At first I thought that 増加 can be quantified while 上昇 cannot, but then I saw examples where 上昇 can be used to measure things like temperature and sea levels, which are also quantifiable. Is there a trick to knowing which word is used in what situations?
It seems that the difference is whether you want to express the increase of countable items, like number of people (where 増加 is used) or of a increase of a ratio/percentage (where 上昇 is used) but they did concede that even if you misuse it, it’s not too unnatural.