Plant photosynthesis has its upper limits. So, self modulating to an extent. I think the article is more insightful around I indoor air quality rather than out

Plant photosynthesis has its upper limits. So, self modulating to an extent. I think the article is more insightful around I indoor air quality rather than outdoor. With respect to outdoor, if CO2 were fully self modulating, isn't the fact it has been consistently raising a counter point to that idea? How does self modulation explain the data showing increases?