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Atmospheric greenhouse gas concentrations (CSI 013) - Assessment published Nov 2010

Indicator Assessment Created 19 Aug 2010 Published 08 Nov 2010 Last modified 11 Sep 2012, 04:51 PM
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Generic metadata


Climate change Climate change (Primary topic)

soer2010 | csi | climate change | greenhouse gases | thematic assessments | kyoto protocol | understanding climate change
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 013
Temporal coverage:
Geographic coverage:
Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom

Indicator definition

The indicator shows the observed trends of greenhouse gas concentrations. The various greenhouse gases have been grouped in three different ways (see rationale). Except for the concentration of individual GHGs, the effect on the enhanced greenhouse effect is presented as CO2-equivalent concentrations, which 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.).

Key policy question: What is the trend in greenhouse gas concentration in the atmosphere? Will it remain below 450 ppm CO2-equivalent giving a 50% probability that the global temperature rise will not exceed 2 degrees Celsius above pre-industrial levels?

Key messages


  • The global average concentrations of various greenhouse gasses in the atmosphere reached their highest levels ever recorded, and continue increasing. The combustion of fossil fuels from human activities and land-use changes are largely responsible for this increase.
  • The concentration in 2008 of the six greenhouse gases (GHG) included in the Kyoto Protocol has reached 438 ppm CO2 equivalent, which is an increase of 160 ppm compared to the pre-industrial level. Considering all GHGs (incl. ozone and various cooling aerosols), the concentration has reached a value of 399 ppm CO2 equivalents in 2008, which is 121 ppm higher than in pre-industrial times. The concentration of CO2 -the most important greenhouse gas- has reached in 2008 a level of 385 ppm, and in 2009 387 ppm. This is an increase of nearly 110 ppm compared to the pre-industrial level.
  • Without climate policy, the overall concentration of the six Kyoto gasses is projected to increase up to 638-1360 ppm CO2 -equivalent by 2100, whereas the concentration of all GHGs may increase up to 608-1535 ppm CO2 -equivalent.  The global atmospheric GHG concentration of 450 ppm CO2-equivalent could already become exceeded up 2015 (depending on climate policy and definitions)

    Measured and projected concentration of all greenhouse gases (left) and Kyoto greenhouse gases (right)

    Note: Graphs show observed and projected green house gases. Projections are made using all main IPCC SRES scenarios

    Data source:


    Downloads and more info

    Key assessment

    The concentration of greenhouse gases (GHG) in the atmosphere has increased during the 20th century, extremely likely*  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). The increase of all GHG gasses has been particularly rapid since 1950. The first 50 ppm increase above the pre-industrial value of carbon dioxide (CO2) for example, was reached in the 1970s after more than 200 years, whereas the second 50 ppm was achieved in about 30 years. In the recent 10 years the highest average growth rate has been recorded for any decade since atmospheric CO2 measurements began (IPCC, 2007). This increase was nearly entirely caused by human activities (of which about two third caused by fossil fuel use and one third by land-use change/deforestation) (IPCC, 2007). The CO2-equivalent concentration of the six greenhouse gases included in the Kyoto Protocol (i.e. CO2, CH4, N2O, HFC, PFC, SF6) reached 438 ppm CO2-equivalent in 2008, an increase of 160 ppm from the pre-industrial level. According to the NOAA Annual Greenhouse Gas Index (AGGI), the total radiative forcing by all long-lived greenhouse gases (carbon dioxide (CO2), methane (CO4), nitrous oxide (N2O), CFC-12, CFC-11, and various lesser gases) has increased by 26% since 1990. CO2 contributed about 64% to the overall global radiative forcing from the pre-industrial period, and 85% to the increase in radiative forcing over the past decade (NOAA, 2009). Considering all long living greenhouse gasses (i.e. the Kyoto Gasses plus the CFCs & HCFCs, that are included in the Montreal Protocol), a level of 466 ppm CO2-equivalents has been reached in 2008. Adding, finally, ozone and various aerosols, the GHG concentration has reached a level of 399 ppm CO2 equivalents in 2008. Thus, aerosols are important for the global climate, since they have in general a strong cooling affect - although some aerosols enhance the warming. In total aerosols are compensating for about 70% of the climate forcing by CO2. Note that these aerosols have a relative short lifetime, the emissions will be reduced due to non-climate related policy measures and as such their importance for the future climate will diminish. Likewise, the Montreal Protocol gases (CFCs, HCFCs, and CH3CCl3) as a group still contributed significantly (about 17%) to the current warming. Also their contribution is likely to decrease in the near-term future due to policy measures (IPCC, 2007a).

    Assessing the role of the individual greenhouse gasses, concentrations up to 2008 of CO2, methane (CH4) and nitrous oxide (N2O) have increased by 38%, 156%, and 15%, respectively, compared with the pre-industrial era (before 1750). The CO2 concentration –the most important greenhouse gas- has reached in 2008 a level of 385 ppm, and in 2009 386 ppm (=39%). This is an increase of nearly 110 ppm compared to the pre-industrial level (  The present CO2 concentration has not been exceeded during the past 420 000 years and may be even not even during the past 20 million years. The CO2 increase is nearly entirely caused by human activities (of which about 2/3 caused by fossil fuel use, 1/3 due to land-use change). Humans are also directly responsible for about two third (mainly fossil fuel exploitation, rice agriculture, biomass burning, landfills) and one third (as fuel combustion, biomass burning, fertilizer use and some industrial processes) of the increase in CH4 and N2O, respectively. The concentration of CH4 has increased up to 1790 part per billion (ppb), a value have also not been exceeded during the past 420 000 years. The increase (0.4% both in 2007 and 2008, WMO, 2009) is remarkable after nearly a decade with no increase or even decrease. Next to growing industrialization in Asia, rising wetland emissions due to land-use changes, and biomass burning, a cause could be CH4 releases from thawing permafrost (Dlugokencky etla, 2009; Mascarelli, 2009; Shakhova et al, 2010). The present N2O concentration (now 322 ppb, plus 1 ppb compared to 2007) has not been exceeded during at least the past 1 000 years. The fluorine-containing Kyoto Protocol gases (HFCs, PFCs and SF6) are very effective absorbers of radiation and as such even small amounts can affect significantly the climate system. Their concentrations have increased by large factors (between 1.3 and 6.4, depending on the gas) between 1998 and 2008. As such their role in the total climate forcing is rapidly increasing in the past years. Concentrations of different Montreal Protocol gases (i.e. CFCs, HCFCs, and CH3CCl3) have peaked around the millennium change and have are started to decline due to natural removal processes (IPCC, 2007a). Finally, the concentration of stratospheric ozone became stable (thus the contribution to the climate system is decreasing) in the recent decades, whereas assessments of long-term trends in tropospheric ozone are difficult due to the scarcity of representative observing sites with long records and the large spatial heterogeneity (IPCC, 2007a).

    The IPCC (2001, 2007a) showed various projected future greenhouse gas concentrations for the 21st century, varying due to a range of scenarios of socio-economic, technological and demographic developments (Figure 1, Table 1). These SRES scenarios assume no implementation of specific climate-driven policy measures. Under these scenarios, the overall concentration of the six Kyoto gasses is projected to increase up to 638-1360 ppm CO2-equivalent by 2100, whereas the concentration of all GHGs (incl. aerosols) may increase up to 608-1535 ppm CO2-equivalent by 2100 (Fig. 1). Note the importance of the non-Kyoto gasses (especially aerosols) is projected to strongly decrease, resulting in decreasing differences between only-Kyoto and all-GHG projections, with the exception of the A1FI scenario (where especially Montreal gasses and ozone remain high).  

    Given these SRES projections without climate policy, a global atmospheric GHG concentration of 450 ppm CO2- equivalent may become exceeded between 2010-2015 (in case of Kyoto gasses only) or between 2020-2030 (all GHGs). A level of 550 ppm CO2-equivalent may become exceeded a decade later (Figure 1). Stringent climate policies, leading to substantial global emission reductions, are needed to remain below these targets or return back to these levels after an overshoot. Although uncertain, if such policies would become implemented –in combination with moderate baseline emissions- this could lead to a  peak at 455 ppm  CO2-equiv. around 2050, followed by a decline down to about 427 ppm CO2 equivalent  in 2100 (Moss et al, 2010, Table 1) (considering all gasses).

    [1] 2009 concentration levels are yet not available for the other greenhouse gasses.

    * Defined as >95% probability (IPCC, 2007a)

    Table 1: Projected changes in atmospheric GHG concentration (considering either Kyoto gasses only or all GHGs)















    Kyoto only




































    all GHGs









    (incl. aerosols)



















    Source: IPCC, 2001, 2007a for the SRES scenarios; Moss et al, 2010 & Van Vuuren pers. Comm.. for the RCP scenario

      1This RCP2.6 scenario assumes stringent climate policy and a moderate socio-economic development

      22009 concentration levels are yet not available for the other greenhouse gasses. 

    Data sources

    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 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 (2011).

    Global average concentration values for the other gasses are mainly based on CDIAC (2011). 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 to WMO (2002) for the other gases. Slightly updated values became available for some substances (WMO, 2011a). However, too late for this assessment. Updates will be included in a next version. The equations used to compute the contribution of the individual gasses 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

    HFC, PFC & SF6

    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 Gasses also the Montreal Gasses (i.e. CFCs & HCFCs) need to be included. A similar approach is applied for these gasses


    CFCs & HCFCs

    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 Gasses

    Kyoto gasses

    Montreal gasses




















































    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 gasses 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

    No methodology references available.


    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. 

    More information about this indicator

    See this indicator specification for more details.

    Contacts and ownership

    EEA Contact Info

    Blaz Kurnik


    EEA Management Plan

    2010 2.0.1 (note: EEA internal system)


    Frequency of updates

    Updates are scheduled once per year
    European Environment Agency (EEA)
    Kongens Nytorv 6
    1050 Copenhagen K
    Phone: +45 3336 7100