“CO2 is not a bad gas,” says Valentina Zharkova, a Professor at the Northumbria University in Newcastle, U.K. On the contrary, she points out, every garden centre uses it in its greenhouses to make plants lush and green. “We actually have a CO2 deficit in the world, and it’s three to four times less than the plants would like,” she notes, adding that the proportion of CO2 in the atmosphere has been at much higher levels throughout our planet’s history than it is now.

In fact, over the last 140 million years, the amount of CO2 in the atmosphere has been steadily decreasing and only now slightly starting to rise. It is currently around 420 parts per million (ppm), or 0.042%. 140 million years ago, it was estimated at 2,500 ppm (0.25%), or about six times higher. And it also meant a greener and more biodiverse world. If CO2 were to fall below 150 ppm (0.015%), it would already mean the extinction of vegetation and all other life. We came close to that during the last glacial maximum when it was at 182 ppm (0.018%).