Climate Central: The new year has only just begun, but weve already recorded our first days with average carbon dioxide levels above 400 parts per million, potentially leading to many months in a row above this threshold, experts say. The Scripps Institution of Oceanography records of atmospheric carbon dioxide levels show that Jan. 1 was the first day of the new year above that concentration, followed by Jan. 3 and Jan. 7. Daily averages have continued at this level or higher through Jan. 9, though they could...