CO2 hits 400 ppm and ...
Atmospheric concentration of carbon dioxide temporarily topped the 400ppm mark for a few hours at the Mauna Loa observatory in Hawaii precipitating a media frenzy. Typical of the hype is this story from the New York Times which begins: “The level of the most important heat-trapping gas in the atmosphere, carbon dioxide, has passed a long-feared milestone, scientists reported Friday, reaching a concentration not seen on the earth for millions of years.” There are two errors of fact in that sentence: 1) water vapor is the most important heat-trapping gas, and 2) CO2 concentrations above 400ppm were reported from the 1820s and from the 1940s.
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Cyanobacteria, around since at least 3.8 billion years ago were growing and emitting oxygen. At some point about 2.5 billion years ago, oxygen in the oceans reached a critical point that caused iron and manganese to precipitate, forming our banded iron formations. Once the iron was used up, the oxygen began to increase in the atmosphere. Eventually, the oxygen destroyed the methane and produced carbon dioxide and water. Since methane is 65 times stronger than carbon dioxide, its destruction lead to the ice age.