WMO GHG Update: Atmospheric CO2 Up 147% Over Pre-Industrial; CH4 Up 259%, N2O Up 123%
The latest analysis of observations from the WMO GAW Programme shows that globally averaged surface mole fractions(1) calculated from this in-situ network for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) reached new highs in 2018, with CO2 at 407.8±0.1 ppm(2), CH4 at 1869±2 ppb(3) and N2O at 331.1±0.1 ppb. These values represent, respectively, 147%, 259% and 123% of pre-industrial (before 1750) levels. The increase in CO2 from 2017 to 2018 was very close to that observed from 2016 to 2017, and practically equal to the average yearly increase over the last decade. For CH4, the increase from 2017 to 2018 was higher than both that observed from 2016 to 2017 and the average over the last decade. For N2O, the increase from 2017 to 2018 was also higher than that observed from 2016 to 2017 and the average growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index (AGGI) [9] shows that from 1990 to 2018 radiative forcing by long-lived greenhouse gases (LLGHGs) increased by 43%, with CO2 accounting for about 80% of this increase.
Overview of the GAW in-situ network observations for 2018This fifteenth WMO Greenhouse Gas Bulletin reports atmospheric abundances and rates of change of the most important LLGHGs – CO2, CH4 and nitrous oxide N2O – and provides a summary of the contributions of other gases. These three, together with CFC-12 and CFC-11, account for approximately 96%(4) [9] of radiative forcing due to LLGHGs (Figure 1).
The GAW Programme (http://www.wmo.int/gaw) coordinates systematic observations and analyses of greenhouse gases (GHGs) and other trace species. Sites where greenhouse gases have been measured in the last decade are shown in Figure 2. Measurement data are reported by participating countries, and are archived and distributed by the World Data Centre for Greenhouse Gases (WDCGG) at the Japan Meteorological Agency.
The results reported here by WDCGG for the global average and growth rate are slightly different from those reported by NOAA for the same years [10], due to differences in the stations used, in the averaging procedure and a slightly different time period for which the numbers are representative. The World Data Centre for Greenhouse Gases follows the procedure described in detail in the GAW Report No. 184 [11].
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