Does CMIP7-prep calculate global sums?

In the CMIP7 data request, there are fields that represent a total (i.e., integrated) quantity. One example is `atmos.co2mass.tavg-u-hm-u.mon.glb` which is documented as "Total atmospheric mass of Carbon Dioxide" in kg.
What value or formula should be presented so that CMIP7-prep computes the correct globally-integrated quantity?

Start by tracing how CMIP7-prep handles the `atmos.co2mass.tavg-u-hm-u.mon.glb` variable and compare that path with its CMIP7 data-request definition. Confirm the appropriate globally integrated value or formula with the project discussion, then verify that the computed result matches the documented total atmospheric carbon-dioxide mass.

Written by the indexing model from the issue text.