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The State of Greenhouse Gases in the Atmosphere Using Global Observations through 2016

On-line version of the WMO Greenhouse Gas Bulletin N.13

Executive summary

The latest analysis of observations from the WMO GAW Programme shows that globally averaged surface mole fractions calculated from this in situ network for CO2, methane (CH4) and nitrous oxide (N2O) reached new highs in 2016, with CO2 at 403.3 ± 0.1 ppm, CH4 at 1853 ± 2 ppb and N2O at 328.9 ± 0.1 ppb. These values constitute, respectively, 145%, 257% and 122% of pre-industrial
(before 1750) levels. The record increase of 3.3 ppm in CO2 from 2015 to 2016 was larger than the previous record increase, observed from 2012 to 2013, and the average growth rate over the last decade. The El Niño event in 2015/2016 contributed to the increased growth rate through complex two-way interactions between climate change and the carbon cycle. The increase of CH4 from 2015 to 2016 was slightly smaller than that observed from 2014 to 2015, but larger than the average over the last decade. The increase of N2O from 2015 to 2016 was also slightly smaller than that observed from 2014 to 2015 and the average growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2016, radiative forcing by long-lived greenhouse gases (LLGHGs) increased by 40%, with CO2 accounting for about 80% of this increase.


This thirteenth WMO/GAW annual GHG bulletin reports atmospheric abundances and rates of change of the most-important LLGHGs – CO2, CH4 and N2O – and provides a summary of the contributions of the other greenhouse gases. These three LLGHGs, together with CFC-12 and CFC-11, account for approximately 96% of radiative forcing due to LLGHGs (Figure 1).


Figure 1. Atmospheric radiative forcing, relative to 1750, of LLGHGs and the 2016 update of the NOAA AGGI.

contributions to total radiative forcing

Figure 1 (additional). Changing contribution (in %) of key greenhouse gases in the total radiative forcing of all LLGHG.

The WMO GAW Programme ( coordinates systematic observations and analysis of GHGs and other trace species in the atmosphere. Sites where GHGs have been measured in the last decade are shown in Figure 2. Measurement data are reported by participating countries and archived and distributed by the World Data Centre for Greenhouse Gases (WDCGG) at the Japan Meteorological Agency.

The results reported here by WMO WDCGG for the global average and growth rate are slightly different from the results reported by NOAA for the same years, due to differences in the stations used, differences in the averaging procedure and a slightly different time period for which the numbers are representative. WMO WDCGG follows the procedure described in GAW Report No. 184.

The three GHGs shown in Table 1 are closely linked to anthropogenic activities and interact strongly with the biosphere and the oceans. Predicting the evolution of the atmospheric content of GHGs requires quantitative understanding of their many sources, sinks and chemical transformations in the atmosphere. Observations from the GAW Programme provide invaluable constraints on the budgets of these and other LLGHGs, and are used to assist the improvement of emission inventories and evaluate satellite retrievals of LLGHG column averages. The Integrated Global Greenhouse Gas Information System, promoted by WMO, provides further insights into the sources of GHGs on national and subnational levels.

The NOAA AGGI in 2016 was 1.40, representing a 40% increase in total radiative forcing by all LLGHGs since 1990 and a 2.5% increase from 2015 to 2016 (Figure 1). The total radiative forcing by all LLGHGs in 2016 corresponds to a CO2-equivalent mole fraction of 489 ppm.

Number of stations used for the calculation of the global averages.

CO2 123
CH4 125
N2O 33
CFC11 23
CFC12 24
CFC113 20
CCl4 21
CH3CCl3 24
HCFC141b 10
HCFC142b 14
HCFC22 14
HFC134a 10
HFC152a 9
SF6 24


map of the stations

     Figure 2. The GAW global network for carbon dioxide in the last   decade. The network for methane is similar.


Table 1 provides globally averaged atmospheric abundances of the three major LLGHGs in 2016 and changes in their abundances since 2015 and 1750. Data from mobile stations (blue triangles and orange diamonds in Figure 2), with the exception of NOAA sampling in the eastern Pacific, are not used for this global analysis.


Table 1. . Global annual surface mean abundances (2016) and trends of key GHGs from the WMO/GAW global GHG observational network. Units are dry-air mole fractions, and uncertainties are 68% confidence limits; the averaging method is described in GAW Report No. 184.





Global abundance in 2016

403.3 ± 0.1

1 853 ± 2

328.9 ± 0.1

2016 abundance relative to year 1750*




2015–2016 absolute increase

3.3 ppm

9 ppb

0.8 ppb

2015–2016 relative increase




Mean annual absolute increase during last 10 years

2.21 ppm per year

6.8 ppb per year

0.90 ppb per year

* Assuming a pre-industrial mole fraction of 278 ppm for CO2, 722 ppb for CH4 and 270 ppb for N2O.


Atmospheric CO2 Concentrations Though Time

Discovery of ancient atmospheres in Antarctic ice

By Nancy Bertler (GNS Science and Victoria University of Wellington), Richard Levy (GNS Science) and Jocelyn Turnbull (GNS Science, New Zealand)

paleo co2 data

Reconstructions of atmospheric CO2 over the past 55 million years are generated from proxy data that include boron isotopes (blue circles), alkenones (black triangles) and leaf stomata (green diamonds). Direct measurements from the past 800 000 years are acquired from Antarctic ice cores and modern instruments (pink). Future estimates include representative concentration pathways (RCPs) 8.5 (red), 6 (orange), 4.5 (light blue), and 2.6 (blue).


Over the past 30 years, techniques have been developed to coax tiny air bubbles in Antarctic ice cores to reveal an intricate record of atmospheric GHG concentrations, in particular CO2, CH4 and N2O. Unlike most paleoclimate reconstructions, the GHG record is not a proxy but rather a measurement of past atmospheres obtained from minute parcels of ancient air captured in the ice as new snow accumulating at the top solidifies into ice. The first record was developed by the French scientist Claude Lorius at Dome C and Vostok Station in the 1970s during the height of the cold war, in collaboration with Soviet and American scientists. Since then, many more records have been measured including the longest yet recovered during the European Project for Ice Coring in Antarctica Dome C ice core project, which spans the past 740 000 years. These records provide proof that over the past eight swings between ice ages (glacials) and warm periods similar to today (interglacials), atmospheric CO2 varied between 180 and 280 ppm, demonstrating that today’s CO2 concentration of 400 ppm exceeds the natural variability seen over hundreds of thousands of years.

Over the past decade, new high-resolution ice core records have been used to investigate how quickly CO2 changed in the past. These records come from inland West Antarctica (West Antarctic Ice Sheet Divide Ice Core) and coastal Antarctica, where snow accumulates faster and therefore records have finer time resolution (for example, Law Dome, Talos Dome and Roosevelt Island), and are used for direct comparison with the Mauna Loa record and with global averaged mole fractions. Horizontal ice cores, where very old ice lies exposed near the surface (for example, Taylor Dome and Allan Hills) are also being used to expand the records back in time and to permit large volumes of ice to be sampled for additional measurements, including stable isotopes in CO2, to investigate what sources and sinks caused the changes in CO2 concentration.

Pacing and mechanisms of past carbon dioxide changes

Some 23 000 years ago, Earth emerged from the last ice age as atmospheric CO2 concentrations and temperature began to rise. Between 23 000 and 9 000 years ago, the amount of CO2 in the atmosphere increased by 80 ppm, rising from 180 to 260 ppm. State-of-the-art measurements and analytical techniques show that the increases in CO2 occurred several centuries before the associated temperature changes. The West Antarctica ice core record reveals three distinct types of CO2 variability during this time period:

  •    Slow CO2 increases. CO2 increased slowly at about 10 ppm per 1 000 years between 18 000 and 13 000 years ago. This slow change is thought to be due to the enhanced release and reduced uptake of carbon stored in the deep ocean, caused by changes in ocean temperature and salinity, a reduction in sea ice and biological activity in the Southern Ocean.
  •    Abrupt CO2 increases. Fast CO2 increases of 10–15 ppm over 100–200 years have been seen at three time periods: 16 000, 15 000 and 12 000 years ago. These three periods of rapid change account for almost half of the total CO2 increase during the deglaciation and are linked to sudden changes in ocean circulation patterns, a see-saw tug of war between the North Atlantic and Southern Ocean deep ocean currents, causing a rapid release of carbon to the atmosphere. In comparison, fossil fuel combustion caused CO2 to increase 120 ppm in the last 150 years.
  •     Stable CO2 plateaux. Curiously, each of the rapid events was followed by stable CO2 conditions that lasted about 1 000–1 500 years. While the explanation for these stable conditions is still under debate, plausible causes are further changes in ocean circulation from the melting ice sheets, slow changes in growth of land plants and ocean–atmosphere exchange following the rapid CO2 increases.


Past examples for future commitments

Geological records that predate ice core archives provide an opportunity to learn how the Earth system responded when atmospheric CO2 concentrations were last similar to those recorded today and those expected in the coming decades. Information derived from alkenones, boron isotopes and fossil leaf stomata preserved in layers of rock and sediment provide estimates of CO2 concentrations over the past millions of years. These data help to estimate the sensitivity of the Earth’s environmental systems to CO2 concentrations that were higher than pre-industrial levels and thus help to test and improve climate, ice sheet and Earth system models. Time periods of interest include the mid-Pliocene, 3–5 million years ago, in which the last time Earth’s atmosphere contained 400 ppm CO2. During that period global mean surface temperatures were 2–3 °C warmer than today, ice sheets in Greenland and West Antarctica melted and even parts of East Antarctica’s ice had retreated, causing the sea level to rise 10–20 m higher than today. During the mid-Miocene, some 15 to 17 million years ago, atmospheric CO2 reached 400–650 ppm and global mean surface temperatures were 3–4 °C warmer than those today. During the warmest intervals, East Antarctica’s ice sheets retreated to the continent’s interior, causing the sea level to rise to 40 m. Prior to 34 million years ago, atmospheric CO2 levels were typically  greater than 1 000 ppm. Temperatures were so warm that ice sheets were unable to grow in Antarctica.

These precious data on windows into the past provide useful examples to assess the environmental and ecosystem response to high CO2 concentrations and thus provide invaluable constraints to model projections of the impact of future GHG emission scenarios.

Selected References for Atmospheric CO2 Concentrations Though Time

Bauska, T. K. et al.: Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation, Proceedings of the National Academy of Sciences, 113, 3465-3470, 10.1073/pnas.1513868113, 2016.

Marcott, S. A. et al.: Centennial-scale changes in the global carbon cycle during the last deglaciation, Nature, 514, 616-619, 10.1038/nature13799

Levy, R. et al.: Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene, Proceedings of the National Academy of Sciences 113, 3453-3458, 10.1073/pnas.1516030113, 2016


References for Figure

Martinez-Boti, M. A. et al. Plio-Pleistocene climate sensitivity evaluated using high-resolution CO2 records. Nature 518, 49-54, doi:10.1038/nature14145 (2015).

Foster, G. L., Lear, C. H. & Rae, J. W. B. The evolution of pCO2, ice volume and climate during the middle Miocene. Earth and Planetary Science Letters 341–344, 243-254, doi: (2012).

Greenop, R., Foster, G. L., Wilson, P. A. & Lear, C. H. Middle Miocene climate instability associated with high-amplitude CO2 variability. Paleoceanography 29, 2014PA002653, doi:10.1002/2014pa002653 (2014).

Pearson, P. N., Foster, G. L. & Wade, B. S. Atmospheric carbon dioxide through the Eocene-Oligocene climate transition. Nature 461, 1110-1113 (2009).

Seki, O. et al. Alkenone and boron-based Pliocene pCO2 records. Earth and Planetary Science Letters 292, 201-211 (2010).

Bartoli, G., Hönisch, B. & Zeebe, R. E. Atmospheric CO2 decline during the Pliocene intensification of Northern Hemisphere glaciations. Paleoceanography 26, n/a-n/a, doi:10.1029/2010PA002055 (2011).

Badger, M. P. S. et al. CO2 drawdown following the middle Miocene expansion of the Antarctic Ice Sheet. Paleoceanography 28, 42-53, doi:10.1002/palo.20015 (2013).

Zhang, Y. G., Pagani, M., Liu, Z., Bohaty, S. M. & DeConto, R. A 40-million-year history of atmospheric CO2. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, doi:10.1098/rsta.2013.0096 (2013).

Pagani, M. et al. The Role of Carbon Dioxide During the Onset of Antarctic Glaciation. Science 334, 1261-1264, doi:10.1126/science.1203909 (2011).

Pagani, M., Liu, Z., LaRiviere, J. & Ravelo, A. C. High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations. Nature Geosci 3, 27-30 (2010).

Van der Burgh, J., Visscher, H., Dilcher, D. L. & Kuerschner, W. M. Paleoatmospheric signatures in Neogene fossil leaves. Science 260, 1788-1790 (1993).

Kurschner, W. M., Van der Burgh, J., Visscher, H. & Dilcher, D. L. Oak leaves as biosensors of late Neogene and early Pleistocene paleoatmospheric CO2 concentrations. Marine Micropaleontology 27, 299-312 (1996).

Kürschner, W. M., Kvacek, Z. & Dilcher, D. The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems. Proceedings of the National Academy of Sciences of the United States of America 105, 449-453, doi:10.1073/pnas.0708588105 (2008).

Retallack, G. J. Refining a pedogenic-carbonate CO2 paleobarometer to quantify a middle Miocene greenhouse spike. Palaeogeography, Palaeoclimatology, Palaeoecology 281, 57-65, doi: (2009).

Beerling, D. J., Fox, A. & Anderson, C. W. Quantitative uncertainty analyses of ancient atmospheric CO2 estimates from fossil leaves. American Journal of Science 309, 775-787, doi:10.2475/09.2009.01 (2009).

Royer, D. L., Berner, R. A. & Beerling, D. J. Phanerozoic atmospheric CO2 chnage: evaluating geochemical and paleobiological approaches. Earth-Science Reviews 54, 349-392 (2001).

Doria, G. et al. Declining atmospheric CO2 during the late Middle Eocene climate transition. Am J Sci 311, 63-75, doi:10.2475/01.2011.03 (2011).

McElwain, J. C. Do fossil plants signal palaeoatmospheric carbon dioxide concentration in the geological past? Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, 83-96, doi:10.1098/rstb.1998.0193 (1998).

Smith, R. Y., Greenwood, D. R. & Basinger, J. F. Estimating paleoatmospheric pCO2 during the Early Eocene Climatic Optimum from stomatal frequency of Ginkgo, Okanagan Highlands, British Columbia, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 293, 120-131, doi: (2010).

Greenwood, D. R., Scarr, M. J. & Christophel, D. C. Leaf stomatal frequency in the Australian tropical rainforest tree Neolitsea dealbata (Lauraceae) as a proxy measure of atmospheric pCO2. Palaeogeography, Palaeoclimatology, Palaeoecology 196, 375-393, doi: (2003).

Meinshausen, M. et al. The RCP greenhouse gas concentrations and their extensions from 1765 to 2300. Climatic Change 109, 213-241, doi:10.1007/s10584-011-0156-z (2011).


Carbon Dioxide (CO2)

Carbon dioxide is the single most-important anthropogenic GHG in the atmosphere, contributing ~65% of the radiative forcing by LLGHGs. It is responsible for ~82% of the increase in radiative forcing over the past decade and ~83% over the past 5 years. The pre-industrial level of 278 ppm represented a balance of fluxes among the atmosphere, the oceans and the land biosphere. Atmospheric CO2 reached 145% of the pre-industrial level in 2016, primarily because of emissions from combustion of fossil fuels and from cement production (the total sum of CO2 emissions was 9.9 ± 0.5 PgC in 2015 [8]), deforestation and other land-use change (1.0 ± 0.5 PgC average for 2006–2015). Of the total emissions from human activities during the period 2006–2015, about 44% accumulated in the atmosphere, 26% in the ocean and 30% on land [8]. The portion of CO2 emitted by fossil fuel combustion that remains in the atmosphere (airborne fraction) varies inter-annually due to the high natural variability of CO2 sinks without a confirmed global trend.

CO2 mole fraction
CO2 growth rate
Figure 3. Figure 3. Globally averaged CO2 mole fraction (a) and its growth rate (b) from 1984 to 2016. Increases in successive annual means are shown as the shaded columns in (b). The red line in (a) is the monthly mean mole fraction with the seasonal variations removed; the blue dots and line depict the monthly averages.

The globally averaged CO2 mole fraction in 2016 was 403.3 ± 0.1 ppm (Figure 3). The record increase in the annual mean from 2015 to 2016 (3.3 ppm) is larger than the previous record increase from 2012 to 2013 and 50% above the average growth rate for the past decade (~2.2 ppm per year). The higher growth rate in 2016 and 2015, in comparison with previous years, is due, in part, to the increased natural emissions of CO2 related to the most-recent El Niño event, as explained in the previous (twelfth) edition of this GHG bulletin.


The “other” CO2 problem – Ocean acidification

Profound changes in seawater chemistry are underway as the ocean takes up about one fourth of the anthropogenic CO2 emitted to the atmosphere year-on-year. This phenomenon, known as ocean acidification, has emerged as a key issue of global concern in the last fifteen years. Some facts about ocean acidifications can be found in “20 Facts about ocean acidification”.The Ocean Acidification International Coordination Centre (OA-ICC) works to promote, facilitate and communicate global activities on ocean acidification. 

At the “Surface Ocean CO2 Variability and Vulnerability” (SOCOVV) workshop at UNESCO, Paris in April 2007, participants agreed to establish a global surface CO2 data set that would bring together, in a common format, all publicly available fCO2 data for the surface oceans. This work allowed to map the distribution of fCO2 in Surface Ocean CO2 Atlas (SOCAT,, which includes: 

- a 2nd level quality controlled global surface ocean fCO2  data set following agreed procedures and regional review,

- and a gridded SOCAT product of monthly surface water fCO2 means on a 1° x 1° grid with no temporal or spatial interpolation.

EXAMPLE: SOCAT product for January

SACAT product January


Methane (CH4)

Methane contributes ~17% of the radiative forcing by LLGHGs. Approximately 40% of CH4 is emitted into the atmosphere by natural sources (for example, wetlands and termites), and ~60% comes from anthropogenic sources (for example, ruminants, rice agriculture, fossil fuel exploitation, landfills and biomass burning). Atmospheric CH4 reached 257% of the pre-industrial level (~722 ppb) in 2016 due to increased emissions from anthropogenic sources. Globally averaged CH4 calculated from in situ observations reached a new high of 1853 ± 2 ppb in 2016, an increase of 9 ppb with respect to the previous year (Figure 4). The mean annual increase of CH4 decreased from ~13 ppb per year during the early 1980s to near zero during the period 1999–2006. Since 2007, atmospheric CH4 has been increasing again. Studies using GAW CH4 measurements indicate that increased CH4 emissions from wetlands in the tropics and from anthropogenic sources at mid-latitudes of the northern hemisphere are likely causes.

CH4 mole fraction
CH4 growth rate
Figure 4.Globally averaged CH4 mole fraction (a) and its growth rate (b) from 1984 to 2016. Increases in
successive annual means are shown as the shaded columns in (b). The red line in (a) is the monthly mean mole fraction with the seasonal variations removed; the blue dots and line depict the monthly averages.



Nitrous Oxide (N2O)

N2O mole fraction N2O growth rate
Figure 5. Globally averaged N2O mole fraction (a) and its growth rate (b) from 1984 to 2016. Increases in successive annual means are shown as the shaded columns in (b). The red line in (a) is the monthly mean mole fraction with the seasonal variations removed; in this plot, it overlaps with the blue dots and line that depict the monthly averages.

Nitrous oxide contributes ~6% of the radiative forcing by LLGHGs. It is the third most-important individual contributor to the combined forcing. It is emitted into the atmosphere from both natural (~60%) and anthropogenic sources (~40%), including oceans, soils, biomass burning, fertilizer use and various industrial processes. The globally averaged N2O mole fraction in 2016 reached 328.9 ± 0.1 ppb, whichis 0.8 ppb above the previous year (Figure 5) and 122% of the pre-industrial level (270 ppb). The annual increase from 2015 to 2016 is slightly lower than the mean growth rate over the past 10 years (0.9 ppb per year). The likely causes of N2O increase in the atmosphere are an increased use of fertilizers in agriculture and an increased release of N2O from soils due to an excess of atmospheric nitrogen deposition related to air pollution.


Other greenhouse gases

Sulphur hexafluoride (SF6) is a potent LLGHG. It is produced
by the chemical industry, mainly as an electrical insulator in
power distribution equipment. Its current mole fraction is
about twice the level observed in the mid-1990s (Figure 6(a)).

Stratospheric ozone-depleting chlorofluorocarbons (CFCs),
together with minor halogenated gases, contribute ~11% of the radiative forcing by LLGHGs. While CFCs and most halons are decreasing, some hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), which are also potent GHGs, are increasing at relatively rapid rates, although they are still low in abundance (at ppt(6) levels).

SF6 mole fraction

halocarbons mole fraction

Figure 6.Monthly mean mole fractions of sulphur hexafluoride (SF6) and the most important halocarbons: SF6 and lower mole fractions of halocarbons (a) and higher ones of halocarbons (b).

 This bulletin primarily addresses LLGHGs. Relatively shortlived tropospheric ozone has a radiative forcing comparable to that of halocarbons. Many other pollutants, such as carbon monoxide, nitrogen oxides and volatile organic compounds (VOCs), although not referred to as GHGs, have small direct or indirect effects on radiative forcing. Aerosols (suspended particulate matter) are short-lived substances that alter the radiation budget. All gases mentioned herein, as well as aerosols, are included in the observational programme of GAW, with support from WMO Members and contributing networks.

Acknowledgements and links

Fifty-one WMO Members have contributed CO2 and other GHG data to GAW WDCGG. Approximately 46%
of the measurement records submitted to WDCGG were obtained at sites of the NOAA Earth System Research
Laboratory cooperative air-sampling network. For other networks and stations, see GAW Report No. 229. The
Advanced Global Atmospheric Gases Experiment also contributed observations to this bulletin. Furthermore,
the GAW observational stations that contributed data to this bulletin, shown in Figure 2, are included in the list of contributors on the WDCGG website ( They are also described in the GAW Station Information System ( supported by MeteoSwiss, Switzerland. 


[1] National Oceanic & Atmospheric Administration Earth System Research Laboratory, 2016: Trends in atmospheric carbon dioxide,

[2] World Meteorological Organization, 2016: WMO statement on the state of the global climate,

[3] Butler, J.H. and S.A. Montzka, 2016: The NOAA annual greenhouse gas index (AGGI),

[4] National Oceanic & Atmospheric Administration Earth System Research Laboratory, 2016: NOAA’s Annual Greenhouse Gas Index,

[5] Intergovernmental Panel on Climate Change (IPCC), 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (R.K. Pachauri and L.A. Meyer, eds.). Geneva, IPCC.

[6] World Meteorological Organization, 2009: Technical Report of Global Analysis Method for Major Greenhouse Gases by the World Data Center for Greenhouse Gases (Y. Tsutsumi, K. Mori, T. Hirahara, M. Ikegami and T.J. Conway). GAW Report No. 184 (WMO/TD-No. 1473), Geneva,

[7] Conway, T.J., P.P. Tans, L.S. Waterman, K.W. Thoning, D.R. Kitzis, K.A. Masarie and N. Zhang, 1994: Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network. Journal of Geophysical Research, 99:22831–22855.

[8] Le Quéré, C. et al., 2016: Global Carbon Budget 2016, Earth System Science Data 8,605-649,


Terms used in this Bulletin are explained in the glossary.










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