Will increased carbon dioxide levels actually benefit planet?
William Happer
Easily spotted by their honeycomb shape, open-cell clouds
are one of the most common cloud formations, found on the
backside of low pressure systems and skirting the edges of
every continent. (Photo/Caption: B. Keim/Wired Science)
Supposed ill effects of more CO2 are from flawed computer models in which water vapour and clouds multiply the modest direct warming by factors of up to 10.
Did the world have just the right concentration of carbon dioxide at the pre-industrial level of 270 parts per million? Reading breathless media reports about CO2 "pollution" and about minimising our "carbon footprints", one might think that the earth cannot have too little CO2. Humans and most other animals would do fine in a world with no atmospheric CO2 - but most plants stop growing if CO2 levels drop much below 150 ppm, so we would starve to death without at least this minimal amount. We are probably better off with our current 390 ppm than with the preindustrial 270 ppm, and we would be better off with still more CO2. For example, there is evidence that California orange groves are about 30 percent more productive today than they were 150 years ago because of the increase of atmospheric CO2.
What atmospheric levels of CO2 would be a direct threat to health? Both the United States Navy and NASA have performed extensive studies of human tolerance to CO2. As a result of these studies, the navy recommends an upper limit of about 8,000 ppm for cruises of 90 days and NASA recommends an upper limit of 5,000 ppm for missions of 1,000 days. We conclude that atmospheric CO2 levels should be above about 150 ppm to avoid harming green plants and below about 5,000 ppm to avoid harming people.