Hi Jay,
Jay Angler wrote:...if the goldenrod was grown in dirt with fertilizer, it might well show some of the changes for reasons other than the presence of higher levels of CO2.
There were two separate trials conducted (link to study at bottom)
1) Comparing present-day goldenrod to historic goldenrod (which does not directly address your above concern)
2) Conducting an isolated trial where the goldenrod was grown in polytunnels where atmospheric CO2 was the only variable (which does directly address your concern)
The report explains that the confidence in their conclusions from both tests is high: "...the current data do indicate a clear and unequivocal link, both historically and experimentally, between rising [atmospheric carbon dioxide] and a qualitative decline in pollen protein".
Jay Angler wrote:Who was that guy anyway?
He is a professional science communicator. He has a degree in physics engineering and a PhD in science education research.
Finally, I do also dislike how quickly he dismisses (in the video) the idea that soil health does not contribute. However I am comfortable believing the results of the study.
The study -
http://rspb.royalsocietypublishing.org/content/283/1828/20160414