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The Effect of Warming on the Carbon Balance of High-Arctic Tundra
Reference
Marchand, F.L., Nijs, I., de Boeck, H.J., Kockelbergh, F., Mertens, S. and Beyens, L.  2004.  Increased turnover but little change in the carbon balance of high-Arctic tundra exposed to whole growing season warming.  Arctic, Antarctic, and Alpine Research 36: 298-307.

What was done
The authors determined the carbon balance of tundra vegetation over the snow-free season in northeast Greenland (74N, 21W) via measurements of gross photosynthesis, belowground (root) respiration and canopy respiration in plots exposed to either ambient environmental conditions or to conditions similar in all respects except temperature, which was maintained 2.5C above ambient by infrared radiation emitted by two 1500-W heaters placed on tripods positioned just to the north of each plot ("dummies" were used in the case of control plots) to minimize blockage of incoming solar radiation.

What was learned
Under the warmer conditions studied, gross photosynthesis was enhanced by 24%, while soil respiration was enhanced by 33% and canopy respiration by a smaller insignificant amount.  Nevertheless, because absolute rates of gross photosynthesis were about twice as large as root respiration rates, the net carbon balance of the tundra was increased by the warming, rising from an ambient value of 0.86 mol CO2 m-2 to a warming-induced value of 1.24 mol CO2 m-2.  Consequently, the strength of the summer tundra carbon sink rose by fully 44% in response to the 2.5C increase in temperature.

What it means
Because there was already so much carbon in the soil, the small addition produced by the warming of the environment would have been next to impossible to detect for many years.  Nevertheless, over long time periods, it all adds up.  In addition, the warming-induced increase in the tundra carbon sink must be viewed in the light of prior warnings that global warming would transform it into a carbon source (Mitchell et al., 1990), thereby exacerbating global warming via a positive feedback cycle.  The new finding, at least in this case, sets the issue to rest.  For more on this subject, see the various materials we have archived under Carbon Sequestration (Temperature Effects) in our Subject Index, which set the issue to rest even further.

Reference
Mitchell, J.F.B., Manabe, S., Meleshko, V. and Tkioka, T.  1990.  Equilibrium climate change.  In: Houghton, J.T., Jenkins, G. and Ephraums, J.J., Eds. Climate Change: The IPCC Scientific Assessment.  Cambridge University Press, Cambridge, UK, pp. 131-172.

Reviewed 11 May 2005