Evidence of variability of atmospheric CO2 concentration during the 20th century

Presenting person: Ernst-Georg Beck, Gymnasium Merian-Schule in Freising
Th. 2008-07-17 (16:15), H 6

Since the 19th century, use of chemical methods has provided reliable atmospheric CO₂ gas analyses results that have been obtained predominantly from the northern hemisphere. These direct chemical analyses results provide information on past atmospheric CO₂ concentrations in addition to the modern direct atmospheric CO₂ measurements since 1958 and the indirect reconstructions of past atmospheric CO₂ from ice cores. Comprehensive literature indicates that the chemical methods have provided a systematic accuracy within ± 3 Vol% since 1857. Optimization through the 20^th century resulted in numerous sampling round the world on land and sea resulting in systematic sampling and analysis of more than 90,000 CO₂ values near ground, sea surface and up to the stratosphere when around 1960 the modern NDIR spectroscopic method was introduced. Comparison of measurements using old wet chemical and new physical methods in 1958 and 1967 on sea and land reveal a systematic analysis difference of about 10 ppm - new procedures compared to the old. Wet chemical analyses indicate that during the past 2 centuries there were three atmospheric CO₂ maxima in the northern hemisphere. These maxima were as high as about 400 ppm in average over land and sea. The chemical analysis results indicate that atmospheric CO₂ concentration – including its peak around 1942 – has about 80% correlation with the arctic sea surface temperature (SST) during the 20th century. Detailed analysis of CO₂, weather and oceanographic data during the arctic warming since 1918 to 1939 indicate a strong warming of the Northern Arctic Ocean with a subsequent decrease of CO₂ absorption in distinct absorption hotspots (e.g. near Spitsbergen) as a cause of the increased decadal atmospheric CO₂ levels that is not seen in the ice core records.

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