Over the past 150 million years, carbon dioxide had been drawn down steadily (by plants) from about 3,000 parts per million to about 280 parts per million before the Industrial Revolution. If this trend continued, the carbon dioxide level would have become too low to support life on Earth. Human fossil fuel use and clearing land for crops have boosted carbon dioxide from its lowest level in the history of the Earth back to 400 parts per million today.
At 400 parts per million, all our food crops, forests, and natural ecosystems are still on a starvation diet for carbon dioxide. The optimum level of carbon dioxide for plant growth, given enough water and nutrients, is about 1,500 parts per million, nearly four times higher than today. Greenhouse growers inject carbon-dioxide to increase yields. Farms and forests will produce more if carbon-dioxide keeps rising.
We have no proof increased carbon dioxide is responsible for the earth’s slight warming over the past 300 years. There has been no significant warming for 18 years while we have emitted 25 per cent of all the carbon dioxide ever emitted. Carbon dioxide is vital for life on Earth and plants would like more of it. Which should we emphasize to our children?