To use an API key, you first need to get one from the
Climate Data Service. You can do so, by creating an account
and then initialise the key at https://cds.climate.copernicus.eu/profile.
There are different locations where the key can be stored and where
cds_get_token() will look. It will look for the first successful value of (in order):
the environment variable named "CDSAPI_KEY", the R getOption() named "CDSAPI_KEY",
the environment variable named "ECMWF_DATASTORES_KEY", and the R getOption() named
"ECMWF_DATASTORES_KEY".
You can set the key at the start of each R session with cds_set_token(). If you
want a persistent solution, you can add the environment variable (with names shown above)
to your system. Or you can add the option (with the names shown above) to your
".profile" file. This will help you obscure your sensitive account information in your R script.