The Carbon Dioxide Information Analysis Center (CDIAC)
- Current Greenhouse Gas Concentrations
T.J. Blasing and Sonja Jones
Updated February 2005
Gases typically measured in parts per million (ppm), parts per billion
(ppb) or parts per trillion (ppt) by volume are presented separately
to facilitate comparison of numbers. All pre-1750 A.D. concentrations,
Global Warming Potentials (GWPs), and atmospheric lifetimes are from
Table 4.1 of (Intergovernmental Panel on Climate Change) IPCC 2001
unless otherwise indicated. Additional material on greenhouse gases
can be found in CDIAC's Reference Tools. To find out how CFCs, HFCs,
HCFCs, and halons are named, see Name that compound: The numbers game
for CFCs, HFCs, HCFCs, and Halons.
Sources of the current atmospheric concentrations are given in the
footnotes. The concentrations given are frequently derived from data
available via the CDIAC web pages; many corresponding links are given
in the footnotes below. These data are contributed to CDIAC by various
investigators, and represent considerable effort on their part. We ask
as a basic professional courtesy that when you refer to any of these
data you acknowledge the sources. Guidelines for proper acknowledgment
are found at the end of the page for each link, except for the
ALE/GAGE/AGAGE database where acknowledgment guidelines are given in
the "readme" files; links to those "readme" files are given in
footnote 9, below.
GAS Pre-1750 concentration1 Current2 tropospheric concentration GWP
(100-yr time horizon)3 Atmospheric lifetime (years)4 Increased
radiative forcing5 (W/m2)
Concentrations in parts per million (ppm)
carbon dioxide (CO2) 2806,7,8 374.97 1 variable4 1.46
Concentrations in parts per billion (ppb)
methane (CH4) 7308/6888 18529/17309 23 124 0.48
nitrous oxide (N2O) 2708,12 319 9/3179 296 1144 0.15
tropospheric ozone (O3) 25 344 n.a.4 hours-days 0.354,5
Concentrations in parts per trillion (ppt)
CFC-11 (trichlorofluoromethane) (CCl3F) zero 2569/2539 4,600 45
0.34 for all halocarbons collectively, including many not listed here.
CFC-12 (dichlorodifluoromethane) (CCl2F2) zero 5469/5429 10,600 100
CFC-113 (trichlorotrifluoroethane) (C2Cl3F3) zero 809/809 6,000 85
carbon tetrachloride (CCl4) zero 949/929 1,800 35
methyl chloroform (CH3CCl3) zero 2810/2810 140 4.8
HCFC-22 (chlorodifluoromethane) (CHClF2) zero 15811 1700 11.9
HFC-23 (fluoroform) (CHF3) zero 1412 12,000 260
perfluoroethane (C2F6) zero 312 11,900 10,000
sulfur hexafluoride (SF6) zero 5.2111 22,200 3,200 0.0025
trifluoromethyl sulfur pentafluoride (SF5CF3) zero 0.1213 ~
18,000 ~ 3,200 (?) < 0.00015
1Following the convention of IPCC (2001), inferred global-scale
trace-gas concentrations from prior to 1750 are assumed to be
practically uninfluenced by human activities such as increasingly
specialized agriculture, land clearing, and combustion of fossil fuels.
2For most gases, concentrations for year 2003 are given, as indicated
more specifically in the footnotes below. Estimates for 1998, from
IPCC (2001), are given for CHF3, C2F6, and SF5CF3. The current (2002)
concentration of SF5CF 3 is probably around 0.16 parts per trillion
(see footnote 13). Atmospheric concentrations of some of these gases
are not constant throughout the year. Global annual arithmetic
averages are given.
3 The GWP provides a simple measure of the radiative effects of
emissions of various greenhouse gases, integrated over a specified
time horizon, relative to CO2 emissions. It is calculated using the
.... see website ....
where ai is the instantaneous radiative forcing due to a unit increase
in the concentration of trace gas, i, ci is concentration of the trace
gas, i, remaining at time, t, after its release and n is the number of
years over which the calculation is performed.
Formula taken from page 58 of IPCC 1990: Climate Change: The IPCC
Scientific Assessment. J.T. Houghton, G.J. Jenkins, and J.J. Ephraums
(eds.). Cambridge University Press, Cambridge, UK, 365 pp.
Unless otherwise indicated, GWP's taken from: IPCC 2001. Climate
Change 2001: The Scientific Basis. J.T. Houghton, L.G. Meira Filho,
B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell. Cambridge
University Press, Cambridge, UK, 944 pp. (see Technical Summary (TS)
of the Working Group 1 Report, page 47).
4The atmospheric lifetime is defined as: "the burden (Tg) divided by
the mean global sink (Tg/yr) for a gas in a steady state (i.e., with
unchanging burden)" (IPCC 2001, page 247). That is, if the atmospheric
burden of gas x is 100 Tg, and the mean global sink is currently 10
Tg/yr, the lifetime is 10 years. The atmospheric lifetime of carbon
dioxide is difficult to define because it is exchanged with reservoirs
having a wide range of turnover times; IPCC 2001, (page 38) gives a
range of 5-200 years. In contrast, most CH4 is removed from the
atmosphere by a single process, oxidation by the hydroxyl radical
(OH). The atmospheric lifetime of a gas is relatively easy to define
when essentially all of its removal from the atmosphere involves a
single process. However, some complications still arise. For example,
the effect of an increase in atmospheric concentration of CH4 is to
reduce the OH concentration, which, in turn, reduces destruction of
the additional methane, effectively lengthening its atmospheric
lifetime. An opposite sort of feedback applies to N2O: an increase
induces chemical reactions leading to an increase in ultraviolet
radiation available to photolyze the N2O, thereby shortening its
atmospheric lifetime (IPCC 2001, Section 4.1.4). Such feedbacks are
accounted for in the above table. The short atmospheric lifetime of
ozone (hours-days) precludes a globally homogeneous distribution;
ozone concentrations, and associated radiative effects, are greatest
near its sources. The "current" value given is an estimate of the
globally averaged value, from IPCC (2001), Table 4.1.
5Increased radiative forcing is the change in the rate at which
additional energy is made available to the earth-atmosphere system
over an "average" square meter of the earths surface due to increased
concentration of a "greenhouse" gas, or group of gases, since 1750.
Energy is measured in Joules; the rate at which it is made available
is in Joules/second, or Watts; hence, radiative forcing is measured in
Watts per square meter (W/m2). Numerical values for the radiative
fluxes are given in Table 6.11 on page 393 of IPCC (2001).; note
particularly the discussion of the uncertainty of the radiative
forcing for tropospheric ozone (cf. note 4, above). Radiative forcing
values for SF6 and SF5CF3 were calculated as the products of the
radiative efficiency values given in Table 6.7, and the concentrations
given in Table 4.1, of IPCC (2001). This calculation assumes that the
radiative efficiency has not changed with time, for these small
concentrations (cf. Mitchell 1989). For more details on SF5CF3, see
also W.T. Sturges et al. (2000).
6The value given by IPCC 2001, page 185, is 280 ± 10 ppm. This is
supported by measurements of CO2 in old, confined, and reasonably
well-dated air. Such air is found in bubbles trapped in annual layers
of ice in Antarctica, in sealed brass buttons on old uniforms,
airtight bottles of wine of known vintage, etc. Additional support
comes from well-dated carbon-isotope signatures, for example, in
annual tree rings. Estimates of "pre-industrial" CO2 can also be
obtained by first calculating the ratio of the recent atmospheric CO2
increases to recent fossil-fuel use, and using past records of
fossil-fuel use to extrapolate past atmospheric CO2 concentrations on
an annual basis. Estimates of "pre-industrial" CO2 concentrations
obtained in this way are higher than those obtained by more direct
measurements; this is believed to be because the effects of widespread
land clearing are not accounted for. The record derived from the "DSS"
Antarctic ice core, which covers the period from about 1000-1750,
indicates an average "natural background" concentration of 280.05 ppm.
7Current CO2 concentration (374.9 ppm) is the average of the 2003
annual values at Barrow, Alaska; Mauna Loa, Hawaii, American Samoa,
and the South Pole (one high-latitude and one low-latitude station
from each hemisphere). Refer to C.D. Keeling and T. P. Whorf for
records back to the late 1950s. Ice-core records provide records of
earlier concentrations. For concentrations back to about 1775, see A.
Neftel et al.; for concentrations back to about 1000 A.D., see D.M.
Etheridge et al.; and for over 400,000 years of ice-core record from
Vostok, see J.M. Barnola et al. All these data are available from CDIAC.
8Pre-industrial concentrations of CH4 are evident in the "1000-year"
ice-core records in CDIAC's Trends Online (See D.M. Etheridge et al.)
However, those values need to be multiplied by a scaling factor of
1.0119 to make them compatible with the AGAGE measurements of current
methane concentrations, which have already been adjusted to the Tohoku
University scale. Therefore, pre-industrial values calculated from the
ice-core data have been multiplied by 1.0119 before insertion in the
above table. Thousand-year records of CH4, CO2 and N2O, from ice-core
data, are also presented graphically in IPCC 2001, (page 6).
9The first value represents Mace Head, Ireland, a mid-latitude
Northern-Hemisphere site, and the second value represents Cape Grim,
Tasmania, a mid-latitude Southern-Hemisphere site. For CH4, these
values can be compared with the thousand-year ice-core records from
Greenland and Antarctica, respectively, discussed in the preceding
footnote. "Current" values given for these gases are annual arithmetic
averages based on monthly non-pollution concentrations for year 2003.
These data are compiled from data on finer time scales in the
ALE/GAGE/AGAGE database (R. Prinn et al.). These data represent the
work of several investigators at various institutions; guidelines on
citing the various parts of the AGAGE database are found in two README
within the ALE/GAGE/AGAGE database, also available via anonymous ftp.
10Recent data on methyl chloroform are the averages of monthly means
of in situ gas chromatograph data for 2003. These data are from the
National Oceanic and Atmospheric Administration (NOAA), Climate
Montitoring and Diagnostics Laboratory (CMDL), Boulder, CO. The first
value represents Point Barrow, Alaska, (71.3 N, 156.6 W, elevation:
8m) and the second value represents the South Pole station Antarctica
(89.98 S, 24.8 W, elevation: 2810 m). Atmospheric concentrations of
methyl chloroform have decreased appreciably in recent years. Recent
data are considered preliminary; for additional information about the
quality of the data, or any recent revisions, please contact the
principal investigators at one of the addresses given on the Web site
11Source: Climate Monitoring and Diagnostics Laboratory (CMDL) 2004.
Chapter 5. For SF6, see Figure 5.7. For HCFC-22, see Figure 5.8 and
Table 5.4. Data are global annual averages for year 2003.
Concentrations of SF6 through 1999, obtained from Antarctic firn air
samples, can be found in W.T. Sturges et al. See also W.T. Sturges et
12Source: IPCC (2001), Table 4.1; The pre-1750 value for N2O is
consistent with ice-core records shown graphically on page 6 of that
document. Estimates of "current" (1998) concentrations of CHF3and C2F6
are based on a variety of sources, including emissions rates and
annual growth rates. Data on CHF3 through 1995 can be found in D.E.
Oram et al.
13Taken from Table 4.1 of IPCC (2001); it is an estimate for year
1998. Assuming a ratio of SF6/SF5CF3 of 32; the current (2001)
concentration of SF5CF3 would be about 0.16 ppt. Concentrations of
SF5CF3 through 1999, obtained from Antarctic firn air samples, can be
found in W.T. Sturges et al. See also W.T. Sturges et al. (2000)
CMDL 2002. Climate Monitoring and Diagnostics Laboratory Summary
Report No. 26, 2000-2001, D.B. King and R.C. Schnell (eds.). U.S.
Department of Commerce, National Oceanic and Atmospheric
Administration, Climate Monitoring and Diagnostics Laboratory, Boulder
CO, 184 pp.
IPCC 1990. Climate Change: The IPCC Scientific Assessment. J.T.
Houghton, G.J. Jenkins, and J.J. Ephraums (eds.). Cambridge University
Press, Cambridge, UK 365 pp.
IPCC 1995. Climate Change 1994: Radiative Forcing of Climate Change,
and An Evaluation of the IPCC IS92 Emission Scenarios. J.T. Houghton,
L.G. Meira Filho, J. Bruce, Hoesung Lee, B.A. Callander, E. Haites, N.
Harris, and K. Maskell (eds.). Cambridge University Press, Cambridge,
UK 339 pp.
IPCC 1996. Climate Change 1995: The Science fo Climate Change. J.T.
Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg,
and K. Maskell (eds.). Cambridge University Press, Cambridge, UK 572 pp.
IPCC 2001. Climate Change 2001: The Scientific Basis. J.T. Houghton,
Y.Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K.
Maskell, and C.A. Johnson, (eds), Cambridge University Press,
Cambridge, UK, 881 pp.
Mitchell, J.F.B., 1989. The "greenhouse" effect and climate change.
Reviews of Geophysics 27(1), 115-139.
Sturges, W.T., T. J. Wallington, M.D. Hurley, K.P. Shine, K Sihra, A
Engel, D.E. Oram, S.A. Penkett, R. Mulvaney, and C.A.M.
Brenninkmeijer, 2000. A potent greenhouse gas identified in the
atmosphere: SF5CF3. Science 289, 611-613.
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