What was done
The authors examined the effects of temperature and land disturbance on carbon exchange in an effort to determine which of these two factors could better explain the increasing amplitude of the seasonal CO2 cycle that has been occurring in the mid to upper northern latitudes in recent decades.  To accomplish their objective, the authors measured the seasonal amplitude of carbon exchange for three years at five natural or undisturbed sites and at five disturbed sites in northeast Siberia.

What was learned
The seasonal amplitude of CO2 exchange, calculated as the difference between summer uptake and winter efflux, was found to be 2.3 to 3.6 times greater at disturbed locations as opposed to undisturbed ones.  Interannual temperature differences, as well as temperature differences arising from different site locations, appeared to have little or no effect on the seasonal exchange of CO2.

What it means
According to the authors, if the fluxes they observed are representative of the whole upper latitudes, "disturbance would have increased the seasonal amplitude of high-latitude carbon flux by about 15% since the 1960s."  Such a value represents from one-third to three-fourths of the amplitude increase that has been observed in the seasonal cycle of the air's CO2 content in the mid to upper latitudes since the 1960s.  If correct, the results of this study cast further doubt on the claim that global warming is responsible for the reported amplitude increase, a claim that we have also examined in our Journal Review The Increasing Amplitude of the Atmosphere's Seasonal CO2 Cycle: A Minimal Role for Global Warming.