claim: Without human intervention, the concentration of CO2 has climbed as high as 7,000 parts per million ( ppm ) in prior eras, whereas at present the concentration is just over 400 ppm.
evidence: Global annual mean CO 2 concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century to 415 ppm as of May 2019.