Just a bit of a theory coming.
If Swildons Hole
experiences high CO2 in hot weather especially down near sump one.
Usually ambient cave tempreture away from an exit or strong draught, stays fairly constant but in anyway only changes slightly and slowly.
Swildons is potentially very lucky (for airflow) as it now has two entrances
but virtuallyblocked by sump one.
Even if sump one were to be altered, there is a further problem, both entances are at the same altitude, so no chimney effect, so not usually much air flow, the pressure has to be differential.
In a house the chimney top has to be about 8 metres above the firemouth, to make it draw, hence bungalows seem to have outrageously tall chimneys.
So to get a strong throughflow of frsh air in the Swildons systen, not only would you have to remove sump one, keep mud sump open, you would also have to build a chimney on top of Priddy Green Sink.
Hope this helps.