error in xarray-data.ipynb ?

[Carreau]

running the notebook, on the line

elevation = ds['elevation'].isel(ensemble=0).persist()

It seem like .isel(ensemble=0) is unnecessary as ds['elevation'] does not seem to have the ensemble dimension (and thus raise an error, at least for me and pangeo.pydata.org.

>>> ds['elevation']
<xarray.DataArray 'elevation' (lat: 224, lon: 464)>
dask.array<shape=(224, 464), dtype=float64, chunksize=(224, 464)>
Coordinates:
  * lat      (lat) float64 25.06 25.19 25.31 25.44 25.56 25.69 25.81 25.94 ...
  * lon      (lon) float64 -124.9 -124.8 -124.7 -124.6 -124.4 -124.3 -124.2 ...
Attributes:
    long_name:      Terrain Elevation
    standard_name:  elevation
    units:          meters