Background information:
20th century GHG concentrations & natural forcings

Summary

A set of 20th century global and annual mean mixing ratios was compiled based on available authoratative sources. The greenhouse gas mixing ratios, in particular CO2, N2O, HFCs, PFCs, SF6 and the ozone depleting substances ODS, are recommended for being used in the 20th century runs in preparation of IPCC AR5. Here, data is provided for the full time span from 1765 to 2005, although modelling groups might decide to start their model runs only in 1850. Please consult the CMIP5 PCMDI website for further information in regard to other compounds, including short-lived greenhouse gas concentration fields for tropospheric ozone or methane. These additional short-lived compounds are included in the above consolidated datasets in some cases but are not the CMIP5 recommendation.

Please find below an overview of the data sources used to create the consolidated 20th century mixing ratio dataseries provided on this website:

Historical CO2 concentrations

End-of-year CO2 - concentrations (ppm): up to 1832: Law Dome Ice Core data (Etheridge et al.) 75yr smoothed data as provided on ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/law/law_co2.txt,
1982 to 2008:NOAA global-mean - as provided on: ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_annmean_gl.txt
1959 to 1981: Keeling MLO record with 0.59 ppm subtracted. 0.59 ppm is the mean MLO minus NOAAglobe value over 1982-1986.
Note that there are NOAAglobe data for 1980 and 1981, but these are not used because they are less consistent with MLO than for subsequent years.
The 1982 NOAAglobe and adjusted MLO values are the same at 340.56 ppm.
For 1823 through 1958 the Law Dome 20-year smoothed data are used. No correction is required because the mean difference, Law minus adjusted MLO over 1959-1963 is virtually zero (-0.006 ppm).
All data is derived from annual means, but averaged so that end-of-year concentrations are derived.
Compiled by: Tom Wigley and (a little bit by) Malte Meinshausen
Date: 10-Oct-2008 21:09:25 & updated 22-Sept-2009 18:46:24

Historical CH4 concentrations

Observed global end-of-year CH4 concentrations (ppb)
up to 1850, Law Dome Ice Core data (Etheridge et al.) data as presented on ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/law/law_ch4.txt ; from 1850 and later as for NASA GISS model as presented on http://data.giss.nasa.gov/modelforce/ghgases/Fig1B.ext.txt ;
1850-1980: Etheridge, D., L. Steele, R. Francey, and R. Langenfelds 1998.
Atmospheric methane between 1000 A.D. and present: Evidence of anthropogenic emissions and climate variability. J. Geophys. Res. 103, 15979-15993.
1984-2003: E. Dlugokencky (NOAA CMDL, private communication).
2004-2008: NOAA/ESRL/Global Monitoring Division flask data ftp://ftp.cmdl.noaa.gov/ccg/ch4/flask/month/
Date: 22-Sep-2009 19:24:34

Historical N2O concentrations

Nitrous Oxide (N2O) end-of-year average mixing ratio (ppb)
up to 1850 data from Flückiger et al. - (300yr cutoff spline);
from 1850 onwards: data from NASA GISS GCM - as given on http://data.giss.nasa.gov/modelforce/ghgases//Fig1C.ext.txt
1850-1977: Machida, T., T. Nakazawa, Y. Fujii, S. Aoki, and O. Watanabe 1995. Increase in the atmospheric nitrous oxide concentration during the last 250 years. Geophys. Res. Lett.,22, 2921-2924.
1978-1999: NOAA CMDL Flask Data ftp://ftp.cmdl.noaa.gov/hats/n2o/flasks
2000-2008: G.S. Dutton, T.M. Thompson, J.W. Elkins and B.D. Hall (NOAA CMDL InSitu Data) ftp://ftp.cmdl.noaa.gov/hats/n2o/insituGCs/CATS/global/insitu_global_N2O
Date: 22 Sep-2009 19:45:35

Historical C2F6 mixing ratios

Data: Global average mixing ratio
Unit: Parts per trillion (ppt)
Description: End of year historical C2F6 mixing ratio determined from firn air (Worton et al. 1997, Fig 2b - model results 1940 to 2001; linearly interpolated to zero levels in 1900)
Source: Worton et al. 2007, Figure 2b, http://pubs.acs.org/doi/pdf/10.1021/es061710t
Date: 18-Jul-2006 10:44:17

Historical CF4 mixing ratios

Data: Global average mixing ratio
Unit: Parts per trillion (ppt)
Description: End-of-year Historical CF4 mixing ratio determined from firn air 1940 to 2003 (Worton et al. 1997, Fig 2a - model results; assuming constant gdecline rate to zero pre-industrial values of 34ppt in 1900)
Source: Worton et al. 2007, Figure 2a, http://pubs.acs.org/doi/pdf/10.1021/es061710t , except the initial years 1900-1922 are kept constant at assumed pre-industrial value of 35ppt, given Worton et al. 2007 estimate of 34ppt and Deeds, D. A., J. Mühle, and R. F. Weiss (2008), Tetrafluoromethane in the deep North Pacific Ocean, Geophys. Res. Lett., 35, L14606, doi:14610.11029/12008GL034355, http://www.agu.org/pubs/crossref/2008/2008GL034355.shtml
Date: 18-Jul-2006 10:44:17

Historical HFC125 mixing ratios

Data: Global average mixing ratio
Unit: Parts per trillion (ppt)
Description: Input with historical mixing ratio data, based on Oram et al. (1998) and figure 1-23 WMO 2006, linearly interpolated to zero between 1980 and 1970
Source: WMO 2007, Fig 1-23
Compiled by: G. Velders, S. Smith, M. Meinshausen Date: 03-Aug-2009 17:23:01

Historical HFC134a mixing ratios

Data: Global average mixing ratio
Unit: Parts per trillion (ppt)
Description: Input with historic end-of-year data - note that the Montzka et al. NOAA/ESRL/GMD data only extended to July 2008. All given concentrations are end-of-year values, assumed equal with the following years start-of-year values.
Source: (NOAA/ESRL/GMD), available here ftp://ftp.cmdl.noaa.gov/hats/hfcs/134A_MS2008a.txt ; Montzka et al. (1996), Observations of HFC-134a in the remote troposphere, GRL, 23, 169-172, 1996. and Montzka et al. (1996) Decline in the tropospheric abundance of halogen from halocarbons: Implications for stratospheric ozone depletion. Sent by Steve Montzka in email on Thu, 07 May 2009 13:48:33 -0600
Compiled by: Steve Montzka, Steve Smith, Malte Meinshausen
Date: 03-Aug-2009 09:37:46

Historical HFC143a mixing ratios

Input with historical data taken from Culbertson et al., Table 1 (interpolated end-of-year values between 1978 and 1996); linear interpolation to assumed zero level in 1970 and linear extrapolation to year 2000 Source: Culbertson, et al., Chemosphere 55, 1109-1119, 2004 Date: 12-Aug-2009 00:14:09

Historical HFC23 mixing ratios

Oram et al. (1998) with extension until 2004 as provided in WMO 2006 Fig 1-23 and extension back to 1930 assumed linearly.

Historical SF6 mixing ratios

Input with historical end-of-year mixing ratio data, from Montzka et al. (pers. communication) beginning of year 1961 - 2008, set equal to end-of-year 1960-2007, linearly interpolated to zero between 1950 and 1960 Source: SF6 is regularly measured at multiple NOAA sites and by different techniques. A record from firn air, flasks, and in situ instruments is compiled from Butler et al., 1999, Geller et al., 1997, and from G. Dutton (S. Montzka, personal communication) Date: 03-Aug-2009 15:47:39

Solar forcing

Solar irradiance by Lean et al. as recommended for CMIP5, as documented here: http://www.geo.fu-berlin.de/en/met/ag/strat/forschung/SOLARIS/Input_data/CMIP5_solar_irradiance.html - converted into radiative forcing by dividing by 4 (geometrical) and multiplying by 0.7 (albedo) effect. Furthermore, the data is normalized to have an average zero around 1750 (22 years around 1750).

Volcanic Stratospheric Aerosols

Note: This is not a CMIP5 recommendation. Please consult PCMDI CMIP5 website for more information. Monthly Volcanic radiative forcing - relative / unscaled - as in NASA GISS model, using a optical thickness to radiative forcing conversion of -23.5 Source: NASA-GISS: http://data.giss.nasa.gov/ , manually extended by zero forcing from 2001 to 2006 Date: 15-Jun-2006 00:20:54

Contact

Malte Meinshausen (malte.meinshausen +add+ pik-potsdam.de)
Steve Smith (steve.smith +add+ pnl.gov)
RCP3-PD (IMAGE): Detlef van Vuuren (detlef.vanvuuren +add+ pbl.nl)
RCP4.5 (MiniCAM): Allison Thomson (Allison.Thomson +add+ pnl.gov)
RCP6 (AIM): Toshihiko Masui (masui +add+ nies.go.jp)
RCP8.5 (MESSAGE): Keywan Riahi (riahi +add+ iiasa.ac.at)