I’d use a foaming glass cleaner and a cloth with a pole if needed.
It looks, though, like there’s not really a view to have to worry about so just a dusting might be enough and you could wipe any finger prints that are likely near the top with the glass cleaner. I think that’s one of those things no one’s gonna stress over.
This makes it really easy then, get an official looking sign made up, that reads “The Department of Interior has determined the backside of this glass to be a ‘microcosm preservation exihibit’. Please observe, but do not desturb. Thank you for your cooperation in preserving today for tomorrow. Our children will thank us.”
It’s always about tomorrows youth.