CO2 earth (@@CO2_earth) tweeted Mar 29, 2017: 📈409.47 parts per million (ppm) #CO2 in atmosphere Mar. 28, 2017🎖2nd HIGHEST DAY IN HISTORY🎖#NOAA Mauna Loa data via https://t.co/PTTkLiy4Xs https://t.co/plRXRS6AbI (https://twitter.com/CO2_earth/status/…)