SCC Volume 3.4
Atmospheric CO2 concentrations have been measured since the beginning of the 18th century by chemical analysis with remarkable precision. Since then, methods have changed, and higher precision is achieved.
The first observers discovered daily and yearly variations related to plant growth, distance from sea, elevation, and meteorological conditions. In 1938 an infrared gas analyzer was invented, and the first continuous monitoring physical device, later called NDIR was introduced. With this technique continuous observations were started at Mauna Loa volcanic peak at Hawaii around 1960.
To create a continuous curve which followed the history of anthropogenic emission, the chemical observations were heavily manipulated, and a bandy-stick type curve was created. From ice-core drillings it was believed to be possible to measure the CO2content in bubbles in the ice far back in time. Surprisingly they showed higher level in 1890’ies, than recorded at Mauna Loa in 1960. This led to the idea that the ice bubbles were open for CO2 about 80 years later than the age of the bubble, and the bandy stick curve was restored. A peak of nearly 0.04 % CO2 in about 1940 in the chemical observations was edited away by C. Keeling who started the Mauna Loa observations.
Continue Reading: Challenges in Estimating Atmospheric CO2. By Jan-Erik Solheim