Background
In a small booklet published nearly two decades ago, Idso (1995) described what he called "the deepening 'breath' of earth's biosphere," whereby the aerial fertilization effect of the ongoing rise in the air's CO2 content was causing (1) more CO2 to be removed from the atmosphere via plant photosynthesis during each succeeding spring and summer in the Northern Hemisphere, which was followed each year by (2) a somewhat smaller increase in the amount of CO2 returned to the atmosphere via plant decomposition processes in the fall and winter.

What was done
In an updated, expanded and much improved analysis of the subject, Graven et al. (2013) present "seasonal CO2 cycles observed by the recent High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) large-scale aircraft campaign (Wofsy, 2011) and regular aircraft profiles over several fixed sites by the National Oceanic and Atmospheric Administration (NOAA) Carbon Cycle Group Aircraft Program from 2009 to 2011 and compare them to observations made 50 years earlier during the International Geophysical Year (IGY) (Keeling, 1968)," which latter observations "were obtained by 160 weather reconnaissance flights above the North Pacific and Arctic Oceans from 1958-1961 along 500 and 700 millibar (mb) pressure surfaces (~6 and 3 km altitude)."

What was learned
The fourteen researchers report that this comparison revealed "a strikingly large (~50%) [CO2] amplitude increase north of 45°N, indicating that major ecological changes must have occurred in northern land ecosystems over the past 50 years." And in exploring the subject further, they concluded that the large increase in CO2 amplitude north of 45°N must "be attributed almost entirely to the terrestrial biosphere." Thus, to explore potential mechanisms for the large increase in net primary production (NEP) implied by their findings, they turned to a subset of terrestrial ecosystem models that are currently participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to see what light they could shed on their findings. And what did they find? They found that "none of the CMIP5 models can account for the increase in CO2 amplitude north of 45°N at 500 mb between 1958 to 1961 and 2009 to 2011."

What it means
Graven et al. conclude their paper by stating that "the inability of the CMIP5 models to account for the observed increase in the amplitude of atmospheric CO2 indicates that they underestimate the widespread ecological changes that occurred over the past 50 years and are likely to under-predict future changes."

References
Graven, H.D., Keeling, R.F., Piper, S.C., Patra, P.K., Stephens, B.B., Wofsy, S.C., Welp, L.R., Sweeney, C., Tans, P.P., Kelley, J.J., Daube, B.C., Kort, E.A., Santoni, G.W. and Bent, J.D. 2013. Enhanced seasonal exchange of CO2 by northern ecosystems since 1960. Science 341: 1085-1089.

Idso, S.B. 1995. CO2 and the Biosphere: The Incredible legacy of the Industrial Revolution. Kuehnast Lecture Series Special Publication. Department of Soil, Water and Climate, University of Minnesota, St. Paul, Minnesota, USA, 62 pp.

Keeling, C.D., Harris, T.B. and Wilkins, E.M. 1968. Concentration of atmospheric carbon dioxide at 500 and 700 millibars. Journal of Geophysical Research 73: 4511-4528.

Wofsy, S.C. 2011. HIPPO Team and Cooperating Modelers and Satellite Teams. Philosophical Transactions of the Royal Society A 369: 2073-2086.