Atmospheric carbon dioxide levels as indicated by the stable isotope record in wood

Abstract

THE concentration of CO₂ in the atmosphere has increased from about 290 parts per million (p.p.m.) by volume in 1900 (ref. 1) to 323 p.p.m. in 1972 (ref. 2) and this increase is generally held to be due chiefly to combustion of fossil fuels. Indeed by 1970 this artificial mechanism had introduced to the atmosphere an amount of CO₂ equivalent to 22% of the natural or pre-industrial atmospheric inventory³. About half of the added CO₂ seems to have been transferred to the other major reservoirs of the dynamic carbon cycle, the oceans and biosphere. Before examining the threat to global climate and marine life⁴, future CO₂ levels from this source must be predicted. Before such extrapolations can be confidently applied, however, we must fully understand the past response of the atmosphere to fossil CO₂ emission. Since direct measurements of atmospheric CO₂ are either not available or considered unreliable indirect methods of assessing the CO₂ buildup must be invoked. Here a novel and potentially valuable approach is presented.