Introduce `units_metadata` attribute to clarify the meaning of quantities involving temperature

[JonathanGregory]

This issue arises from issue 101 of the discuss repo, opened by @larsbarring, about the need to clarify the meaning of quantities whose units involve temperature. After lengthy discussion, a working group was convened (@davidhassell @larsbarring @taylor13 @sebvi @semmerson @sethmcg @ethanrd @JonathanGregory) to develop a detailed proposal. It was agreed in discuss issue 101 that the proposal of the working group should be treated by the community as one which has already been agreed in principle. That proposal is set out in discuss issue 101 for review. Any comments should be concerned with clarity, style, and so on, not with content.

The purpose of the present issue is solely to implement the proposal, through pull request 480.

[edavis]

Hi @JonathanGregory — Just a heads up, you're pinging the wrong E. Davis :)

I think you're looking for @ethanrd, instead.

[JonathanGregory]

Quite right - thanks for correcting me, @edavis

[JonathanGregory]

To aid review, I've made rendered versions of the conventions document (pdf html) and conformance document (pdf html).

[JonathanGregory]

If you have any suggestions for ways to improve the clarity and detail of the proposal, or if you see any conceptual difficulty that invalidates it, please comment on https://github.com/cf-convention/vocabularies/issues/125 (which is where all previous discussion has taken place i.e. not here in #481) before Tuesday 28th November, when it will otherwise be accepted. Thanks.

[davidhassell]

Hello - as things stand PR #480 will get merged on Monday 4th December 2023, so if you haven't reviewed it yet but would like to, time is running out ....

Thanks, David