Alaska warming from Arctic tundra shrub invasion and soot deposition?

Dr. Roger Pielke forwarded me his latest paper published in the JOURNAL OF GEOPHYSICAL RESEARCH, for release. It has quite a different take on the issue of regional warming in Alaska. Given the emotional testimony given in congress this week by Cheryl Charlee Lockwood, who is a recent high school graduate and works in the Alaska Youth for Environmental Action program, before the House Select Committee on Energy Independence and Global Warming, this study seemed relevant to current events.

From the abstract:

“Invasive shrubs and soot pollution both have the potential to alter the surface energy balance and timing of snow melt in the Arctic. Shrubs reduce the amount of snow lost to sublimation on the tundra during the winter leading to a deeper end-of-winter snowpack. The shrubs also enhance the absorption of energy by the snowpack during the melt season by converting incoming solar radiation to longwave radiation and sensible heat. Soot deposition lowers the albedo of the snow, allowing it to more effectively absorb incoming solar radiation and thus melt faster.”

“The results of the simulations suggest that a complete invasion of the tundra by shrubs leads to a 2.2°C warming of 3 m air temperatures and a 108 m increase in boundary layer depth during the melt period. The snow-free date also occurred 11 d earlier despite having a larger initial snowpack. The results also show that a decrease in the snow albedo of 0.1, owing to soot pollution, caused the snow-free date to occur 5 d earlier. The soot pollution caused a 1.0°C warming of 3 m air temperatures.”

The entire paper can be viewed here (PDF file) There is some precededence for the soot theory, as seen in this 2003 NASA News Release where they say “…black soot may be responsible for 25 percent of observed global warming over the past century.”

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November 6, 2007 6:27 pm

Shrubs are a positive feedback. That should make the warmingistas happy.

November 7, 2007 6:51 am

So when the IPCC said that they were 90% certain that AGW was caused by CO2, what percentage of AGW did they attribute to soot?

John Dittes
November 7, 2007 12:00 pm

Yet another warming feedback added to the already long and growing list. Don’t confuse it with a “chicken or egg” situation though. As the author probably clarifies, the latitude and elevation limits of woody species are generally determined by low temperatures/short growing seasons. Shrub species advance north because of a warming trend…the advancing shrubs then contribute to the warming trend. The canoe clearly seems to be tipping; doesn’t really seem tp matter how it lost its balance once your going headfirst into the water.

November 7, 2007 12:12 pm

Soot, from China deposited in the Arctic region, is a theory I can actually get behind and believe. It makes MUCH more sense to me. And since the bulk of the warming has actually occured in the Arctic regions (remember how cold the SH was this winter?) that is a more plausible explaination then CO2.
Please correct me, but I think the IPCC has soot as a negative feedback (particles in the atmosphere blocking/reflecting heat) but doesn’t consider soot on the ground. Yes/no?

November 7, 2007 5:01 pm

[…] Alaska warming from Arctic tundra shrub invasion and soot deposition? [image] Dr. Roger Pielke forwarded me his latest paper published in the JOURNAL OF GEOPHYSICAL RESEARCH, for release. […] […]

November 8, 2007 4:01 am

How is this a different take when Pielke claims in the 2nd par that the “shrub invasion” is itself caused by warming temperatures?

November 8, 2007 4:42 am

[…] Not Bush & Suits Another horrible nail in the Al Gore Global Warming Scandel… After a recent highschool graduate testitfied for Congress on Global Warming effects in Alaska, we should all be panicing as the devestating effects and soon to be reality of Al Gore’s […]

November 8, 2007 5:40 am

There are several references to warming already occuring in that region throughout the paper, and I see no suggestion that Pielke is postulating a causal chain from increased soot ->increased warming->increased shrub cover-> increased warming. This does NOT seem to be the point of the paper. Or can you point to a passage?
PS. Glad you like the Bigfoot stuff. Whats up with Surface Stations? Everyone go home when you inadvertantly proved NASA’s temperature reconstructions?

Alan D. McIntire
November 8, 2007 7:15 am

I enjoyed seeing a new article by Pielke. I miss his updates on his late “climate science” blog.

November 9, 2007 1:06 am

If shrubs are a positive feedback, then anthropomorphic vegetation (loss or gain) is a primary driver of climate.
I also sorely miss Pielke’s site. He got the land use change causing local/regional climate change connection.

Earle Williams
November 9, 2007 2:02 pm

Landscape-scale changes in arctic vegetation have been reported as being primarily due to changes in precipitation. See Mann et al, 2002 (not that Mann!)

Earle Williams
November 9, 2007 2:03 pm

Correction – the referenced paper refers to moisture, not precipitation.

November 11, 2007 6:37 am

Thank you for the comments on our paper. With respect to why the shrubs have increased in coverage, this issue needs further investigation. We did not discuss this in our paper, but focused on how once they are present, shrubs and soot affect the melt in the spring, and resultant effects on the surface energy budget.
The role of soot as a warming climate forcing in the Arctic is becoming better recognized, and our paper looks at this issue on a regional scale. On why there is added soot, this is clearly from anthropogenic emissions and long range transport from the source regions.
On why there are more shrubs, changes in temperatures (particularly daytime growing season), increase in the atmospheric concentration of CO2 (which could result in a biogeochemical boost for the shrubs, more than other tundra vegetation), and/or changes in precipitation are candidates.
Regardless, we show that soot and shrubs can both be warming influences, which thus reduces the relative contribution of the radiative effect of CO2 to such warming. See also my discussion on Climate Science on soot and on the relative fraction of global warming from the radiative effect of CO2, in which soot is included [].

November 27, 2007 3:16 pm

[…] paper has aleady been discussed on Watts Up With That but I want to further emphasize that this research demonstrates not only the role of shrubs on […]

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