[palmer]

We just got through the lowest CO2 in the earth's history. Key plant species were struggling and the C4 plants like the ancestor of corn evolved to more efficientiy gather CO2. When a well-watered corn field is growing in full sun the CO2 can drop back to 250 ppm or even 200 from a predawn level of about 500.

We need CO2. At this point we need all we can get. Thanks to technological progress, at some point fairly soon there will be cheap or free energy without CO2, and overage can also be corrected at that point

[zeestephen]

Re: We just got through the lowest CO2 in the earth’s history.

Yes.

About 20,000 years ago, which was also the coldest period during the last glacial, the level of CO2 went to 180 parts per million.

Most botanists agree that 150 parts per million is the point where a massive die off photosynthetic plants will begin.

And when edible plants and grains start dying, a massive die off of human beings is not far behind.

Curiously, after reaching maximum low temperature, the Earth warmed for 800 years BEFORE the level of CO2 began to rise from 180 ppm.