Temperature change (as little as a few degrees) can cause expansion. That's the
only time I had it happen to me.

Approximately 4-6 degrees will raise a properly topped up carboy about 1 inch.
That is assuming you consider a topped up carboy to be appximately 3/4 to 1
inch below the rubber stopper. (meaning into the neck if I am not being clear
enough). Barometric pressure has a lot to do with degassing. I am not sure of
it's relation to volume.