The following analytical results for major greenhouse and related gases are excerpted from
the WMO WDCGG Data Summary (WMO WDCGG No. 42)
, October 2018.
Carbon Dioxide (CO2)
The level of carbon dioxide (CO2
), which contributes the most to the increase in anthropogenic radiative forcing, has been increasing since the beginning of the industrial era.
The global average mole fraction of CO2
reached a new high of 403.3±0.1 ppm in 2016, which is 145% of the pre-industrial level (in 1750).
The record increase of 3.3 ppm in the annual mean from 2015 to 2016 was greater than the previous record increase from 2012 to 2013 and 50% above the average growth rate over the last decade (about 2.2 ppm/year).
The global growth rate of CO2
shows significant interannual variability driven by natural processes.
Large interannual changes in 1987/1988, 1997/1998, 2002/2003, 2009/2010 and 2015 partly resulted from warmer conditions caused by El Niño-Southern Oscillation (ENSO) events.
The exceptionally low growth rate in 1992, including negative values in northern high latitudes, may have been due to low global temperatures following the eruption of Mount Pinatubo in 1991.
Variations in CO2
mole fraction can be seen on seasonal scales.
The seasonal amplitudes are large in northern high and mid-latitudes.
In the Southern Hemisphere the seasonal cycle is very weak.
) is the second most significant greenhouse gas which is largely influenced by anthropogenic activity and whose level has been increasing since the beginning of the industrial era.
The annual average mole fraction was 1853±2 ppb in 2016, an increase of 9 ppb since 2015.
The mean annual absolute increase during the last 10 years was 6.8 ppb/year.
The mole fraction is now 257% of that in the pre-industrial period.
The latitudinal gradient of CH4
mole fraction is large from the northern mid-latitudes to the tropics, suggesting that the major sources of CH4
are located in the Northern Hemisphere.
growth rates decreased significantly in all latitudinal zones in the 1990s.
However, both hemispheres experienced high growth rates in 1998, caused by the higher than average global mean temperature.
The global growth rates were generally low from 1999 to 2006, except during the El Niño event of 2002/2003, but since 2007 the renewed increase in CH4
mole fractions is observed.
mole fractions vary seasonally, being relatively high in winter and low in summer.
The seasonal amplitudes of CH4
are large, not only in the Northern Hemisphere but also in southern high and mid-latitudes which are associated with methane sinks.
Nitrous Oxide (N2O)
Nitrous oxide (N2
O) is an important greenhouse gas whose level is increasing globally.
O data submitted to the WDCGG show that mole fractions are increasing in both hemispheres.
The global mean mole fraction reached a new high of 328.9±0.1 ppb in 2016, which is 0.8 ppb higher than that in the previous year.
This increase is comparable with the mean annual absolute increase during the last 10 years (0.90 ppb/year).
The 2016 mole fraction corresponds to 122% of that in the pre-industrial period.
The interhemispheric difference in mole fraction is 1.0 ppb (averaged over the years 1980 to 2016), indicating that the majority of N2
O sources are situated in the Northern Hemisphere.
Halocarbons and Other Halogenated Species
Halocarbons, most of which are anthropogenic and generated since the 20th century, are potent greenhouse gases, with some also acting as ozone-depleting compounds.
Levels of some halocarbons (e.g.
CFCs) increased in the 1970s and 1980s, but this increase has almost ceased by now, due to the production and consumption control of halocarbons under the Montreal Protocol on Substances that Deplete the Ozone Layer and its subsequent Adjustments and Amendments.
However, some substances targeted by the Kyoto Protocol but not regulated by the Montreal Protocol, such as HFCs and SF6
, are increasing.
The mole fraction of CFC-11 peaked around 1992 and then started decreasing.
The mole fraction of CFC-12 increased until around 2003 and then started decreasing gradually.
The mole fraction of CFC-113 stopped increasing in the 1990s, followed by a slight decrease over about twenty years.
The mole fractions of HCFCs, which are used mainly as substitutes for CFCs, have increased significantly during the last two decades.
However, the growth of HCFC-141b and HCFC-142b mole fractions has decelerated over the last decade.
The mole fraction of Halon-1211 has decreased since 2005, and the growth of Halon-1301 mole fractions has decelerated over the last several years.
The mole fraction of CCl4
was maximal around 1991 and has since decreased slowly.
The mole fraction of CH3
peaked around 1992 and decreased thereafter.
The mole fractions of HFC-134a, HFC-152a and SF6
are increasing, but the growth of HFC-152a has decelerated over the last decade.
Carbon Monoxide (CO)
Carbon monoxide (CO) is not a greenhouse gas in itself, but is an important part of the global carbon cycle since it influences the mole fractions of greenhouse gases through reactions with hydroxyl radicals (OH).
In 2016, the global mean mole fraction of CO was 90±1 ppb.
The mole fraction is higher in the Northern Hemisphere and lower in the Southern Hemisphere, suggesting substantial anthropogenic emissions in the Northern Hemisphere.
There is a large interannual variability of CO growth rates.
The growth rate increases are mainly attributed to biomass burning emissions during El Niño conditions.
The monthly mean mole fractions show seasonal variations, with large amplitudes in the Northern Hemisphere and small amplitudes in the Southern Hemisphere occurring in opposite phase.