We do not know how much carbon dioxide was in Earth's atmosphere prior to the 1930s. Devices to measure carbon dioxide went through a difficult, slow, irregular development. Reliable devices to measure carbon dioxide were available around 1930. "The measurement of carbon dioxide (CO2) was first developed in the early 1900s; however, it was complex and of limited clinical use. " See: Thomas Nowicki; Shawn London, "Carbon Dioxide Detector," National Center for Biotechnology Information. The technology was slowly developed and produced a useable machine only around the year 1930. Guy Stewart Callendar -- who dreamed up the global warming scare...