Reference
Welker, J.M., Fahnestock, J.T., Henry, G.H.R., O'Dea, K.W. and Chimners, R.A. 2004. CO2 exchange in three Canadian high Arctic ecosystems: response to long-term experimental warming. Global change Biology 10: 1981-1995.
What was done
Working near Alexandra Fiord (79°N) on Ellesmere Island, Nunavut, Canada, the authors warmed portions of three tundra ecosystems spanning a soil water gradient (dry, mesic and wet) by merely placing small (1.8 m2 surface area, 50 cm tall) open-top chambers on the ground, which passively warmed summertime air and soil surface temperatures by 1-3°C. After eight full years of this warming treatment, they measured CO2 fluxes from the three types of tundra for a period of two additional years.
What was learned
Averaged over the entire two-year period of measurements, net carbon capture was positive in the dry and wet tundra ecosystems but negative in the mesic ecosystem. At the dry site, the passive experimental warming increased annual carbon capture from 23.2 to 26.0 g CO2-C m-2 year-1, while at the wet site it decreased it from 55.3 to 42.1 g CO2-C m-2 year-1. At the mesic site, on the other hand, where there was a carbon loss on an annual basis, the experimental warming reduced the loss, dropping it from -64.6 to -25.4 g CO2-C m-2 year-1. Averaged over the three soil water treatments, therefore, the experimental warming increased annual carbon capture from 13.9 to 42.7 g CO2-C m-2 year-1, or by approximately 200%. This huge percentage increase was driven by a minor increase in carbon capture at the dry site (12%) and a large reduction in carbon loss at the mesic site (61%), which together far outweighed the moderate decline in carbon capture at the wet site (24%).
What it means
As has also recently been demonstrated by Marchand et al. (2004) to be the case in northeast Greenland, warming tends most generally to increase carbon sequestration by high-Arctic tundra, in contradiction of the climate-alarmist claim that it will transform such ecosystems into huge carbon sources and exacerbate the CO2-induced global warming they claim is occurring. In reality, therefore, nature appears to operate just the opposite of how they say it does in this situation.
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