That constitutes a rise of 1.41ppm since October, which is “normal” in contemporary times. It also means that the yearly average value is going to be very nearly 390ppm for the first time in recorded history. Through November, this year’s average is 389.78ppm. If December 2010’s reading rises over December 2009’s at a rate seen in recent years, the yearly average will fall just short of the 390ppm threshold.
2010 is going to be the last year the yearly average is 390ppm or below for a long time. The average needs to get back below 350ppm and stay there if catastrophic global warming is going to be classified as fiction rather than fact. The last time the yearly average was below 350ppm was back in 1987. That’s 23 years of slowly inexorable rising CO2 concentrations that we need to reverse.
Of course, the only way to reduce the CO2 concentrations in time to prevent large-scale global warming disruptions is to reduce our yearly emissions. As this pdf from NASA researchers shows, emissions (the red line) will have to be greatly reduced in order to bring atmospheric concentrations back down.
If the rate of CO2 concentration increase average over the past 10 years continues, the yearly average will pass 400ppm in 7 years. Countries are talking about reducing their emissions by significant margins by 2020. That has to happen if 400ppm and higher CO2 concentrations are to be avoided.