You may remember when the Mauna Loa readings topped 400 ppm of Co2 about 1 year ago.
Now it has stayed above for a full month.

http://www.huffingtonpost.com/2014/04/22/carbon-dioxide-climate-change_n_5187844.html

As of April 20, the level of carbon dioxide in the atmosphere was 401.17 ppm. That figure is based on readings from the Mauna Loa Observatory in Hawaii. The scientists who monitor atmospheric carbon dioxide levels expect that levels will stay above 400 ppm until late June or July.

Tans said that the level of CO2 in the atmosphere is now increasing at a rate that is at least 100 times faster than it has been at any time since record-keeping began. At some point next year or the year after, based on current rates, carbon dioxide levels will rise above 400 ppm and will not be likely to fall below that mark again.

The amount of carbon dioxide that gets naturally absorbed from the atmosphere varies according to the time of year, said Tans. During late spring and early summer in the northern hemisphere, trees and plants take in more carbon dioxide from the atmosphere. But as emissions generated by human activities rise, those cycles can no longer offset them. "We are basically overwhelming natural uptake processes," said Tans.