There is no such planetary boundary. CO2 ppm concentrations have been higher than 1000 ppm for most of Earth's history. To this day, the vast majority of plant

There is no such planetary boundary. CO2 ppm concentrations have been higher than 1000 ppm for most of Earth's history. To this day, the vast majority of plant species are C3 carbon-fixated plants, which absolutely thrive under CO2 fertilization of between 1000 and 2000 ppm with some plant species benefitting all the way up to 4000 ppm. Source: Effect of CO2 Concentration on Growth of Sugar-beet, Barley, Kale, and Maize https://academic.oup.com/aob/article-abstract/31/4/629/121127 https://academic.oup.com/aob/article-abstract/31/4/629/12112...