Every year at this time, headlines proclaim that carbon dioxide in the atmosphere has climbed to record high levels. But that really shouldn't be all that surprising, given that CO2 has risen to a new high every single year but one since direct measurements began in 1958.
Now, however, an arguably more meaningful milestone has been passed.
The National Oceanic and Atmospheric Administration reports that in May, the concentration of CO2 in the atmosphere peaked at a level 50 percent higher than the pre-industrial average, before we humans began widespread burning of fossil fuels.
NOAA's measurements of atmospheric carbon dioxide at its Mauna Loa observatory in Hawaii averaged 420.99 parts per million during May. There hasn't been that much CO2 in the atmosphere since an episode in the geologic record known as the Pliocene Climate Optimum — which occurred more than 4 million years ago.
At that time, with comparable ...
