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Indicator Specification
The rationale for this indicator has not been described
The indicator shows the observed trends in greenhouse gas concentration levels. Greenhouse gases differ in the way they affect the climate system. In order to sum the effects of the individual greenhouse gases and other forcing agents in the atmosphere, the so-called ‘greenhouse gas equivalent concentration’ has been defined. This is the concentration of CO2 that would cause the same amount of radiative forcing as a mixture of CO2 and other forcing agents (greenhouse gases and aerosols).
Atmospheric concentration in parts per million in CO2 equivalents (ppm CO2e)
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 level (UNFCCC, 2009) and the EU level (October 2008 Environment Council conclusions), this ‘dangerous anthropogenic interference’ has been recognised by formulating an ambition of keeping the long-term global average temperature rise below 2 °C, compared to pre-industrial levels. In December 2015, the Paris Agreement strengthened this by stating its objective as ‘holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels’ (UNFCC, 2015).
No targets have been specified
No related policy documents have been specified
The trend in this indicator is based on combining data for numerous gases that affect the radiation balance on earth:
The trends in global average concentration levels of atmospheric CO2 for the period from 1950 are based on data available from the NOAA observatory (NOAA, 2020). Trend data for CH4, N2O, the fluorinated gases and other compounds under the Montreal Protocol were derived from station data that are available in the AGAGE (2020) data set. The global figures were derived by averaging the data from different observatory stations across the world, equally distributed over the northern and southern hemisphere. Pre-observational data for CO2, CH4 and N2O are based on ice core data (Etheridge et al, 1998, 2002, Machida, et al, 1995). Pre-observational data for F-gases are the result of modeling (Meinshausen et al, 2017). Data for the non-protocol agents are taken from IPCC (2013) and Myhre et al (2017).
Radiative forcings are calculated using an approximate equation according to IPCC (2013), based on the observed atmospheric concentrations and using radiative efficiencies for CO2, CH4, and N2O, O3 (both stratospheric and tropospheric) and vapour based on IPCC (2013). IPCC (2013) and Myhre et al (2017) estimates were used for the radiative forcing of non-protocol related compounds.
The equations used to compute contributions by the individual gases are presented below:
Trace gas |
Parameterisation, radiative forcing (F), in Wm |
Constants(IPCC, 2013; Butler, 2009) |
---|---|---|
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, depending on molecule (see below), taken from WMO, 2002. |
A similar approach was applied for the Montreal Protocol gases (i.e. CFCs & HCFCs)
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 alpha values used for Kyoto and Montreal Protocol Gases (see also CDIAC, 2011a, 2011b)
Kyoto Protocol gases |
Montreal Protocol gases |
||
HFC-23 |
0.18 |
CFC-11 |
0.26 |
HFC-134a |
0.16 |
CFC-12 |
0.32 |
HFC-32 |
0.11 |
CFC-13 |
0.25 |
HFC-125 |
0.23 |
CFC-113 |
0.3 |
HFC-143a |
0.16 |
CFC-114 |
0.31 |
HFC152a |
0.1 |
CFC-115 |
0.2 |
HFC-227ea |
0.26 |
HCFC-22 |
0.21 |
HFC-136fa |
0.24 |
HCFC-124 |
0.2 |
HFC-245fa |
0.24 |
HCFC-141 |
0.16 |
HFC365mf |
0.22 |
HCFC-142 |
0.19 |
CF4 |
0.09 |
CCl4 |
0.17 |
C2F6 |
0.25 |
CH3Cl |
0.01 |
SF6 |
0.57 |
CHCl3 |
0.08 |
SF5CF3 |
0.59 |
CHCCl3 |
0.07 |
NF3 |
0.2 |
CH3Br |
0.004 |
PCF-318 |
0.32 |
H1211 |
0.29 |
PCF-218 |
0.28 |
H1301 |
0.3 |
|
|
H2402 |
0.31 |
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. We used a factor of 0.154 (-) for correcting forcing of Montreal Protocol gases, based on IPCC (2013) (= -0.05 W/m2 or 10 ppm in 2015).
To quantify the total concentration of all greenhouse gases, the direct and indirect effect of multiple aerosols (sulphate, black carbon, organic carbon, nitrate, and mineral dust), and the forcing of tropospheric ozone, stratospheric water vapour, changes in albedo (e.g. due to black carbon) were added. Data on forcing have been based on IPCC (2013), Klimont et al, (2013), Wang et al. (2016), Nazarenko et al., (2017) and Myhre et al, (2017).
For the aerosols, we used figures, based on the 2013 IPCC report and subsequent literature. First, the direct radiative forcing (RFari) from 1850 to 2010 has been defined for the individual aerosols and tropospheric ozone, using IPCC (2013, Figures 8.7 and 8.8, Figure TS7, Table 8.6). Then, updates from Wang et al. (2014), Wang et al. (2016), Nazarenko et al., (2017) and Myhre et al (2017) have been used for the period 1990 to 2015. Finally, recent numbers of emissions have been used to extrapolate the time series until 2018. See table below for historic forcing of some of the aerosols and ozone. The historical indirect forcing of aerosols through cloud interaction (RFaci) has been defined by using the total forcing as provided by the IPCC (2013, annex II) and the direct forcing. This is done for the period up to 2011. Due to the lack of more recent data, the indirect forcing has been kept constant after 2011. Note that the net effect of biomass burning was kept to zero, as it is balanced by a positive forcing due to black carbon and negative forcing from organic carbon (see also IPCC, 2013, Table 8.4).
The climate forcing due to stratospheric vapour, aircraft contrails and land use are taken from IPCC (2013, annex II). The numbers have been kept constant at their 2011 value for the period 2011-2018, due to lack of more recent data.
Calculated direct radiative forcing for multiple aerosols and tropospheric ozone for a number of past years (W/m2)
Gas (group) |
2018 |
2010 |
1990 |
1950 |
1900 |
1850 |
Sulphate |
-0.34 |
-0.35 |
-0.39 |
-0.16 |
-0.06 |
-0.02 |
Black carbon (including snow albedo) |
0.45 |
0.46 |
0.41 |
0.30 |
0.17 |
0.05 |
Organic carbon (including secondary organic carbon.) |
-0.12 |
-0.12 |
-0.10 |
-0.06 |
-0.04 |
-0.02 |
Nitrate |
-0.17 |
-0.16 |
-0.11 |
-0.03 |
-0.02 |
-0.02 |
Tropospheric ozone |
0.41 |
0.40 |
0.37 |
0.16 |
0.09 |
0.04 |
If measurement data from a particular station are missing for a certain year, the global trend is derived from data available from other stations.
No methodology references available.
Global average concentrations since approximately 1980, are determined by averaging measurements from several ground-station networks (SIO, NOAA/CMDL, ALE/GAGE/AGAGE), with each network consisting of several stations distributed across the globe.
Absolute accuracies of global average annual concentrations are around 1% for CO2, CH4, N2O and CFCs; for HFCs, PFCs, and SF6, absolute accuracies are between 10 % and 20 %. The largest uncertainties have been determined for the concentration of different aerosols such as sulphur, and black and organic carbon. The uncertainty in the trend of these aerosols could be 50-60 % (IPCC, 2013).
Radiative forcing is calculated using parameterisations that relate the measured concentrations of greenhouse gases to radiative forcing. The overall uncertainty in radiative forcing calculations is shown in the tables below (given in 10 % and 90 % confidence ranges).
Best estimate RF values from 1750 to 2011(and 10 % and 90 % confidence ranges) (source: IPCC, 2013)
Group |
Forcers |
Best estimate |
10 % |
90 % |
Kyoto Protocol |
CO2 |
1.82 |
1.62 |
2.02 |
|
CH4 |
0.49 |
0.44 |
0.54 |
|
N2O |
0.18 |
0.15 |
0.21 |
|
HFC, PFCs, SF6 |
0.03 |
0.03 |
0.04 |
Montreal Protocol |
Montreal F-gases |
0.28 |
0.14 |
0.44 |
Non-Protocol |
Tropospheric O3 |
0.4 |
0.2 |
0.6 |
|
Sulphate aerosols |
-0.39 |
-0.59 |
-0.19 |
|
Nitrate aerosols |
-0.13 |
-0.18 |
0.08 |
|
Black carbon |
0.42 |
0.02 |
0.82 |
|
Organic carbon |
-0.12 |
-0.32 |
0.08 |
|
Land use |
-0.15 |
-0.25 |
-0.05 |
|
Vapour |
0.07 |
0.04 |
0.10 |
|
Mineral dust |
-0.10 |
-0.30 |
0.10 |
|
Air contrails |
0.05 |
0.01 |
0,10 |
|
Indirect effect (cloud interaction) |
-0.55 |
-1.1 |
0.10 |
|
|
|
|
|
|
Total |
2.32 |
1.2 |
3.4 |
Uncertainty in relation to peak concentration values
The IPCC (2014, 2018) has modelled concentration levels of all greenhouse gases in the atmosphere, which are consistent with keeping the global average temperature increase below 1.5 and 2 °C, for various probability levels. The indicator assessment uses those peak concentrations and 2100 concentration values of greenhouse gases in the atmosphere that, according to the IPCC, give a likely (67 %) probability of staying below a 1.5 °C and a 2 °C temperature increase by the end of the century. This means that the concentration could peak somewhere between 2020 and 2100, and then become (strongly) reduced again (e.g. through zero emissions and even negative emissions though active CO2 removal). The IPCC also introduced the temperature overshoot feature, which means that temperature targets may become temporarily exceeded, followed by a decrease later in the century. Risking such a temperature overshoot would put an additional burden on strong and even negative emissions reductions and, hence, this has not been considered in the messaging of this indicator. These values and other probability values are presented below to indicate the uncertainty and variation in peak and 2100 concentration values.
Peak and 2100 concentration levels of total greenhouse gases in the atmosphere consistent with keeping the global average temperature increase below 1.5 °C and 2 °C, for various probability levels. The ranges are given in brackets, (all based on IPCC, 2014, 2018)
Probability of staying |
Temperature |
1.5 °C |
|
2.0 °C |
|
|
|
Peak |
Concentration |
Peak |
Concentration |
>67 % (likely) |
No |
465 (445-485) |
411 (390-430) |
505 (470-540) |
480 (460-500) |
|
Yes |
485 (465-505) |
405 (385-425) |
520 (505-540) |
465 (440-480) |
50 % (33 %-67 %) |
No |
485 (465-500) |
440 (430-445) |
540 (510-560) |
520 (500-535) |
|
Yes |
525 (520-540) |
425 (410-435) |
560 (540-575) |
505 (480-530) |
<33 % (unlikely) |
No |
500 (480-530) |
470 (445-480) |
580 (550-615) |
570 (540-600) |
|
Yes |
535 (510-550) |
450 (425-460) |
600 (560-630) |
540 (505-580) |
|
|
|
|
|
|
No uncertainty has been specified
Work specified here requires to be completed within 1 year from now.
Work specified here will require more than 1 year (from now) to be completed.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/atmospheric-greenhouse-gas-concentrations-7 or scan the QR code.
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