dw - CO2 level rose to values sometimes ​​of the order of 7000, 8000, 9000 ppm, which considerably exceeds the paltry 400 ppm that we have today. Not only did life exist in those far-off times when CO2 was so present in large concentration in the atmosphere, but plants such as ferns commonly attained heights of 25 meters. Reciprocally, far from benefiting the current vegetation, the reduction of the presence of CO2 in the atmosphere would be likely to compromise the health, and even the survival, of numerous plants. To fall below the threshold of 280 or 240 ppm would plainly lead to the extinction of a large variety of our vegetal species. < >