April 5, 2005

Is soot, not CO2, to blame for the loss of Arctic ice?

There are three primary tools that global warming alarmists use in their arguments that anthropogenic enhancements to the world’s naturally occurring greenhouse effect are causing the climate to behave as it never has before and this will ultimately be catastrophic. They are 1) the “hockey stick” temperature reconstruction for the past 1,000 years, which purports to show that left to its own devices, the global average temperature changes very little, yet it jumps at the slightest provocation from mankind; 2) the IPCC 21st century temperature projections which show a range of possible warming by century’s end that spans 1.4 to 5.8ºC (of course, the alarmist attention is given to the high end projection); and 3) the sea ice in the Arctic Ocean has been steadily declining for the past several decades and will be entirely gone in the summertime in the next 50 years as a result of rising levels of atmospheric greenhouse gases. With the latest publication by NASA scientists Dorothy Koch and James Hansen, the final of these arguments now joins the first two in being soundly repudiated.

The first one, the “hockey stick,” has been under relentless attack since it was first proposed in the late 1990s. It was ultimately killed with the publication of the work of Sweden’s Anders Moberg just a month ago. Moberg and colleagues have shown that the true temperature history of the past 1,000 years was likely much more variable than the “hockey stick” reconstruction makes it out to be, with a sizable warm signal during the Medieval Warm Period about 1,000 years ago, followed by a substantial cooling (The Little Ice Age) bottoming out in the 1800s. Consequently temperature changes observed during the early and late 20th century don’t look so unusual in the historic record. We documented the death of the “hockey stick” in detail in an earlier posting (see http://www.worldclimatereport.com/index.php/2005/03/03/hockey-stick-1998-2005-rip/).

The second notion, that the high-end temperature projections issued in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) are even plausible has been dead for a while. This was killed by a collection of articles which showed that observed climate changes—changes which wholly integrate all physical processes (unlike global climate models)—indicate that the most likely future pathway taken by global temperatures will be one that lies very near the low end of the IPCC warming rate projections, or about 0.15ºC or so per decade. We detail these results also in an earlier posting (see http://www.worldclimatereport.com/index.php/2004/04/14/observations-not-models/).

And now comes a severe blow to the third argument—that anthropogenic changes to the greenhouse effect, resulting from the burning of fossil fuels, are leading to the rapid loss of Arctic ice. Instead, Koch and Hansen, writing in the Journal of Geophysical Research, document that the impact of black carbon (soot) pollution on the Arctic climate is quite likely the primary driver of Artic temperature increases and sea ice declines during the past several decades. Soot is an entirely different beast than carbon dioxide, in that it is a particulate that remains only in the atmosphere for a short time, and which can be relatively easily removed from smokestack emissions. In fact, most first-world countries have programs aimed at reducing air pollution that include soot reduction measures.

Koch and Hansen suggest that soot warms the Arctic is two primary ways. When it is suspended in the atmosphere, soot absorbs incoming solar radiation and warms the atmosphere while possibly decreasing cloudiness. On the ground, it blackens the snow and ice, making it less reflective so that it absorbs more warming radiation.

Where does all of this warming soot that finds its way into the Arctic environment come from? According to Koch and Hansen, primarily from the heavy industry and biomass burning in South Asia and Russia. The current North American contribution is estimated to be only about 10-15 percent.

Since Hansen frequently claims that we take his conclusions out of context, we reproduce below the text of a March 23, 2005 NASA press release (http://www.giss.nasa.gov/research/news/20050323/) discussing the findings of Koch and Hansen:

Soot is normally something you think of at the bottom of your chimney, but it also gets into the air, and scientists have been finding it at the frozen Arctic. Soot gets into the air when fuel, vegetation and firewood are burned. When you watch the smoke and soot drift away from your chimney, you normally wouldn’t think that it would drift to the North Pole and change the ice and snow there.

NASA has been exploring how black carbon or soot affects the Earth’s climate, by using satellite data and computer models that recreate the climate. New findings show that soot may be contributing to changes happening at the North Pole, such as increasing melting of sea ice and snow and warming atmospheric temperatures.

Dorothy Koch of Columbia University, N.Y. and NASA’s Goddard Institute for Space Studies (GISS), New York, and James Hansen of NASA GISS are co-authors of the study that appeared in a recent issue of the Journal of Geophysical Research.

“This research offers additional evidence that black carbon may have a significant warming impact on the Arctic,” Koch said. Warmer temperatures in the Arctic mean melting ice and snow, among other things. These temperature and ice changes also wind up affecting climate patterns around the world.

The Arctic is especially vulnerable to pollution. In recent years the Arctic has significantly warmed, and sea-ice cover and glaciers have diminished. Likely causes for these trends include changing weather patterns and the effects of pollution. Airborne soot also warms the air and affects weather patterns and clouds.

Black carbon has already been implicated as playing a role in melting ice and snow. Basically, when soot falls on ice, it darkens the surface and accelerates melting by absorbing more sunlight than ice would, just as wearing a black shirt in the summertime makes you feel hotter than if you wore a lighter color. Dark colors absorb heat and light, and lighter colors reflect it keeping surfaces cooler.

Koch and Hansen used a NASA computer model and information gathered by many NASA satellites to get their finding.

The research found that in the atmosphere over the Arctic, about one-third of the soot comes from South Asia, one-third from burning biomass or vegetation around the world, and the remainder from Russia, Europe and North America.

South Asia is estimated to have the largest industrial soot emissions in the world, and the meteorology in that region readily sweeps pollution into the upper atmosphere where it is easily transported to the North Pole. Meanwhile, the pollution from Europe and Russia travels closer to the surface.

During the early 1980s the main sources of Arctic pollution are believed to have been from Russia and Europe. Both of those areas have decreased their tiny particles of pollution in the last 20 years, but the pollution from South Asia has increased. Koch and Hansen suggest that Southern Asia also makes the greatest contribution to soot deposited on Greenland.

By exploring processes in the Earth’s atmosphere, NASA scientists are seeking answers to how pollutants like soot are changing the climate of the world around us.

In their paper, Koch and Hansen offer up more on the impact of soot vs. an enhanced greenhouse effect. They argue that the temporal and spatial patterns of temperature changes and sea ice declines bear a greater resemblance to patterns of historical soot emissions than to carbon dioxide emissions. Here is what they have to say:

According to the 2002 AMAP [Arctic Monitoring and Assessment Program] Assessment (MacDonald et al., 2003), the past three decades show significant decreases in sea ice thickness and extent. This recent decrease is greatest in spring and fall and occurs in the western Arctic (western North America and Siberia). These observations defy recent modeling efforts, which show the largest impact of increased CO2 on the Arctic winter rather than summer (MacDonald et al., 2003). The pattern of sea ice loss is believed to be linked to the phase of the AO [Arctic Oscillation] (MacDonald et al., 2003). However it is interesting that these decades correspond to the increases in BC [black carbon, soot] from south Asia, and that this BC is transported over the Pacific and into the western Arctic, during summer as well as spring. Prior to this, sea ice also decreased during the 1930s–1940s. However this occurred during winter in the eastern part of the Arctic. Again it is interesting to note that during this earlier period, pollution from coal burning in the United States, Europe and Russia (Novakov et al., 2003) would have been transported to the Arctic during winter-spring, and the Eurasian sources would deposit heavily in the eastern Arctic.

Clearly, Koch and Hansen believe that black carbon soot is a major contributor to the observed Arctic warming as well as to the sea ice decline there. That soot emissions are much more readily controlled than carbon dioxide emissions argues that the most effective strategies in slowing Arctic climate change is through control of black carbon. In the U.S. and in many other technologically advanced countries, air pollution measures targeting soot are already in place, and more are being proposed. According to Koch and Hansen, the culprits lie in the less technologically-developed countries.

The conclusions of Koch and Hansen stand in stark contrast to the tone of the recently released Arctic Assessment Report and of the November 16th, 2004 Senate Hearing held by Arizona Senator John McCain. Both push the idea the primary responsibility for warming in the Arctic lies with the first world emissions of greenhouse gases. During the hearing John McCain uttered words of disbelief and disgust that anyone would dare contend something other than what was written in the Arctic Assessment Report. After the hearing, we compiled a list of scientists and their publications who have characterized the recent climate events in the Arctic in a different manner than that of the Arctic Climate Report (see http://www.worldclimatereport.com/index.php/2004/12/10/open-letter-to-senator-mccain/). We’ll be sure to add Dorothy Koch and James Hansen to that expanding list.


Arctic Climate Assessment (ACIA), 2004. Impacts of a warming Arctic. Cambridge University Press, Cambridge, UK, pp139.

Koch, D., and J. Hansen 2005. Distant origins of Arctic black carbon: A Goddard Institute for Space Studies ModelE experiment. Journal of Geophysical Research, 110, D04204, doi:10.1029/2004JD005296.

MacDonald, R., et al., 2003. AMAP Assessment 2002: The influence of global change on contaminant pathways to, within, and from the Arctic. Arctic Monitoring and Assessment Program, Oslo, 65pp.

Moberg, A., et al., 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433, 613-617.

Novakov, T., et al., 2003. Large historical changes to fossil-fuel black carbon aerosols. Geophysical Research Letters, 30, 1324, doi:10.1029/2002GL016345.

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