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: Human activities since the beginning of the Industrial Revolution ( around 1750 ) have produced a 45% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 415 ppm in 2019.