The Best Way to Stop the Melting of Arctic Ice and Himalyan Glaciers: Reduce Soot

“The Only Way to Significantly Slow Arctic Warming Over the Next Two Decades”

Preface: Climate activists and skeptics can agree on 6 things. This is one of them.

Professor Mark Jacobson – director of Stanford’s Atmosphere and Energy Program and professor of civil and environmental engineering – says that soot is the primary cause of melting arctic ice:

Soot from diesel engines, coal-fired power plants and burning wood is a bigger cause of global warming than previously thought, and is the major cause of the rapid melting of the Arctic’s sea ice, Stanford climate experts say.


Black and brown carbon in soot [are] an even more powerful contributor to global warming than industrial emissions of methane, which until now have been considered the second most important cause of climate change, Jacobson said.

And because soot absorbs sunlight as it falls on ice and snow and radiates back to Earth from clouds and layers of the atmosphere, it is the major reason for rapidly melting sea ice in the Arctic region, he said.

Controlling soot may be the only way to significantly slow Arctic warming over the next two decades, Jacobson said.


Controlling the soot created by burning fossil fuels, like oil and coal, and from burning wood and dung “may help to reduce Arctic ice loss and global warming faster than any other control option available,” Jacobson concluded.

Indeed, the ability of soot to melt snow and ice is so well-known that, in the 1970s, scientists – including Obama’s top science adviser – proposed pouring soot over the arctic to melt the ice and so prevent the ice age which scientists feared.

We’ve previously noted that soot has been discovered to be a leading cause of snow and ice melting in the Arctic and the Himalayas, soot has a much faster influence on temperature than CO2, and that it is relatively easy to reduce soot.

Time Magazine wrote in 2009:

Black carbon [another name for “soot”] in the air actually absorbs sunlight as it comes from space, directly heating up the atmosphere. “The soot particles are like the parts of a blanket, and it’s getting thicker,” says Ramanathan. “The smoke absorbs sunlight and heats the blanket directly.”

The world’s leading crusader against global warming – Dr. James Hansen – said in 2003:

Soot in snow and ice, by itself in an 1880-2000 simulation, accounted for 25 percent of observed global warming.

NASA wrote in 2005, based on Hansen’s work:

Soot Affects Polar Ice

Posted March 26, 2005

black carbon Any Climate Treaty Which Does Not Dramatically Reduce Soot Is Not Worth the Paper Its Written On
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Far in the frigid north, glaciers rule and temperatures are harsh. It is not the sort of place one would expect pollution to be a problem, but new NASA research reveals that soot is traveling farther north than previously believed. Soot, or black carbon, could have a huge impact on the delicate Arctic environment by speeding up the melting of Arctic ice, altering temperatures and cloud formation, and changing weather patterns.

Black carbon is released into the atmosphere when fossil fuels are not completely burned, either in vehicles, home heating appliances, or when trees and other plants are burned. When large quantities of soot enter the atmosphere, they create a haze that absorbs energy from the Sun, so the temperature of the atmosphere increases. This atmospheric heating can affect weather patterns and cloud formation.

Dorothy Koch and James Hansen, climate scientists at NASA’s Goddard Institute for Space Studies (GISS), modeled the transport of black carbon particles around the world using the GISS general circulation model. The above images show some of their results. The top image shows where black carbon is concentrated in the atmosphere, and thus where surface temperatures and weather patterns might be affected, and the lower image shows where carbon is predicted to settle on the ground.

In the top image, the regions with the most haze—higher optical thickness—are white, while the least-affected areas are blue. As the image shows, Koch and Hansen found that soot in the atmosphere is most concentrated over southern and eastern China, where industry pumps black carbon into the atmosphere, and over central Africa, where fires are widely used for agriculture. Other regions with high concentrations of black carbon include the United States, Central Europe, and India. The model also reveals that instead of being clear of soot, the Arctic is blanketed with black carbon haze. About one-third of the haze, Koch and Hansen say, comes from Asia, one-third comes from fire around the world, and the remaining third comes from the United States, Russia, and Europe.

Soot does not stay in the atmosphere; it falls out in rain or with dust. Koch and Hansen’s research reveals that soot might have a longer range than previously believed, with higher concentrations reaching far into the Arctic. As dark soot falls on the snow and ice of the Arctic, it turns the white, reflective surface into a dark surface that absorbs the Sun’s energy. This extra energy makes the snow melt more quickly.

Studies by other mainstream scientists also demonstrate that much of the melting of Himalyan glaciers is due to soot:

Soot emitted when fuels like diesel, wood and coal are burned, may have a bigger impact on climate in some areas than greenhouse gases. New research presented here at the American Geophysical Union meeting shows that the 20 percent decrease in the extent of Himalayan glaciers since the 1960s may be partly due to an influx of black carbon [i.e. soot] from Asian cities.

As NASA writes:

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.

Indeed, some scientists think that the role of soot is much bigger. As an article from 2002 pointed out:

The research, published in this week’s Science, suggests that soot — produced by diesel engines, cooking fires and other sources — could have nearly as much impact on climate change as carbon dioxide, which has long been considered the primary culprit in global warming.

A group of US and Chinese researchers used a global climate model to simulate how black carbon affects weather patterns. They found that soot can influence regional climate by absorbing sunlight, heating the air and affecting rainfall.

Emissions of soot are particularly large in China because cooking and heating are done with wood, cow dung and coal at low temperatures that do not allow for complete combustion.

And an article published in the journal Nature Geosciences (subscription required) concludes “increasing concentrations of black carbon have substantially contributed to rapid Arctic warming during the past three decades”, and that aerosols are responsible for “half or more” of Arctic warming.

Indeed, Dr. Hansen himself now admits:

Black soot is probably responsible for as much as half of the glacial melt.

A paper published by the National Academy of Science in July 2009 notes:

Our ability to predict how global temperatures will change in the future is currently limited by the large uncertainties associated with aerosols. Soot aerosols represent a major research focus as they influence climate by absorbing incoming solar radiation resulting in a highly uncertain warming effect. The uncertainty stems from the fact that the actual amount soot warms our atmosphere strongly depends on the manner and degree in which it is mixed with other species, a property referred to as mixing state. In global models and inferences from atmospheric heating measurements, soot radiative forcing estimates currently differ by a factor of 6, ranging between 0.2–1.2 W/m2, making soot second only to CO2 in terms of global warming potential. This article reports coupled in situ measurements of the size-resolved mixing state, optical properties, and aging timescales for soot particles. Fresh fractal soot particles dominate the measured absorption during peak traffic periods (6–9 AM local time). Immediately after sunrise, soot particles begin to age by developing a coating of secondary species including sulfate, ammonium, organics, nitrate, and water. Based on these direct measurements, the core-shell arrangement results in a maximum absorption enhancement of 1.6× over fresh soot. These atmospheric observations help explain the larger values for soot forcing measured by others and will be used to obtain closure in optical property measurements to reduce one of the largest remaining uncertainties in climate change.

This is a new discovery. As Time notes:

The science is evolving — it’s so new that black carbon wasn’t even listed as a warming agent in the most recent report from the Intergovernmental Panel on Climate Change — but it cannot be ignored.

Soot Has a More Immediate Effect than CO2

The key is that there is a much shorter lag time between soot and temperature that between CO2 and temperature. As Time writes:

Unlike CO2, which can hang around in the atmosphere for centuries — CO2 that was emitted by the first coal-powered train is probably still in the air, warming the planet — black carbon has a relatively brief life span. It remains just a few weeks in the air before it falls to earth. That’s key, because if the world could reduce black carbon emissions soon, it could help blunt warming almost instantly. “You can wait a week or a month and the totals in the atmosphere can be significantly different,” says Eric Wilcox, an atmospheric scientist with NASA. Meanwhile, if we were to vastly reduce new CO2 emissions immediately, the billions of tons that already exist in the atmosphere would keep warming the planet for decades.

As the Institute for Governance & Sustainable Development writes:

Because black carbon only remains in the atmosphere for several days to weeks, reducing it can bring about almost immediate mitigation of warming, whereas decreases in temperature lag reductions in CO2 by 1,000 years or more.

Good News

Time points out that it is relatively easy to reduce soot:

The good news is that while taking CO2 out of our energy cycle has proven very difficult — especially in poorer developing nations — black-carbon emissions should be easier to curb. Reducing deforestation will help — the burning of tropical rain forests is a big contributor to the black-carbon load. Next, diesel filters in cars can be upgraded, and biomass-burning stoves can be exchanged for technology that uses solar power or natural gas. These changes will cost money, but they should be cheaper than decarbonization. And cutting back on black carbon will also pay immediate health dividends, with less air pollution and fewer deaths from respiratory diseases. We might even be able to see the sky in New Delhi again.

Similarly, Dr. Ramanthan notes in a new paper:

A neglected fast-action strategy presented in the paper is reducing black carbon soot, an aerosol produced largely from the incomplete combustion of diesel fuels and biofuels, and from biomass burning. It is now considered to be the second or third largest contributor to climate change.

“If we reduce black carbon emissions worldwide by 50% by fully deploying all available emissions-control technologies, we could delay the warming effects of CO2 by one to two decades and at the same time greatly improve the health of those living in heavily polluted regions,” said Dr. Ramanathan.

The New York Times also notes the cost-effectiveness of reducing soot:

Decreasing black carbon emissions would be a relatively cheap way to significantly rein in global warming — especially in the short term, climate experts say …

For these reasons, any international treaty or domestic law which does not focus on significantly reducing soot is not worth the paper it’s written on.

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