Ernst-Georg Beck was a honest hard working Scientist. He died of cancer in 2010 but his excellent web site, which has many articles and references, is kept up by his daughter.
Please visit it http://www.biomind.de/realCO2/realCO2-1.htm
Around 1940-1942 several scientists measured CO2 in the atmosphere at levels close to the present in 2011. This can be seen in the graph on the home page of Beck’s web site. One of the Scientists was W Kreutz who made continuous measurements of CO2 three times a day plus other weather related parameters (temperature, radiation, rainfall humidity, wind direction and speed etc) for one and half years 1939-1941. During this period he also made more frequent measurements over shorter periods such as eight days. It is a pity that so-called climate scientists have not made such thorough ( and accurate) measurements of all parameters which are an input (eg radiation) or a result ( eg temperature, humidity, CO2 etc) of weather changes. Kreutz was a chemist who was interested in conditions affecting plant growth. His measurements were published in a Botany Journal and have been overlooked in Climate research until brought to attention of the world by E-G Beck. Beck has scanned the individual pages of the article and that can be downloaded from his web site.
Below is a partial translation of the article by a Dutchman Andre Bijkerk. I can not remember how it came into my file but I hope he does not mind me posting it here.