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.”

17 thoughts on “Alaska warming from Arctic tundra shrub invasion and soot deposition?

  1. 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?

  2. 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.

    John

  3. 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?

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  5. Pingback: Shrubs & Soot - Not Bush & Suits « Waste Of My Oxygen

  6. BCL, thank you for your comment but I think you’ve missed the point. It’s a regional, not a global effect. I assume you were referring to this passage: “Since there has already been pronounced warming at high latitudes and future warming is expected to be most extreme in these
    regions, it is of utmost importance to develop a thorough understanding of the processes governing Arctic climate.”

    But right above that there is this:

    “Soot deposition in the Arctic has the potential to increase in future years owing to increased human activity (energy extraction and ocean shipping) in the region [Hansen and Nazarenko, 2004]. Soot lowers the albedo of the snowpack, leading to enhanced absorption of solar radiation.”

    What Pielke is suggesting is that shrubs can be the secondary regional effect of the soot. The soot deposition is the catalyst. The two together make a strong positive feedback. Though Pielke didn’t touch on it, there may also be a biological driver for the shrubs, due to changes in the regional biosphere, which could be anthropogenic in the source. Increased human populations in areas often have tag along species that follow. I’d wager that there are more humans near tundra now than 100 years ago.

    Unfortunately, I think you see what you want to see in this case, like in your recent posts on Bigfoot pictures on your own website.

    BCL, why not go chase some Bigfoot on the tundra as you’ve devolved into doing on your own blog lately? I’ll bet they are hiding behind the shrubs. “Bigfoot City Lib” has a nice ring to it, work it for some more radio time, it fits you well.

  7. 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?

  8. Well I’ll ask Pielke himself and see what his intent was.

    BCL, I’m not at all fond of your Bigfoot entries, don’t put words in my mouth.

    And as for surfacestations.org that’s all for me to know and you to find out. Since you are hostile to the project, I don’t feel inclined to give you the latest update early.

    I never made any claims about NASA nor did anything beyond census tabulations of the results. Some others took preliminary data and drew some conclusions, others took the same data and drew other conclusions. You only like to draw attention to the former, again seeing what you want to see.

    I’ve drawn no conclusions yet from the data beyond the census tabulations. Again, don’t put words in my mouth.

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

  10. 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.

  11. Pielke has responded that he will write a clarification of his work related to how he viewed the regional warming issue.

    I’ll post it as soon as he provides it.

  12. 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
    http://climatesci.colorado.edu/2007/06/19/a-new-paper-that-highlights-the-first-order-radiative-forcing-of-black-carbon-deposition/ and on the relative fraction of global warming from the radiative effect of CO2, in which soot is included [http://climatesci.colorado.edu/2006/04/27/what-fraction-of-global-warming-is-due-to-the-radiative-forcing-of-increased-atmospheric-concentrations-of-co2/].

  13. Pingback: Climate Science: Roger Pielke Sr. Research Group News » Arctic Tundra Shrub Invasion And Soot Deposition: Consequences For Spring Snowmelt And Near-surface Air Temperatures

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