how to get absolute local temperatures?

[mathause]

This is just a small note how we can potentially get to absolute temperatures from the temperature anomalies we use in mesmer.

# gridded annual observed temperatures
obs = ...
# gridded annual model temperatures 
tas = ...

REFERENCE_PERIOD = slice("1850", "1900")
OBS_PERIOD = slice("1991", "2020")

offset = (
    # re-base model to modern temperatures
    tas.sel(time=REFERENCE_PERIOD).mean("time")
    - tas.sel(time=OBS_PERIOD).mean("time")
    # add the observed absolute temperatures
    + obs.sel(time=OBS_PERIOD).mean("time")
)

Thanks @yquilcaille