Since around 1750, human activities have caused increases in well-mixed greenhouse gas (GHG) in the atmosphere and is still continuing. As per the latest IPCC report, the 2019 annual average of carbon dioxide (CO2) is 410 ppm, that of methane (CH4) is1866 ppb, and that of nitrous oxide (N2O) is 332 ppb. Other GHG concentrations in 2019 were: PFCs (109 ppt CF4 equivalent); SF6 (10 ppt); NF3 (2 ppt); HFCs (237 ppt HFC-134a equivalent); other Montreal Protocol gases (mainly CFCs, HCFCs, 1032 ppt CFC-12 equivalent). ( Source: Sixth Assessment Report (ipcc.ch))