What’s interesting about this article is that it is an excellent example of one piece of the scientific method in action. From the introduction,
“Measurements of carbon dioxide … have been made at Mauna Loa … since 1958 by Scripps … One objective … has been to document global-scale secular CO2 trends. A duplicate, but quasi-independent, program has been underway since June 1974.”
Already the Scripps Institution of Oceanography had been measuring the CO2 concentrations on Mauna Loa since 1958 and had seen an increase of 1.14 ppm (parts per million) per year. As is par for the course, scientists don't rely on one measurement of an important quantity, they seek "reproducible results." In this case, a different method was used by NOAA's Geophysical Monitoring for Climatic Change (GMCC) program to measure the same CO2 concentration. Their result is shown here:
There is obviously an annual variation, but superposed on that is a "secular" increase, that is, one that is monotonic. It keeps on increasing. Even though it is only two years, this secular increase agrees with the earlier result.
What did the earlier result look like? This:
Again, there's a secular increase superposed on an annual variation. Peterson et al. have this to say about the earlier data:
"... the year-to-year increases were quite variable, from less than 0.5 to more than 2.0 ppm. At this time, the GMCC and Scripps records cannot be absolutely compared because of calibration problems..."So, while the two methods were in general agreement, it was difficult to compare two measurements using completely different methods. In any case, more measurements were made, and an absolute comparison was achieved, at least to a level that was consistent with the uncertainties in the original observations.
The scientific method in action!
