https://www.dailykos.com/stories/2018/5/4/1762050/-The-last-time-atmospheric-carbon-dioxide-was-this-high-humans-didn-t-exist
"The average concentration of carbon dioxide in the atmosphere was 410.31 parts per million (ppm) for the month of April, according to the Keeling Curve measurement series made at the Mauna Loa Observatory in Hawaii. This marks the first time in the history of the Mauna Loa record that a monthly average has exceeded 410 parts per million. This also represents a 30-percent increase in carbon dioxide concentration in the global atmosphere since the Keeling Curve began in 1958. In March, Scripps Institution of Oceanography at the University of California San Diego observed the 60th anniversary of the data series, the first measurements of which were 315 ppm. The headline comes from Eric Holthaus, who puts it in context: The last time atmospheric carbon dioxide levels were this high, millions of years ago, the planet was very different. For one, humans didn’t exist."
