[CF-metadata] Emissivity not found in the current standard name table

[Jonathan Gregory]

Dear Young-In

Yes, by analogy with surface_albedo, I think surface_emissivity would be fine.

> - surface_ir_emissivity (or surface_longwave_emissivity)
It should be longwave, for consistence with other names.

> - surface_microwave_emissivity,
I think microwave would be OK; it would need a definition. You could also have
plain surface_emissivity and provide a (perhaps scalar) coordinate variable of
radiation_wavelength with bounds to specify the range to which it applies
precisely.

Cheers

Jonathan