According to the most recent report from the Mauna Loa Observatory, world CO2 concentrations reached a record 396.8 PPM in February.
Considering that we have three more months of seasonally increasing world CO2 values, it is possible that 2013 will see CO2 levels break 400 PPM for the first time in at least 3 million years.
The last time CO2 levels were this high was during the Pliocene epoc. This geological period, occurring about 2.5-5.3 million years ago, exhibited CO2 averages in the range of 365 to 410 ppm.
During the Pliocene, no ice covered Greenland or West Antarctica. Sea levels during the Pliocene were about 75 feet higher than they are today.
For February 2013, world CO2 levels were 3.26 PPM higher than CO2 levels in February of 2012. On average, world CO2 levels are increasing at a rate of 2.2 parts per million each year (but ramping higher). At this rate of increase, it will be less than five years before world CO2 levels exceed that of the Pliocene and begin to enter a range prevalent during the Miocene of around 400-600 ppm CO2.
Early Miocene was a time when no glaciers covered the poles. So pushing world CO2 values out of the range of the Pliocene and into that of the Miocene presents a serious amplification of already challenging climate difficulties.