WMO Greenhouse Gas Bulletin - No.12: The State of Greenhouse Gases in the Atmosphere Based on Global Observations through 2015

The report shows that globally averaged surface mole fractions(3) calculated from this in situ network for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) reached new highs in 2015, with CO2 at 400.0±0.1 ppm, CH4 at 1845±2 ppb(4) and N2O at 328.0±0.1 ppb. These values constitute, respectively, 144%, 256% and 121% of pre-industrial (before 1750) levels. It is predicted that 2016 will be the first year in which CO2 at the Mauna Loa Observatory remains above 400 ppm all year, and hence for many generations [4]. The increase of CO2 from 2014 to 2015 was larger than that observed from 2013 to 2014 and that averaged over the past 10 years. The El Niño event in 2015 contributed to the increased growth rate through complex two-way interactions between climate change and the carbon cycle. The increase of CH4 from 2014 to 2015 was larger than that observed from 2013 to 2014 and that averaged over the last decade. The increase of N2O from 2014 to 2015 was similar to that observed from 2013 to 2014 and greater than the average growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index [8, 9] shows that from 1990 to 2015 radiative forcing by long-lived greenhouse gases (LLGHGs) increased by 37%, with CO2 accounting for about 80% of this increase.