Air temperature could possibly do it or at least contribute, as was the case with SARS in 2003.

It's 35C in Bangkok, 36C across Malaysia and 32C in Singapore.

How much hotter do you think it would have to get to make that virus die out?

Most Singapore buildings and its public transport system are fully A/C.

It's similar for Malaysia and Thailand since they're still in the tropics, except those countries are less dense.

There's plenty of AC in the US as well.

As far as I can tell the virus isn’t spreading like crazy in Bangkok, Malaysia, or Singapore. Singapore had it way worse in 2003, still the SARS virus withered came June.

wouldn't that be only a local effect though, e.g. Southern vs Northern Hemispheres?

The Northern Hemisphere account for ~90% of the world's population; the percentage living beyond 23.5°S is very small. It is entirely conceivable that the epidemic is put under control before it gets too cold for those people.