The two squares represent relative levels of nitrogen and oxygen as white (nearly 80%); average water vapour as darker blue (2%); peak water vapour as pale blue (another 2%); and CO2 levels as black (pre-industrial levels about 300 ppm; current levels about 400 ppm; or 0.03% and 0.04%).
The upper square shows represents pre-industrial levels (three blocks) and the lower square represents current levels (four blocks).
Scary stuff, huh?
Debate Magazine
