thumb|left|upright=0.7|The Keeling Curve of atmospheric CO2 abundance. is produced by fossil fuel burning and other activities such as cement production and tropical deforestation.IPCC Fourth Assessment Report, Working Group I Report "The Physical Science Basis" Chapter 7 Measurements of from the Mauna Loa Observatory show that concentrations have increased from about 313 parts per million (ppm) in 1960, passing the 400 ppm milestone in 2013. The current observed amount of exceeds the geological record maxima (≈300 ppm) from ice core data.
thumb|left|upright=07|The Keeling Curve of atmospheric CO2 abundance is produced by fossil fuel burning and other activities such as cement production and tropical deforestationIPCC Fourth Assessment Report Working Group I Report "The Physical Science Basis" Chapter 7 Measurements of from the Mauna Loa Observatory show that concentrations have increased from about 313 parts per million (ppm) in 1960 passing the 400 ppm milestone in 2013 The current observed amount of exceeds the geological record maxima (≈300 ppm) from ice core data