Plants take in CO2, and excrete O2. Animals eat plants, and combine plant matter with O2 – the waste gas of plants. The limit to life on Earth is the efficiency of plants fixing CO2.
So cO2 levels have not changed since the little ice-age. Hard data has been published on this. Even in new scientist – who have been pushing ACC.
Any scientist who does not know these basic facts does not deserve a place teaching at high school. So any scientist who has ever thought Global Warming or Climate Change had merit, should not be working in academia.