CSIRO High-precision Measurement of Atmospheric CO2 Concentration in Australia. Part 1: Initial Motivation, Techniques and Aircraft Sampling

The potential for carbon dioxide (CO2) in the atmosphere to influence global surface temperatures was first recognized in the mid-nineteenth century. Even so, high-precision measurements of atmospheric CO2 concentration were not commenced until the International Geophysical Year (1957–8), following concerns of the climatic impact of increased use of fossil fuels and the concomitant release of CO2 into the atmosphere. In Australia, an early (1960s–70s) interest in the high-precision measurement of CO2 concentration was stimulated by a study of the photosynthesis and respiration of awheat crop. This study conducted in north-easternVictoria during 19717–2 led two young CSIRO scientists, J. R. Garratt and G. I. Pearman, encouraged by their Chief, C. H. B. Priestley, to extend micro-environment CO2 studies to larger-scale measurements of CO2 concentration in the background atmosphere. The significant extension of the observation programme required refined measurement techniques to improve both the precision and absolute comparability with observations made by laboratories overseas. Joined in 1974 by P. J. Fraser, they identified the impact of pressure broadening on calibration techniques used in the non-dispersive infrared absorption method of CO2 concentration measurement. This, in turn, led to improved inter-comparability of CO2 concentration data collected around the globe. Acomprehensive aircraft-based air sampling programmewas established in the early 1970s, leading to increased understanding of the time and space variability of CO2 concentration throughout the depth of the troposphere and lower stratosphere in the mid-latitudes of the Southern Hemisphere. In turn this led to: (i) the establishment of a permanent ground-based observatory at Cape Grim, north-western Tasmania; (ii) the development of carbon cycle models; and (iii) measurements of 12CO2, 13CO2 and 14CO2 relative abundances in current and past atmospheres, the last from air samples trapped in ice cores (described in Part 2, the companion paper). The accumulated data from these studies, together with those collected by international colleagues, form the basis of our understanding of the changes of CO2 concentration over thousands of years. In addition, the data have contributed to our understanding of the mechanisms of past and present biogeochemical cycling of CO2 that provides the predictive basis for future changes in CO2 concentration.