I think it would be hard to directly study the ~1/3, ~320-420ppm increase in background CO2 levels over the last ~60 years: https://www.climate.gov/news-feature

I think it would be hard to directly study the ~1/3, ~320-420ppm increase in background CO2 levels over the last ~60 years: https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide https://www.climate.gov/news-features/understanding-climate/... Maybe raising rats in different CO2 levels over several generations. I would be interested in the results of a study like that.