Going up, dangerously higher...According to measurements from the Mauna Loa Observatory in Hawaii, a very remote atmospheric research facility in the middle of the Pacific that has been monitoring atmospheric change since the 1950s, the Earth's atmosphere is right about to reach 400 parts-per-million (ppm) of CO2, a level that was last seen 3 million years ago. The first measurements at the observatory in 1958 had CO2 levels at 317ppm.
The last time CO2 reached the symbolic milestone of 400 parts per million in the atmosphere - in the Pliocene era - temperatures rose by between 3 and 4 degrees and sea levels were between five and 40 metres higher than today. (source)
No need to say that this isn't good news...
As a reminder, 2012 was the hottest year on record in the U.S..