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You are here: Home / Data and maps / Indicators / Atmospheric greenhouse gas concentrations / Atmospheric greenhouse gas concentrations (CSI 013) - Assessment published Oct 2005

Atmospheric greenhouse gas concentrations (CSI 013) - Assessment published Oct 2005

Indicator Assessment Created 17 May 2005 Published 06 Oct 2005 Last modified 11 Sep 2012, 04:51 PM
Topics: ,
 
Contents
 

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.

Units

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 atmospheric concentration of carbon dioxide (CO2), the main greenhouse gas, has increased by 34 % compared with pre-industrial levels as a result of human activities, with an accelerated rise since 1950. Other greenhouse gas concentrations have also risen as a result of human activities. The present concentrations of CO2 and CH4 have not been exceeded during the past 420 000 years and the present N2O concentration during at least the past 1 000 years.

IPCC (2001) baseline projections show that greenhouse gas concentrations are likely to exceed the level of 550 ppm CO2-equivalent in the next few decades (before 2050).

Measured and projected concentrations of 'Kyoto' greenhouse gases

Note: N/A

Data source:

SIO; ALE/GAGE/AGAGE; NOAA/CMDL; IPCC, 2001

Downloads and more info

Key assessment

The concentration of greenhouse gases in the atmosphere increased during the 20th century as a result of human activities, mostly related to the use of fossil fuels (e.g. for electric power generation), agricultural activities and land-use change (mainly deforestation), and continue to increase. The increase has been particularly rapid since 1950. Compared with the pre-industrial era (before 1750), concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have increased by 34 %, 153 %, and 17 %, respectively. The present concentrations of CO2 (372 parts per million, ppm) and CH4 (1772 part per billion, ppb) have not been exceeded during the past 420 000 years (for CO2 probably not even during the past 20 million years); the present N2O concentration (317 ppb) has not been exceeded during at least the past 1 000 years.

The IPCC (2001) 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. These scenarios assume no implementation of specific climate-driven policy measures. Under these scenarios, greenhouse gas concentrations are estimated to increase to 650-1 350 ppm CO2-equivalent by 2100. It is very likely that fossil fuel burning will be the major cause of this increase in the 21st century.

The IPCC projections show that global atmospheric greenhouse gas concentrations are likely to exceed 550 ppm CO2-equivalent in the next few decades (before 2050). If this level is exceeded, there is little chance that global temperature rise will stay below the EU target of not more than 2 degrees C above pre-industrial levels. Substantial global emission reductions are therefore necessary to meet this target.

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.

Targets

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

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)

Constants

CO2

change in F = alpha ln (C/C0)

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

alpha = 5.35

CH4

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

where 

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

N2O

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

 

where 

 

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

HFC-23

0.16

CFC-11

0.25

HFC-134a

0.159

CFC-12

0.32

CF4

0.116

CFC-13

0.25

C2F6

0.26

CFC-113

0.3

SF6

0.52

CFC-114

0.31

CFC-115

0.18

 

 

HCFC-22

0.2

 

 

HCFC-141

0.14

 

 

HCFC-142

0.163

 

 

CCl

0.13

 

 

CH4CC

0.01

 

 

CH4CCl3

0.06

 

 

CH3Br

0.05

 

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.

Uncertainties

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.

Generic metadata

Topics:

Climate change Climate change (Primary topic)

Tags:
climate | csi
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 013
Geographic coverage:

Contacts and ownership

EEA Contact Info

Blaz Kurnik

Ownership

EEA Management Plan

2010 (note: EEA internal system)

Dates

Frequency of updates

Updates are scheduled once per year
Filed under: ,

Comments

European Environment Agency (EEA)
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Denmark
Phone: +45 3336 7100