Observational constraints of the past CO2 concentration on the results of carbon cycle models

A paper by Zecca and Chiari has followed the work of Nel and Cooper (both in Energy Policy), dealing with the same issue of evaluating the future atmospheric CO2 concentration under the constraints imposed by fossil-fuels depletion. The two papers suggest the need of revising the IPCC SRES emission scenarios. In this number, further works by Ward and Nel and by Zecca and Chiari aim at improving the outcomes of the carbon cycle models used for the calculation of the CO2 concentration starting from the emission values. Here, methodological differences between the two groups are discussed.