Change atmospheric CO2 scalar value

Author: J. Ghattas
Last revision: 2020/28/02, A. Ducharne

For both offline and coupled simulations, the scalar value for atmospheric CO2 can be set in PARAM/run.def using ATM_CO2=x, with a default of 350 (ppm).

If you want to change for a constant value, set it directly in run.def, for example:

ATM_CO2 =  700.

For an annual change in CO2, using libIGCM, you can add an ascii file with annual values and the driver will update ATM_CO2. The file has to be written with the following syntax :

Annee_1990=352.00
Annee_1991=353.55
Annee_1992=355.09
Annee_1993=356.63
Annee_1994=358.16

The file must be added to the input files and it must be called CO2.txt. To do so, add a line like below in section BoundaryFiles/ListNonDel, either in stomate.card for offline runs, or in lmdz.card for LMDZOR :

[BoundaryFiles]
ListNonDel= (../../../yourfile_CO2.txt, CO2.txt)

You must also keep the default setting of ATM_CO2 in PARAM/run.def (do not comment it out):

ATM_CO2 =  _AUTO_: DEFAULT = 350.

Files with CO2 values according to the CMIP6 and TRENDY2 protocol can be found at the shared repository. For exemple :

basedir/ATM/GHG/CMIP6/ssp/ssp585/CO2_CMIP6_2015_2500.txt
basedir/ATM/GHG/CMIP6/historical/CO2_CMIP6_0000_2014.txt
basedir/SRF/CO2/CO2_1860_2012_TRENDY2.txt

where basedir (ending with IGCM) is defined for the various computing centers in ​https://forge.ipsl.jussieu.fr/igcmg_doc/wiki/Doc/ComputingCenters/SharedFiles

NB! Note that if the year you simulate (with varying CO2) is not in the file, run.def will contain an empty variable "ATM_CO2=" and the model will of course crash.