We actually do not know how much carbon dioxide was in Earth’s atmosphere prior to the 1930s. Devices to reliably measure carbon dioxide in the air went through painstaking, slow, bumpy development. Instruments did not really come into their own until around 1930. Because we don’t know the carbon dioxide content of the atmosphere, climate change proponents depend upon unreliable “proxies.” They substitute gas pockets retrieved from ice core samples from deep within ancient glaciers. They hope this will tell us Earth’s ancient atmosphere and the concentration of CO2 in the air. Speculation that air pockets remain exactly the same...