Carbon dioxide atmospheric concentrations

From Glossary of Meteorology

carbon dioxide atmospheric concentrations

The amount of carbon dioxide in the atmosphere, most commonly expressed as a mixing ratio by volume, usually in units of parts per million by volume (ppmv).

The 2016 global annual mean marine surface concentration of 403 ppmv is more than 40% greater than the preindustrial (i.e., eighteenth century) value of 280 ppmv and 12% above the 1995 value of 360 ppmv.
CO2 trend‎

Fig. 1. The graph shows recent monthly mean carbon dioxide measured at Mauna Loa Observatory, Hawaii. The last four complete years of the Mauna Loa CO2 record plus the current year are shown. Data are reported as a dry air mole fraction defined as the number of molecules of carbon dioxide divided by the number of all molecules in air, including CO2 itself, after water vapor has been removed. The mole fraction is expressed as parts per million (ppm). Example: 0.000400 is expressed as 400 ppm. In the above figure, the dashed red line (diamond symbols) represents the monthly mean values, centered on the middle of each month. The black line (square symbols) represents the same, after correction for the average seasonal cycle. The latter is determined as a moving average of seven adjacent seasonal cycles centered on the month to be corrected, except for the first and last 3.5 yr of the record, where the seasonal cycle has been averaged over the first and last 7 yr, respectively. The last year of data is still preliminary, pending recalibrations of reference gasses and other quality control checks. The Mauna Loa data are being obtained at an altitude of 3400 m in the northern subtropics and may not be the same as the globally averaged CO2 concentration at the surface. (Graph from Ed Dlugokencky and Pieter Tans.) [Editor’s note: this graph is a snapshot in time; the most current data can be found by looking at]

Term edited 26 June 2017.