Recent global warming and climate change studies frequently assume that the rise in atmospheric CO2 is entirely due to human emissions. In particular, the assumption is based on a figure of CO2 concentration of 280 ppm at the end of the pre-industrial period. However, this assumption reveals itself to be contradicted by an examination of the relevant underlying data. At least, this assumption cannot be fully trusted. This paper points out in plain language the flaws in the fundamentals of the relevant climate change research, using as little technical terminology as possible. Furthermore, some clarification is made in the Appendix, to address typical misunderstandings of the author’s previous paper, that have been seen discussed in the Internet.
