The above graph is certainly convincing evidence of a remarkably rapid increase of atmospheric CO2 since 1800. Note how there is a very good match between the most recent ice core data and the actual measurements made at Mount Mauna Loa in Hawaii. Note also that Mauna Loa measurements have been confirmed at other observatories around the world, such as Cape Grim in Tasmania. There can certainly be little doubt about the accuracy of the data after about 1950.
About ten years ago I saw the Law Dome data, now included in the above graph, which all but convinced me that something very serious and unprecedented was happening to CO2 concentrations in the atmosphere so I started looking further afield to find other data and other arguments which would either support or cast doubt on this view.
The data prior to about 1700 looks almost too good to be true because it is so very flat and smooth. Perhaps something else is going on. It has been pointed out (notably by Murray Salby, the guy who was fired by Macquarie University) that, maybe, over time, the CO2 trapped in bubbles in ice cores can diffuse between different layers, so smoothing any ups and down of its variation over time.
Then I found out about stomata at (https://www.geocraft.com/WVFossils/stomata.html).
Stomata are the tiny “mouths” in leaves through which a plant absorbs its “food”, CO2. When concentrations of CO2 are high the plant needs fewer stomata to obtain the required amount of CO2 and when low the opposite is the case. Hence fossil leaves provide an alternative proxy to ice cores for ancient CO2 concentrations. As we can see in the diagram, the two do not match. The stomata densities indicate that CO2 levels were both higher and more variable during the last 1000 years than indicated in the upper diagram. There are two conflicting stories. It’s a “he said, she said” situation.
A further piece of information is the Bomb Test Curve:
There is a mathematical description in TFC, Chapter 13. Suffice to say here that we can conclude that residence time of CO2 in the atmosphere is only 10 years and that less than 20 percent of recent increases in atmospheric CO2 are anthropogenic in origin, the rest comes out of the deep ocean in regions of upwelling. It follows that the ice core graph indicates that either there has been a dramatic recent change in deep ocean circulation or there is something wrong with the ice core proxy CO2 methodology and the stomata data is correct.