3. CO2 Measurements in Atmosphere and Ice Cores


Houghton et al. (1990) claim in their section 1.2.5 three evidences that the contemporary atmospheric CO2 increase is anthropogenic: First, CO2 measurements from ice cores show a 21% rise from 280 to 353 ppmv (parts per million by volume) since pre-industrial times; second, the atmospheric CO2 increase closely parallels (sic!) the accumulated emission trends from fossil fuel combustion and from land use changes, although the annual increase has been smaller each year than the fossil CO2 input [some 50% deviation, e.g. Kerr, 1992]; third, the isotopic trends of 13C and 14C agree qualitatively (sic!) with those expected due to the CO2 emissions from fossil fuels and the biosphere.

Jaworowski et al. (1992 a, 1992 b) reviewed published CO2 measurements from ice cores, and emphasized that the pre-industrial atmospheric CO2 concentration, according to early accurate analyses, was many times larger (measurements up to 2450 ppmv) than the present atmospheric value. They also pointed out that CO2 variations in ice is mainly an artificial effect of a large number of natural physical-chemical processes in ice and the recovered ice cores. These effects dominate over the eventual traces of anthropogenic CO2. Criticism of the methodology has also independently been presented by Heyke (1992 a, 1992 b, 1992 c).

Jaworowski et al. (1992 a) have presented a number of criticisms regarding the methodology of atmospheric CO2 measurements, including spectroscopic instrumental peak overlap errors (from N2O, CH4, and CFCs in the air). They also pointed out that the CO2 measurements at current CO2observatories use a procedure involving a subjective editing (Keeling et al., 1976) of measured data, only representative of a few tens of percent of the total data. There are also fundamental problems connected with the use of stable carbon isotopes (13C/12C) in tree rings for model calculations of earlier atmospheres' CO2 concentration, a method which now seems to have been abandoned (Jaworowski et al., 1992 a).

The third evidence, based on carbon isotopes, will be discussed below in Section 5.

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Last Updated June 20, 1997