Huffington Post: Scientists monitoring global atmospheric carbon dioxide concentrations report that, for the first time in human history, CO2 levels could soon rise above 400 parts per million for a sustained period of time in much of the Northern Hemisphere.
Hourly readings have surpassed 400 ppm in the past week, but daily averages remain just below 400, reported The Guardian. Daily readings are expected to surpass 400 ppm in early May. They will reach their annual peak by mid-month.
The measurements come...