The present elevated atmospheric CO2 levels last occurred 3 million years ago.<quoted text>CO2 isn't toxic at atmospheric levels. Quite the opposite, it's necessary for life.
Show why elevated levels are necessary for life. You can't.
But they are behind the present global climate change and first man-made extinction event.
From 1751 to 1995, the cumulative global total CO2 emissions from fossil fuel production were 250x10^^9 tonnes C. Only 25% of this total was emitted by 1950, 50% by 1973, and 75% by 1985.