Well, folks, we "got there:" The first weekly average CO2 concentration over 420 ppm at Mauna Loa.

[NNadir]

2. Increased/reduced growth of plants in elevated CO2 situations is a mixed bag.

Some plants do better, others do worse.

One species that is known to do better with elevated CO2 is Toxicodendron radicans. It is discussed in this paper, to which, regrettably I do not have full access, but which states the outcome clearly enough in the Abstract: Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron radicans) (Ziska, L., Sicher, R., George, K., & Mohan, J. (2007). Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron radicans). Weed Science, 55(4), 288-292. doi:10.1614/WS-06-190)

I am aware, vaguely, of articles about other plants, including crop plants, where carbon dioxide level increases have had a baleful effect on growth, and of course, changes in rainfall clearly are a real risk to flora in general.