Craig Idso, founder and CEO of the Center for the Study of Carbon Dioxide and Global Change, has debunked climate alarmists' claims that high levels of atmospheric carbon dioxide (CO2) cause a direct threat to health and make plants thicken their leaves and less efficient in sequestering carbon, causing a rise in temperatures and the occasional heatwaves.

According to Idso, CO2 levels would have to surge 36 times above the present concentration before they would even begin to pose a mild health concern. "That value (i.e., 15,000 ppm) will never occur, given it is a factor of ten above the approximate 1,500 ppm atmospheric CO2 limit that scientists think is possible if society utilized all of the currently-known fossil fuel reserves on the planet," he explained.

Subsequently, if CO2 is low in the atmosphere, it poses a threat to humanity.

"The more CO2 the better, in other words," he pointed out in a blog post on Watts Up With That. "CO2 literally is the 'food' that sustains essentially all plants (and animals that consume plants, including humans) on the face of the Earth. And when that food supply is diminished, nature begins to diminish."

He cited a 2020 study that examined the impact of low levels of CO2 on African wood-sorrel (Oxalis pes-caprae). This plant species was a key carbohydrate source for humans during the Middle Pleistocene as they are harvested for their edible underground storage organs (USOs).