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Another subarctic positive feedback - Oh for peat's sake!

post #1 of 11
7/29/09 at 12:34pm
Thread Starter 
From Nature, latest issue ...

Carbon respiration from subsurface peat accelerated by climate warming in the subarctic

pp616-619

The feedback between the terrestrial carbon cycle and climate is one of the largest uncertainties in current projections of future climate, with the long-term sensitivity of carbon in peatlands remaining unclear. The combination of non-disturbing in situ measurements of carbon dioxide respiration rates and isotopic composition of respired CO2 in subarctic peatland experiments now shows that warming accelerates espiration rates of these subsurface carbon reservoirs to a much larger extent than was previously thought.
Ellen Dorrepaal et al.

doi:10.1038/nature08216

Abstract:

Article:
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post #2 of 11
7/29/09 at 12:55pm
Quote:
we estimate that climate warming of about 1 °C over the next few decades could induce a global increase in heterotrophic respiration of 38–100 megatonnes of C per year.

That's not too too bad. Humans emit 26.4 Gt / year right? So this feedback is only like 0.4 % of what humans emit, at most?
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post #3 of 11
7/29/09 at 12:56pm
I read another study on this subject about a year ago.

Quote:
In our long-term simulation, an experimental warming of 4°C causes a 40% loss of soil organic carbon from the shallow peat and 86% from the deep peat. We conclude that peatlands will quickly respond to the expected warming in this century by losing labile soil organic carbon during dry periods."

Peatland also tends to release its carbon as methane, which makes it an even bigger feedback.
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post #4 of 11
7/29/09 at 1:06pm
Quote:
Originally Posted by dawei View Post



That's not too too bad. Humans emit 26.4 Gt / year right? So this feedback is only like 0.4 % of what humans emit, at most?
 


No, that's human CO2 emissions.  Human carbon emissions are about 7 Gt/year.  So it's closer to 1%.  However, if it were all released as methane, then you're talking closer to 20% global warming contribution.  And that's just for a 1°C warming.
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post #5 of 11
7/29/09 at 2:01pm
Quote:
Originally Posted by dana1981 View Post
No, that's human CO2 emissions.  Human carbon emissions are about 7 Gt/year. 

Oops, that's right.

How much of that carbon do you reckon would be released as methane? The article treats it as if it would all be CO2.
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post #6 of 11
7/29/09 at 2:21pm
It looks like maybe 20%.

Quote:
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post #7 of 11
7/30/09 at 11:55am
Thread Starter 
The interesting thing is that nearly all of the feedbacks identified are positive, none are negative.  This suggests climate is more sensitive to increases in CO2 that predicted by models, which is what the empirical observations also show. 

I don't think we will have to wait much longer before skeptics will have to stop claiming there has been cooling since 1998. 
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post #8 of 11
7/30/09 at 12:48pm
Yeah this is why the Spencer-style claims of low climate sensitivity seem so implausible.  Besides the fact that they would make past major climate changes pretty darn hard to explain, the only significant potential negative feedback I've seen identified is low cloudcover, which may even be a positive feedback too.  On the positive side you've got decreasing albedo (melting ice), CO2 from oceans and the biosphere, methane from tundra/melting permafrost and warming peat, increasing atmospheric water vapor, and so on (I'm sure I'm forgetting several).  To suggest that the cloud feeback which may or may not even be negative to begin with will compensate for all these major positive feedbacks just seems ludicrous to me.
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post #9 of 11
8/5/09 at 4:08pm
i have been worried about this for a few years now, since i did my dissertation on peat bogs. bare peat will degrade rapidly, loosing carbon in four ways; anaerobic decomposition in mires and fens producing methane, organic carbon released into watercourses, aerobic decomposition into co2 in dryer parts, and lastly peat fires.
there is 15 000 years worth of peat built up in siberia and canada, which is being exposed by rapidly melting permafrost

something was obviously amplifying the temperature swings during the last ice age, ocean current patterns seem to be the best bet fr starting them, but i am convinced that movement of carbon in and out of peat sinks is a major positive feedback.
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post #10 of 11
8/6/09 at 2:36pm
Peat has another positive feedback.  The bacteria breaking it down generate heat that will accelerate the decomposition process.  My students measured an average 6 C difference between water in a sewage lagoon and the ambient air temperature this spring and summer.  This difference was also measured in an indoor scale model apparatus in the lab.  While the composition is a bit different, there is a lot more organic material per cm^3 in the peat and hence a potential for more than 6 C heating once the microbes get working.  In the sewage lagoon, zoo plankton act as a negative feedback by limiting the bacteria population.
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post #11 of 11
8/14/09 at 2:27pm
ooh errrr..... that makes the enzymatic latch process even more scary, as it is also temperature dependant (and also increases with higher nitrogen and co2 levels).....
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