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 :


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 :

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 :


where basedir (ending with IGCM) is defined for the various computing centers in

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.

Last modified 11 months ago Last modified on 02/28/20 10:54:30