An average of 393.18ppm CO2 concentration was measured at NOAA’s Mauna Loa, Hawai’i’s Observatory during April 2011.
That value is the highest in recorded history. Last year’s 392.49 was the previous highest April value ever recorded. This year’s value is 0.69ppm higher than April 2010. It is 0.76ppm higher than March 2011.
A rough extrapolation of the last few months’ concentrations projects out to 394-395ppm in May, the month during which the yearly maximum concentration is typically recorded.
This will likely be the last year that CO2 concentrations will fall below 390ppm during any calendar month. The aggressive march toward 400ppm continues. Keep in mind that scientists have recommended that 350ppm is the current target for which humanity should aim in order to keep climate extremes from overwhelming our civilization.