RECONSTRUCTION OF THE PAST ATMOSPHERIC
CARBON DIOXIDE CONCENTRATION

Reconstruction of the atmospheric CO2 concentration over the past 62000 years
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Download postscript file with reversed time axis.

The concentration of atmospheric CO2 (the most important greenhouse gas after water vapour) is increasing since the beginning of industrialisation from its pre-industrial value of about 280 ppmv (parts per million by volume) to its present value of 365 ppmv . In order to understand the impact of this strong perturbation on the carbon cycle and on climate it is important to investigate the global carbon cycle on all time scales. Direct measurements of atmospheric CO2 exist since 1958. A reliable reconstruction of the concentration of atmospheric CO2 in the past, a prerequisite for the understanding of the long term variations, is only possible by measurements on air which is enclosed in bubbles of polar ice. Such measurements have been done since 20 years in different laboratories with different methods. In all laboratories a sample of ice (mainly from Antarctic drill sites) of 6 to 1500 g is crushed or ground under vacuum without melting. The extracted air is then measured by infrared laser absorption spectroscopy, gas chromatography or volumetry. The analytical uncertainty is 1.2 to 5 ppmv, depending on sample size, extraction method and analytical procedure.

The measuring procedure in Bern is the following: From each depth interval up to six samples of 2.5·2.5·1.5 cm3 volume (resulting in a depth resolution of 2.5 cm) are cracked in an evacuated and cooled needle cracker. To measure the CO2 concentration of the extracted gas, an infrared laser is tuned several times over the absorption line of a vibration-rotation transition of the CO2 molecule. Calibration is routinely done using reference gases from the Scripps Institution of Oceanography. Measurements on bubble-free single crystal ice samples, to which reference gas is added, yield an estimate of ± 1.5 ppmv for the analytical uncertainty of the device.

Recent Publications

• Stauffer, B., T. Blunier, A. Dällenbach, A. Indermühle, J. Schwander, T. Stocker, J. Tschumi, J. Chappellaz, D. Raynaud, C.U. Hammer, H.B. Clausen, 1998, Atmospheric CO₂ concentration and millennial-scale climate change during the last glacial period. Nature 392, 59-62 (Abstract)

• Marchal, O., T.F. Stocker, F. Joos, A. Indermühle, T. Blunier, J. Tschumi, 1999, Modelling the concentration of atmospheric CO₂ during the Younger Dryas climate event. Climate Dynamics, 15, 341-354 (Abstract) (Download pdf-file)

• Indermühle, A., T.F. Stocker, F. Joos, H. Fischer, H.J. Smith, M. Wahlen, B. Deck, D. Mastroianni, J. Tschumi, T. Blunier, R. Meyer, B. Stauffer, 1999, Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica. Nature 398, 121-126 (Abstract)

• Indermühle, A., E. Monnin, B. Stauffer, T.F. Stocker, M. Wahlen, 1999, Atmospheric CO2 concentration from 60 to 20 kyr BP from the Taylor Dome ice core, Antarctica. Geophysical Research Letters, 27, 735-738. (Download pdf-file)

Data Links

• Carbon Dioxide Information Analysis Center (CDIAC) : TRENDS Home, Mauna Loa and other data
• NOAA Climate Monitoring & Diagnostics Laboratory (CMDL): Data
• NOAA Paleoclimatology Program: Holocene and glacial data from the Taylor Dome ice core.
• Glacial and transition data from Byrd Station

The most wanted CO₂ figures

For more information and data request please send an email to monnin@climate.unibe.ch