Indicator Assessment

Atmospheric greenhouse gas concentrations

Indicator Assessment
Prod-ID: IND-2-en
  Also known as: CSI 013 , CLIM 052
Published 25 Jan 2012 Last modified 11 May 2021
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  • The global average concentrations of various greenhouse gases in the atmosphere have reached the highest levels ever recorded, and concentrations continue to increase. The combustion of fossil fuels from human activities and land-use changes are largely responsible for this increase.
  • The concentration of all GHGs, including cooling aerosols that are relevant in the context of the 2oC temperature target, reached a value of 399 ppm CO2 equivalents in 2009. 
  • The concentration in 2009 of the six greenhouse gases (GHG) included in the Kyoto Protocol has reached 439 ppm CO2 equivalent,  an increase of 160 ppm (around +58%) compared to pre-industrial levels. 
  • The concentration of CO2, the most important greenhouse gas, reached a level of 386 ppm by 2009, and further increased to 389 ppm in 2010. This is an increase of approximately 110 ppm (around +39%) compared to pre-industrial levels.


Contribution of the different GHGs as included in the Kyoto and Montreal protocol to the overall greenhouse gas concentration in 1950, 1990 and 2009

Note: The size of the pies depicts the size of the relative increase in GHG concentration

Data source:

Atmospheric concentration of CO2 (ppm)

Note: The figure shows the atmospheric concentration of CO2

Data source:

Atmospheric concentration of CH4 (ppb)

Note: The figure shows the atmospheric concentration of CH4

Data source:

Atmospheric concentration of N2O (ppb)

Note: The concentrations of the individual GHGs under the Kyoto protocol have reached new highs in 2009 The figure shows the atmospheric concentration of N2O

Data source:

Greenhouse gases (GHG) can intercept solar radiation and in such a way affect the climate system. In order to control the emissions of such gases, many of them are included within different international agreements, including the UNEP Montreal Protocol on Substances that deplete the Ozone layer (1987) and the Kyoto Protocol to the UNFCCC which aims to limit global warming (1997)).

  • GHG in the Kyoto Protocol are: Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and three fluorinated gasses (HFC, PFC, SF6)
  • GHG in the Montreal Protocol are three other groups of fluorinated gases: CFCs, HCFCs and CH3CCl3
  • In addition, GHG exist that are not included in global treaties, here called non-protocol gases (NPG), including stratospheric and tropospheric ozone (O3), aerosols such as black carbon, and water vapour. 

The concentration of greenhouse gases (GHG) in the atmosphere has increased during the 20th century, extremely likely [1] caused mainly by human activities related to the use of fossil fuels (e.g. for electric power generation), agricultural activities and land-use change (mainly deforestation) (IPCC, 2007a). The increase of all GHG gases has been particularly rapid since 1950. The first 50 ppm increase above the pre-industrial value of carbon dioxide (CO2), the most important human greenhouse gas, was reached in the 1970s more than 200 years since pre-industrial times (i.e. before 1750), whereas the second 50 ppm increase occurred after just approximately  30 years.

Six GHGs are included in the Kyoto Protocol. Their overall concentration in the atmosphere has reached 439 ppm CO2-equivalent in 2009, an increase of about 160 ppm compared to pre-industrial times (Figure 1). Changes in atmospheric CO2 contributed by far most of the increase (about 67% of the increase from pre-industrial period). When translating the overall 450 ppm CO2-equivalent limit into a limit just for the Kyoto gases only, this means only a further 45 ppm CO2-equivalent increase is possible (with an uncertainty range of  0 – 94 ppm CO2-equivalent).

To evaluate the GHG concentration in the atmosphere in relation to temperature change, it is important to consider all greenhouse gases, i.e. the long-living GHGs under the Kyoto Protocol, those under the Montreal Protocol (direct and indirect), as well as ozone, water vapour and aerosols (IPCC, 2007a). Considering these gases, the total CO2-equivalent concentration reached a level of 399 ppm CO2 eq. in 2009 [2] (Figure 2). The annual concentration increase over recent years has been considerably lower than for earlier years due to the economic crisis (from around 2.3 ppm CO2 eq.yr-1 between 2000 and 2005 to 1.1 ppm CO2 eq.yr-1 in 2009). 

The contribution of tropospheric ozone to the climate system is considered to be stable in the recent decades given its large annual and spatial variation (IPCC, 2007a). Long-term data series on tropospheric ozone are difficult to develop due to the scarcity of representative observing sites with long records and the large spatial heterogeneity (IPCC, 2007a). Overall, assuming a concentration threshold of 450 ppm CO2 equivalents may result in a 2oC temperature change means concentrations can only further increase by about 50 ppm before this threshold value is exceeded. Assuming the 2000-2009 trend of annual increase of total GHG concentrations will also continue in the coming years, the threshold value may be exceeded in less than 25 years. The lower band of the uncertainty range may be exceeded already within the next few years, whereas it may take more than 50 years before the upper uncertainty band is exceeded.

Excluding water vapour, ozone and aerosols, the total concentration of the remaining, long-lived GHGs has increased from 278 in pre-industrial times to 461 ppm CO2 equivalents in 2009. This is about 183 ppm higher than pre-industrial levels. That this concentration is higher than when all gases are considered is caused by the overall cooling effect of aerosols - although certain aerosols act in an opposite manner by enhancing the warming. Overall, aerosols are compensating for around 45% of the current warming induced by the Kyoto and Montreal GHGs. Aerosols have a relatively short lifetime. Due to the overall cooling effect of aerosols, the additional space for long-living GHGs such as CO2 will become smaller before exceeding 450 ppm CO2 equivalents when the aerosol concentrations will continue to decrease, for example as result of non-climate related policy measures. The Montreal Protocol gases contributed as a group about 10% to the current warming (Figure 3). The concentrations of these gases have peaked around the millennium change and have now started to decline due to natural removal processes (IPCC, 2007a).

The concentrations of the individual GHGs under the Kyoto protocol have reached new levels in 2009 (Figure 4,5 and 6). The CO2 concentration reached a level of 386 ppm in that year, and increased further in 2010 to 389 ppm (Figure 4). This is an increase of about 110 ppm (+38%) compared to the pre-industrial levels (i.e. before 1750) (NOAA, 2011). The present CO2 concentration has not been exceeded during the past 420 000 years and possibly not even during the past 20 million years (IPCC, 2007a). The concentration of methane (CH4) has increased to 1793 parts per billion (ppb) in 2009 (+156% from pre-industrial levels), a value which also has not been exceeded during the past 420 000 years (Figure 5). After nearly a decade of no growth or even decrease, the atmospheric CH4 has increased during the past three years. The reasons for this renewed growth are not fully understood, but human-induced sources such as growing industrialisation in Asia, increasing wetland emissions due to land-use changes, biomass burning, as well as increases from natural sources from northern latitudes and the tropics (e.g. CH4 releases from thawing permafrost) (Dlugokencky et al., 2009; Mascarelli, 2009; Shakhova et al, 2010) are considered potential causes (WMO, 2010). The nitrous oxide (N2O) concentration in 2009 was 322 ppm (Figure 6), up 0.6 ppb from the year before and 19% above the pre-industrial level. This concentration has not been exceeded during at least the past 1 000 years.  The concentrations of the F-gases within the scope of the Kyoto Protocol (HFCs, PFCs and SF6) have increased by large factors (between 1.3 and 6.4, depending on the gas) between 1999 and 2009. These gases are very effective absorbers of radiation and even small amounts can significantly affect the climate system. Their contribution to the total climate forcing is rapidly increasing in the past years.

[1] Defined as >95% probability (IPCC, 2007)

[2] More recent data are not available for the annual-average concentration except for CO2, for which data for 2010 are available

Supporting information

Indicator definition

The indicator shows the observed trends of greenhouse gas concentrations. The various greenhouse gases have been grouped in three different ways (see 'Justification for Indicator Selection’ section above). Next to the concentration of individual GHGs, greenhouse gasses are grouped in two ways, using the CO2-equivalent concentration as a way to add the different gasses. The CO2-equivalent concentration of a gas is the CO2 concentration that would cause the same amount of radiative forcing as the mixture of all GHGs. Global annual averages are considered, because in general the gases mix quite well in the atmosphere. 


Atmospheric concentration in parts per million in CO2-equivalent (ppm CO2-eq.).


Policy context and targets

Context description

GHG concentrations is a key indicator relevant to  international climate negotiations as the overall objective of the United Nations Framework Convention on Climate Change (UNFCCC), is ‘to stabilize atmospheric greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system’ (UNFCCC, 1993). Both at the global (UNFCCC, 2009) and the EU level (October 2008 Environment Council conclusions) this ‘dangerous anthropogenic interference’ has been recognised by formulating the objective of keeping the long-term global average temperature rise below 2°C compared to pre-industrial times. Studies have assessed the probability of keeping the long-term temperature rise below this 2°C target in relation to different stabilization levels of GHGs in the atmosphere (Meinshausen, 2006; den Elzen et al., 2007; Van Vuuren et al., 2008). These studies showed that to have a 50% probability of limiting the global mean temperature increase to 2 °C (above pre-industrial levels), the concentration of all GHGs in the atmosphere would need to be stabilised below about 450 ppm CO2  equivalent (range 400-500 ppm CO2 eq.). This includes ozone, water vapour and aerosols. For CO2 only, the 50% probability concentration threshold is around 400 ppm, and for all Kyoto gases about 480 ppm CO2 equivalent (range 432 – 532 ppm CO2  eq. ). Note that the value for the Kyoto gases only, is higher than when considering all GHGs, due to the cooling affect of aerosols (currently about 1.2 W.m-2 or about 70 ppm CO2 eq.). According to the scientific literature the probability of staying below the 2oC becomes very low when stabilization at 550 ppm CO2 eq, ranging between 0% and 37%, considering all GHGs.


The ultimate objective of the United Nations Framework Convention on Climate Change (UNFCCC) is to achieve 'stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner'.

To reach the UNFCCC objective, the EU has specified more quantitative targets in its 6th environmental action programme (6th EAP) which mentions a long-term EU climate change objective of limiting global temperature rise to a maximum of 2oC compared with pre-industrial levels. This target was confirmed by the Environment Councils of 20 December 2004 and 22-23 March 2005. Scientific insight shows that in order to have a high chance of meeting the EU policy target of limiting global temperature rise to 2oC above pre-industrial levels, global GHG concentrations may need to be stabilised at much lower levels, e.g. 450 ppm CO2-equivalent. Stabilisation of concentrations at well below 550 ppm CO2-equivalent may be needed and global GHG emissions would have to peak within two decades, followed by substantial reductions by 2050 compared with 1990 levels.

The EU Environment Council (October 2008) adopted the conclusion that to achieve stabilisation in an equitable manner, developed countries should reduce emissions by about 15-30% by 2020 and 80-95% by 2050, below the base year levels (1990).

The Copenhagen Accord (Dec. 2009) recognised the objective of keeping the maximum global average temperature rise below 2 °C, although without specifying the base year or period, and the need for a review in 2015 to consider a possible goal of limiting temperature rise to 1.5 °C using new scientific insights.

Related policy documents

  • Council Decision (2002/358/EC) of 25 April 2002
    Council Decision (2002/358/EC) of 25 April 2002 concerning the approval, on behalf of the European Community, of the Kyoto Protocol to the United Nations Framework Convention on Climate Change and the joint fulfilment of commitments thereunder.
  • Greenhouse gas monitoring mechanism Decision
    Decision No 280/2004/EC of the European Parliament and of the Council of 11 February 2004 concerning a mechanism for monitoring Community greenhouse gas emissions and for implementing the Kyoto Protocol


Methodology for indicator calculation

For atmospheric CO2, the global average values are directly taken from NOAA (NOAA, 2011, see also Global average concentration values for the other gases are mainly based on CDIAC numbers (2011) (see . Radiative forcings are calculated with approximate equation according to (IPCC, 2001; IPCC, 2007a), based on the observed atmospheric concentrations and using radiative efficiencies for CO2, CH4, and N2O based on IPCC (2007a), and according toWMO (2002) for other gases. The equations used to compute the contribution of the individual gases are presented below: 


Trace gas

Parameterisation, Radiative forcing, change in F (Wm-2)



change in F = alpha ln (C/C0)

C and C0 are the current and pre-industrial concentrations (ppm) of CO2, respectively

alpha = 5.35


change in F = alpha (sq. root of M - sq. root of M0 ) - (f (M,N0) - f (M0,N0))


f (M,N)= 0.47 ln [1+2.01*10-5 (MN)0.75 + 5.31*10-15 M(MN)1.52]

M and M0 are the current and pre-industrial concentrations (ppb) of CH4, respectively; N and N0 are the current and pre-industrial concentrations (ppb) of N2O, respectively.

alpha  = 0.036


change in F = alpha (sq. root of N - sq. root of N0 ) - (f (M0,N) - f (M0,N0))




f (M,N)= 0.47 ln [1+2.01*10-5 (MN)0.75 + 5.31*10-15 M(MN)1.52]

M and M0 are the current and pre-industrial concentrations of CH4, respectively; N and N0 are the current and pre-industrial concentrations of N2O, respectively.

alpha  = 0.12


change in F = alpha (X-X0)

 X and X0 are the current and pre-industrial concentrations (ppb) of gas X, respectively.

Values for alpha depend on molecule, and are taken from WMO, 2002.

In order to calculate the concentration of all long-living Greenhouse Gases also the Montreal Gases (i.e. CFCs & HCFCs) need to be included. A similar approach is applied for these gases:


change in F = alpha (X-X0)

 X and X0 are the current and pre-industrial concentrations (ppb) of gas X, respectively.

Values for alpha depending on molecule (see below), taken from WMO, 2002.

Overview of used alpha values for chlorine Kyoto and Montral Gases 

Kyoto gases

Montreal gases



















































In calculating the radiative forcing (and accompanying concentration levels) of the Montreal Protocol gases, the effect of ozone depleting substances on the stratospheric ozone layer was also considered. Velders et al (2007) estimated that the observed changes in stratospheric ozone between 2000 and 2010 contributed a forcing of -0.06 W.m2 (or about 10 ppm ppm CO2 eq.). To quantify the concentration of all greenhouse gases, important in relation to the 2oC target, the forcing of ozone, water vapor in the atmosphere and aerosols have been added. Due to uncertainties in the measurements and the large inter-annual and seasonal variation, the forcing is kept constant over the years for ozone and water vapour (IPCC, 2007a). These values are 0.35 and 0.07 W.m-2 for ozone and water vapor, respectively (IPCC, 2007a, pg 204). For aerosols a constant value of -1.2 W.m2 was used back to 2000. Between 1990 and 2000 2% higher values were assumed, and between 1970 and 1990 10% higher values (back to 1.35 W.m2 in 1970) (Bollen et al, 2009). For all three representations of the GHG concentration (i.e. Kyoto gasses only, all long-living GHG and all Greenhouse gases including zone and aerosols), the following approach has been used, adding the different climate forcing:


Ceq = C0 exp ((SUM change in F) / alpha)

Ceq is the current CO2-equivalent concentration; C is the pre-industrial CO2 concentration. Summation is over radiative forcings of all greenhouse gases considered.

alpha  = 5.35

Methodology for gap filling

If measurements from a station are missing for a certain year, the global trend is derived from available stations data. 

Methodology references

  • NOAA (2011) (used for CO2 data)
  • CDIAC (2011a) for CFC-113 HCFC-22, HCFC-141b, HCFC-142b HFC-125, HFC-134a, HFC-152a, HFC-365mfc, HFC-23 Halon-1211, Halon-1301 CH3Cl, CH2Cl2, CHCl3, CH3Br CH3CCl3, CHClCCl2, CCl2CCl2 SF6, SO2F2 PFC-14, PFC-116, PFC-218 HFC-227ea HFC-236fa HFC-245fa
  • CDIAC (2011b) for CH 4 , N 2 O, CO, H 2 , CFC-11, CFC-12, CH3CCl3, CCl4, CFC-113, and CHCl3. 
  • IPCC (2001) Climate Change 2001: The Physical Science Basis.  (eds.) J. T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P. J. van der Linden and D. Xiaosu. Working Group 1 Contribution to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Appendix II.3.11 on GHG forcing)
  • IPCC (2007a) Climate Change 2007: The Physical Science Basis.  (eds.) Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt K, Tignor MMB & Miller HL,. Working Group 1 Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). Technical Summary and Chapter 10 (Global Climate Projections)
  • WMO (2002) Scientific Assessment of Ozone Depletion: 2002, Global Ozone Research and Monitoring Project–Report No. 47, World Meteorological Organization), Geneva, Switzerland
  • WMO (2011a) Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project–Report 52, World Meteorological Organization),Geneva, Switzerland
  • Butler (2009) The NOAA annual greenhouse gas index (AGGI). Update September 2009.
  • Velders et al. (2009) Velders, G. J.M.; S.O. Andersen, J. S. Daniel, D. W. Fahey & M. McFarland (2007)The Importance of the Montreal Protocol in Protecting Climate, PNAS 104:4814 – 4819
  • Bollen et al. (2009) Bollen, J.C, C.J. Brink, H.C. Eerens & A.J.G. Manders (2009) Co-benefits of climate change mitigation policies: literature review and new results. Report 500116005 PBL Netherlands Environmental Assessment Agency, 72 pg. 
  • WMO (2011b) Greenhouse Gas Bulletin: The State ofGreenhouseGases in the Atmosphere Based on Global Observations through 2010


Methodology uncertainty

Global average concentrations since approximately 1980 are determined by averaging measurements from several ground-station networks (SIO, NOAA/CMDL,ALE/GAGE/AGAGE), each consisting of several stations distributed across the globe.

Absolute accuracies of global annual average concentrations are of the order of 1 % for CO2, CH4 and N2O, and CFCs; for HFCs, PFCs, and SF6, absolute accuracies can be up to 10-20 %. However, the year-to- year variations are much more accurate. Radiative forcing calculations have an absolute accuracy of 10% (IPCC, 2001); trends in radiative forcing are much more accurate.

The dominant sources of error for radiative forcing are the uncertainties in modelling radiative transfer in the Earths atmosphere and in the spectroscopic parameters of the molecules involved. Radiative forcing is calculated using parameterisations that relate the measured concentrations of greenhouse gases to radiative forcing. The overall uncertainty in radiative forcing calculations (all species together) is estimated to be 10 % (IPCC, 2001). Radiative forcing is also expressed as CO2-equivalent concentration; both have the same uncertainty. The uncertainty in the trend in radiative forcing/CO2-equivalent concentration is determined by the precision of the method rather than the absolute uncertainty discussed above. The uncertainty in the trend is therefore much less than 10 %, and is determined by the precision of concentration measurements (0.1 %).

It is important to note that global warming potentials are not used to calculate radiative forcing. They are used only to compare the time-integrated climate effects of emissions of different greenhouse gases.

Data sets uncertainty

Direct measurements have good comparability. Although methods for calculating radiative forcing and CO2-equivalent are expected to improve further, any update of these methods will be applied to the complete dataset covering all years, so this will not affect the comparability of the indicator over time.

Rationale uncertainty

Atmospheric concentrations of greenhouse gases are a well-established indicator of changes in atmospheric composition, which causes changes of the global climate system. Here we only present observed trends, having lower uncertainties than model projections. 

Data sources

Other info

DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 013
  • CLIM 052
Frequency of updates
Updates are scheduled once per year
EEA Contact Info


Geographic coverage

Temporal coverage



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