id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
158518147,MDU6SXNzdWUxNTg1MTgxNDc=,869,open netCDF gives 'time' dim with 1969 change in timezone,2049051,closed,0,,,5,2016-06-04T18:46:38Z,2016-06-04T20:20:46Z,2016-06-04T19:47:39Z,CONTRIBUTOR,,,,"I'm on xarray version 0.7.2
netCDF4-python version 1.2.2
Python version via Conda: 3.5.1 |Continuum Analytics, Inc.| (default, Dec  7 2015, 11:16:01)  [GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]

The `time` dim on Datasets read in from netCDF files seems to change timezones in 1969. This is especially a pain for annual data because the bug causes annual indexes to shift by one year. I've seen this problem in reanalysis for NCEP/NCAR, Twentieth Century Reanalysis, and some reconstructed SST fields.

For example, if a read in a netCDF file. Take NCEP/NCAR Reanalysis 1 monthly mean geopotential height as an example (ftp://ftp.cdc.noaa.gov/Datasets/ncep.reanalysis.derived/pressure/hgt.mon.mean.nc ; a 278 MB file).

``` python
import xarray as xr

ds = xr.open_dataset('~/Downloads/hgt.mon.mean.nc')
print(ds.time)
```

The interesting part of this printed time dim is always around 1969:

```
   ...
   '1969-09-01T00:00:00.000000000Z', '1969-10-01T00:00:00.000000000Z',
   '1969-11-01T00:00:00.000000000Z', '1969-12-01T00:00:00.000000000Z',
   '1969-12-31T17:00:00.000000000-0700',
   '1970-01-31T17:00:00.000000000-0700',
   '1970-02-28T17:00:00.000000000-0700',
    ...
```

You can see we go from `Z` to`-0700`. It also gives me an extra measure for Dec 1969 :-\

I don't think this is a hidden calendar or datetime-like feature that I'm unaware of...? Seems like a bug with you guys or upstream.

Thanks for your help!
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