I was going to make a joke about how Austria is landlocked, how did we come up with the idea of making an ocean water standard.

Apparently the IAEA which is headquartered here set that standard, for anyone else curious.

you can of a lot of molecules though. and tgat is classically "physics" rather than "chemistry". Classical chemistry is reactiona between atoms or molecules to form new ones.

If you get deeper into it, the lines between chemistry and physics blur anyways.

The meter did not change, science has merely defined it more precisely and reliably over time. It is a measure of length, still one 40 millionth of the circumference of the earth through the poles. Other definitions like the speed of light definition will give you the same result. These newer definitions have reduced uncertainty and added ways to reproduce its length by natural means. But it's not like the 'original' meter was shorter or longer than today's meter, at least not by any noticeable margin.

Shifting the top end of a temperature scale by over five percent of the scale is a bit more arbitrary than that.