Fifty years of carbon dioxide (CO2) measurements in the background atmosphere of SE Australia

P. Fraser, R. Langenfelds, N. Derek, P. Krummel, Z. Loh, CSIRO Oceans and Atmosphere, Aspendale, Victoria

March 2022

In a landmark paper in Nature in 1973¹, CSIRO scientists John Garratt and Graeme Pearman announced the first results of a new CSIRO program to measure atmosphere-ocean carbon dioxide (CO₂) fluxes in the Southern Hemisphere:

‘An atmospheric carbon dioxide monitoring program, based on the collection of discrete air samples from aircraft, was initiated in early 1972 at the CSIRO Division of Atmospheric Physics in Australia’.

Thus began CSIRO’s innovative and globally important greenhouse gas (GHG) research program², measuring (Figure 1) and modelling CO₂ in the mid- to high latitudes of the Southern Hemisphere. The program subsequently expanded to include a range of non-CO₂ GHGs, for example chlorofluorocarbons – CFCs from around 1975.

This CSIRO led work helped support the establishment in 1976 of the iconic Kennaook Cape Grim baseline station⁴, in partnership with the Australian Bureau of Meteorology.

CSIRO’s CO₂ and non-CO₂ GHG data, their interpretation and modelling, have been integral to every international assessment of climate change science and ozone depletion science (of which there have been 6 since 1990 and 12 since 1985, respectively).

The first air samples in this program were collected on Tuesday 21 March 1972 at 4.0 km over the middle of Bass Strait, with a recorded CO₂ concentration of 327 ppm (parts per million molar). 50 years later, the mean baseline CO₂ concentration (413 ppm) recorded at Kennaook / Cape Grim in early 2022 was 413 ppm. That is 26‑27% higher than when the program commenced, and 48% higher than CSIRO’s records of pre-industrial (circa 1750) CO₂ concentrations, based on air extracted from Antarctic ice-cores (typically quoted as 278 ppm).

¹Garratt, J. R. and G. I. Pearman, Large-scale CO₂ fluxes in the Southern Hemisphere troposphere, Nature, 242, 54-56, 1973, doi.org/10.1038/physci242054a0, 26 March 1973.

²Pearman, G. I., J. R. Garratt and P. J. Fraser, CSIRO high-precision measurements of atmospheric CO₂ concentration in Australia. Part 1: Initial motivation, techniques and aircraft sampling, Historical Records of Australian Science, 28 (2) 111 – 125, 2017, doi.10.1071/HR17014.

³Fraser, P. J., G. I. Pearman and N. Derek, CSIRO non-carbon dioxide greenhouse gas research. Part 1: 1975-1990, Historical Records of Australian Science, 29 (1), 1-13, 2018, doi.10.1071/HR17016.

⁴Pearman, G. I., P. J. Fraser and J. R. Garratt, CSIRO high-precision measurements of atmospheric CO₂ concentration in Australia. Part 2: Cape Grim, surface CO₂ measurements and carbon cycle modelling, Historical Records of Australian Science, 28 (2,) 126 – 139, 2017, doi.10.1071/HR17015.