I post on a lot of research and when I do I try to ascertain that where ever it comes from is trustworthy. Some stuff that debunks the hysteria is of questionable quality. This study looks solid to me and is published in a relatively new journal that seems like it is trying to be careful about what gets published there. And the nice thing is that stuff in this journal is open access–free. If you are interested in climate, worth watching this journal.
The article was focused on the frequent assumption that CO2 concentration pre-industrial was 280 parts per million. If you trust CO2 measurement, that concentration has increased rapidly. Not clear that this matters as I am not bought into CO2 levels being the primary factor in climate, in fact I am pretty sure it isn’t. But the hysterics use this level and create their fantasy models. The authors show that this number is likely inaccurate. They go through a number of reasons and inconsistencies. It seems sensible to me, I am not sure how much of a difference there would be in the historical numbers. The recent numbers are likely highly accurate. (SCE Article)
As I said above, the bigger questions in my mind are the extent to which the increase is human driven–I will assume most of it is–and really, is CO2 the control knob? It likely is a factor but given the complexity of feedbacks, and given other climate inputs changing during the same time, I don’t think it is the “control knob” and I suspect other factors, like solar input and clouds are more important. But issues about levels and trends in CO2 are important to address as well.
The Healthy Skeptic is a website about the health care system, and is written by Kevin Roche, who has many years of experience working in the health industry. Mr. Roche is available to assist health care companies through consulting arrangements through Roche Consulting, LLC and may be reached at 
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One of the major problems in the paleo research arena is reliance on low or moderate resolution proxies for temperature and in this case CO2 levels. From these low resolution proxies and sparse proxies in the SH, climate scientists somehow use statistics that result in estimated global temps with very narrow error ranges with high confidence levels. For example for each year between 1900 through 1930, climate scientists have estimated the earths global temp with a margin of error of 0.2c (0.36f).
This paper linked by K roche shows climate scientists have done the same with the estimated CO2 levels