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  • Pat Neuman
    Current Greenhouse Gas Concentrations http://cdiac.ornl.gov/pns/current_ghg.html T.J. Blasing and Sonja Jones Updated February 2005 Gases typically measured in
    Message 1 of 1 , Feb 13, 2005
      Current Greenhouse Gas Concentrations
      http://cdiac.ornl.gov/pns/current_ghg.html
      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
      formula:

      .... 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
      files (http://cdiac.ornl.gov/ftp/ale_gage_Agage/AGAGE/gc-md/readme.agA
      and http://cdiac.ornl.gov/ftp/ale_gage_Agage/AGAGE/gc-ms/readme.agA)
      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
      ftp://ftp.cmdl.noaa.gov/hats/.

      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
      al. (2000).

      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)

      REFERENCES

      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.


      ----------------

      CDIAC is located within the Environmental Sciences Division (Gary K.
      Jacobs, Director) at Oak Ridge National Laboratory in Oak Ridge,
      Tennessee. CDIAC is co-located with Environmental Sciences Division
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      carbon cycle and the effects of carbon dioxide on vegetation. And
      CDIAC staff are connected with current Oak Ridge National Laboratory
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      --------------------------

      Carbon Dioxide Information Analysis Center

      http://cdiac.ornl.gov/about/intro.html

      The Carbon Dioxide Information Analysis Center (Thomas A. Boden,
      Director), which includes the World Data Center for Atmospheric Trace
      Gases, is the primary global-change data and information analysis
      center of the U.S. Department of Energy (DOE).

      CDIAC responds to data and information requests from users from all
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      in the biogeochemical cycles of greenhouse gases; emissions of carbon
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      elevated carbon dioxide on vegetation; and the vulnerability of
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      On the other hand, CDIAC does not specialize in information on the
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      CDIAC is supported by DOE's Climate Change Research Division of the
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      in the multi-agency Global Change Data and Information System. Wanda
      Ferrell is DOE's Program Manager with responsibility for CDIAC.

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