Single-precision output namelist option does NOT work (rtmhist_ndens)

[ekluzek]

The single-precision output namelist option is NOT functional. Output is always double precision even when rtmhist_ndens==2. This problem goes back a long way because it looks like the option was never implemented.

[ekluzek]

A fix for this came in with release-cesm2.0.01. It converts to single-precision when history output is being written.

[ekluzek]

Reopening this issue as the fix isn't extensive enough. We've seen cases where numeric conversion issues kill simulations when there is some problem with the data values (when history is written). Also since you only detect the issue when history is written rather than by internal conversion to the history buffers, you don't detect issues right away. Thus we plan to fix this with single-precision history buffers, similarly on how it's done in CTSM.