Atmospheric carbon dioxide continued its rapid rise in 2019, with the average for May peaking at 414.7 parts per million (ppm) at NOAA’s Mauna Loa Atmospheric Baseline Observatory. The measurement is the highest seasonal peak recorded in 61 years of observations on top of Hawaii’s largest volcano and the seventh consecutive year of steep global increases in concentrations of carbon dioxide (CO2), according to data published today by NOAA and Scripps Institution of Oceanography. The 2019 peak value was 3.5 ppm higher than the 411.2 ppm peak in May 2018 and marks the second-highest annual jump on record. The concentration of CO2 in the atmosphere increases every year, and the rate of increase is accelerating.
— source noaa.gov | Jun 4, 2019
CO2 level was at 415 ppm only in the Pliocene era between 3 and 5 million years ago.