@Dave-Allured : I think this does deserve some further discussion because the
study of climate in the distant past is a very important part of climate
science, even if it is small in scale compared to the study of present day
climate. Our problem is that the distant part is more important for our
community than it is for many of the people who work on standards for dates and
times.
The NetCDF4 library may have resolved this for us, unless we make an active
decision to depart from the treatment of negative reference times in NetCDF4.
For example, if I create a file from the following CDL using `ncgen` (from
version 4.6 of the NetCDF library):
```
netcdf time_ex01 {
dimensions:
time = 3 ;
variables:
double time(time) ;
time:standard_name = "time" ;
time:units = "days since -0001-01-01" ;
time:calendar = "standard" ;
// global attributes:
:Conventions = "CF-1.7" ;
data:
time = 0, 365, 731 ;
}
```
and then run `ncdump -t`, the resulting time values are given as: `time =
"-0001-01-01", "0000-01-01", "0001-01-01" ;`. i.e. NetCDF4 interprets
`0001-01-01` as being two years after `-0001-01-01`. Unfortunately, this is not
well documented in the NetCDF User Guide, but it is unambiguous. I think this
takes precedence over the `cftime` library, because we are trying to build on
top of the NetCDF data model ... but there may be other interpretations of that.
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