This paper presents new evidence that in the past, rapid increases in atmospheric CO2 concentrations resulted in ocean acidification, which resulted in large numbers of marine species going extinct, which resulted in large numbers of land species going extinct. This shouldn't really come as a surprise to anyone. The only question is at what level of CO2 this happened in the past, and how this compares to the present day. That information, unfortunately, is not in the abstract, and I don't have access to the full article.