Climate Central : “April fell first. It lasted through May. Now June will be the third month in a row with average carbon dioxide levels above 400 parts per million.”  

“Atmospheric concentrations of the greenhouse gas, which helps drive global warming, haven’t been this high in somewhere between 800,000 and 15 million years.”  

“It will be the first time in recorded history with this many weeks in a row of such high atmospheric concentrations of CO2.”