evidence: The concentration of a greenhouse gas is typically measured in parts per million (ppm) or parts per billion (ppb) by volume. A CO2 concentration of 420 ppm means that 420 out of every million air molecules is a CO2 molecule. The first 30 ppm increase in CO2 concentrations took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014.[8][44][45] Similarly, the average annual increase in the 1960s was only 37% of what it was in 2000 through 2007.[46] [...] The major anthropogenic (human origin) sources of greenhouse gases are carbon dioxide (CO2), nitrous oxide (N 2O), methane and three groups of fluorinated gases (sulfur hexafluoride (SF 6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs, sulphur hexafluoride (SF6), and nitrogen trifluoride (NF3)).[89] Though the greenhouse effect is heavily driven by water vapor,[90] human emissions of water vapor are not a significant contributor to warming.