Handy Guide to CO2

Luboš Motl has a post on his blog The Reference Frame where he notes the range of interesting CO2 concentrations:

It may be useful to summarize some important values of the CO2 concentration:

• 150 ppm - the minimum concentration below which many plants may face problems to run photosynthesis and stop growing


• 180 ppm - the concentration during ice ages


• 280 ppm - the concentration during interglacials, i.e. also the pre-industrial concentration around 1750


• 391 ppm - the concentration today


• 500 ppm - the concentration around 2060-2070 (unlikely that before 2050 as they claim)


• 560 ppm - the concentration around 2080-2110 (the "doubled CO2" relatively to the pre-industrial values) relevant for the calculations of climate sensitivity)


• 700 ppm - the concentration in an average living room


• 900 ppm - concentration in an average kitchen


• 1,270 ppm - the concentration used to double the growth of Cowpea in a famous video


• 4,500 ppm - the concentration 400 million years ago; see other values in geological epochs


• 10,000 ppm - sensitive people start to feel weaker


• 40,000 ppm - the concentration of CO2 in the air we breath out


• 50,000 ppm - toxic levels at which the animals like us get weaker in hours; the value is 5 percent of the volume

The warming induced by the increase from 391 ppm to 500 ppm is smaller (by about 20%) - because of the logarithmic law - than the warming by the same 109 ppm between 282 ppm and 391 ppm which was about 0.7 °C and pretty much unnoticeable without accurate gadgets and contrived statistical methods.