400-ppm milestone has been reached
For the first time monthly mean levels of carbon dioxide above 400 parts per million have been recorded over the entire Arctic and parts of Japan. Globally, it will take another few years before the symbolic level is passed. For 2012 it is estimated that the global average level will be approximately 393 ppm.
Any increase in carbon dioxide in the atmosphere is serious, but the passing of the 400-ppm level is mainly of symbolic significance.
“In fact, we don’t know what a safe level of CO2 would be,” says Pieter Tans of the US National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colorado to New Scientist.
Source: New Scientist, 7 June 2012