Fluctuations of CO2 in the last 1000 years higher than expected

The quantity of the greenhouse gas CO2 in the atmosphere has strongly fluctuated during the last thousand years. The Netherlands Organisation for Applied Scientific Research (TNO) and the the University of Utrecht draw that conclusion after a study of leaf stomatal frequencies in Limburg sediment cores. Fossil stomatal frequency analysis shows strong changes in atmospheric CO2-content in the last eight hundred years. These CO2-changes correspond to 30% of the current human-induced increase. These results show that natural CO2 changes have been large enough to contribute to climate changes over the last thousand years.

This contradicts an assumption of the Inter-Governmental Panel on Climate Change (IPCC). The IPCC assumes that the effects of natural CO2 changes on the climate change in the last thousand years have been negligible. A better understanding of natural CO2 variations leads to a better prediction of the future effects of CO2 increase on the climate.

CO2 is used by plants as building material. Plants adjust the amount of openings on the leaf surface (stomata) to the amount of CO2 in the air. If there is more CO2, fewer plant stomata are needed to guarantee sufficient CO2 absorption. So the number of stomata on fossil leaves can be used to reconstruct the quantity of CO2 in the atmosphere of the past.

The results of this research are published this week in PNAS Early Edition as: Thomas B. van Hoof et al. "A role for atmospheric CO2 in preindustrial climate forcing

Source. (In Dutch. Translation by JR)

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