Just to calm everyone down, they aren't *Fully enclosed*. Fresh air will be able to flow in and out while moving.
And as i've stated many times, there are similar systems in hotter climates around the world that work just fine. If it's absolutely critical i'm sure you would be evacuated, but that would be an extreme case. It's not like we will ever be all that high off the ground (by gondola standards) anyway. These will be at about monorail height.