. Climatologists have generally blamed the build-up of greenhouse gases for the retreat, but Lau’s work suggests that may not be the complete story.
Building on work by Veerabhardran Ramanathan of the Scripps Institution of Oceanography, San Diego, Calif., Lau and colleagues conducted modeling experiments that simulated the movement of air masses in the region from 2000 to 2007. They also made detailed numerical analyses of how soot particles and other aerosols absorb heat from the sun.
“Field campaigns with ground observations are already underway with more planned to test Lau’s modeling results,” said Hal Maring who manages the Radiation Sciences program at NASA Headquarters in Washington. “But even at this stage we should be compelled to take notice.”
“Airborne particles have a much shorter atmospheric lifespan than greenhouse gases,” continued Maring. “So reducing particle emissions can have much more rapid impact on warming.”
“The science suggests that we’ve got to better monitor the flue on our ‘rooftop to the world,” said Lau. “We need to add another topic to the climate dialogue.”
h/t to Dr. Roger Pielke Sr.
Related Links:
> The Dark Side of Carbon: Will Black Carbon Siphon Asia’s Drinking Water Away?
> Soot is Key Player in Himalayan Warming, Looming Water Woes in Asia
> Asian Summer Monsoon Stirred by Dust in the Wind
> A Unique Geography — and Soot and Dust — Conspire Against Himalayan Glaciers
Gretchen Cook-Anderson
NASA Earth Science News Team
Having seen that map I’m off to Tibet to harvest that carbon black. You wouldn’t believe what it costs to produce that stuff industrially.
Bill Illis (19:27:56) :
Hang on hang on hang on…
http://data.giss.nasa.gov/modelforce/RadF.gif
That says that land use is a negative forcing? I can’t think of a single land use activity over the 20th century (new roads, deforestation, concrete… maybe damns?) that would result in a negative forcing. Am I missing something here?
Nick B. (08:24:53)
Land-use is a negative because deforestation and agricultural land acts to increase Albedo. (Technically, this forcing also includes the Urban Heat Island so it is a little counter-intuitive). Deforestation out-weighs the growth of the cities I guess. Its just that most of the temperature stations are in the cities and not in the rural areas.
Bill,
Interesting… for some reason I guess I had gotten the impression that deforestation would increase temperatures… I guess that was really pointing to the indirect effect through CO2 (since everything’s caused by CO2 amirite?)
Damn forests… warming up our globals and what not 😉
Thanks for the reply good sir!
Will someone help a layman out?
I’ve been up the side of Pumori, a mountain very close to Everest and Nuptse, separated from them by the great Khumbu glacier. There’s very little air up there ( roughly 18,400 ft): sound carries poorly, and one’s judgment of distance is messed with, as EVERYTHING looks wonderfully crystal clear and up-close, due to the lack of air and water vapor.
So I am wondering….
Unlike most glaciers in, say, Alaska and Greenland, those in the Himalayas are at high altitudes, where the entire atmosphere is very thin. CO2, we have learned, is a relatively heavy molecule (at least vs O2 and N2), and would thus have a tendency to sink in any atmospheric column.
So… thin atmosphere, and a smaller fraction of CO2 in that high-altitude atmosphere than one would find at lower altitudes. Right? So…how could CO2 concentrations be the culprit in the slow shrinking of Himalayan glaciers?
The greatest problem highlighted by the CRU emails is the way dissent was stamped upon. Inevitably this prevented alternative global warming hypotheses being explored.
So far I can think of three:
Black carbon. I see no explanation of the isotope changes which can be attributed to this.
The Kreigesmarine Effect: does the lot including the WWII blip.
The Silicate Hypothesis: dissolved silicate increases the diatom bloom at the expense of coccolithophores. Heavy carbon pulldown is relatively increased while overall CO2 pulldown is decreased. DMS production is reduced so fewer low level clouds, more heating. I like this one — which I thought of last night — because it also does the cod population collapse on the Grand Banks.
Oh, no, make that four. A trace gas which encourages cloud formation somehow uses the clouds to increase its tiny greenhouse effect. Depending as it does on the idea that up to the production of anthropogenic CO2 the system was in a position of exquisite balance, a balance which was unable to take the tiniest disturbance, this one is an obvious non-starter.
Can you imagine how difficult it would have been to obtain funding to investigate 1,2,3 in the last twenty years?
JF