Observed Atmospheric CO2 Hits 400 Parts Per Million

Over at Slashdot:

Over the past month a number of individual observations of CO2 at the Mauna Loa Observatory have exceeded 400 parts per million. The daily average observation has crept above 399 ppm, and as annually the peak is typically in mid-May it seems likely the daily observation will break the 400 ppm milestone within a few days. This measure of potent greenhouse gas in the atmosphere should spark renewed discussion about the use of fossil fuels. For the past few decades the annual peak becomes the annual average two or three years later, and the annual minimum after two or three years more.

One should always worry when something changes dramatically.