Once upon a time, the easiest way for a visitor to touch ice  in Peru was to climb the tourist trail to Pastoruri Glacier, a flat-topped glacier 70 km south of Huaraz. Roads from the highway made the glacier easily accessible to daytrippers, and even though its peak is a staggering 5,200 meters above sea level, the trek upward is relatively gentle, as far as glaciers go. If things got really rough, you could always rent a burro or a horse in the parking lot and haul yourself up that way. Not now. No longer. There are no burros for hire at Pastoruri because the glacier is officially off-limits to…