Data from the Mauna Loa Observatory in Hawaii showed that carbon dioxide levels surpassed 415 parts per million on Friday, May 10, 2018, a new historic milestone. CO2 levels millions of years ago were higher than 2019 levels, but Earth’s temperatures were also much higher. In the 800,000 years before the Industrial Revolution, CO2 levels didn’t surpass 300 ppm.
By Ryan W. Miller and Doyle Rice. USA TODAY. May 13, 2019.