Atmospheric CO2 measured at Mauna Loa Observatory reached a record high of 417.1 parts per million (ppm) in May 2020 despite COVID-19 restrictions in place. This is the highest monthly reading ever recorded, scientists from NOAA and Scripps Institution of Oceanography said. It is 2.4 ppm higher than the 2019 peak of 414.7 ppm recorded in May 2019.