Standing on a rocky outcrop some 16,000 feet above sea level, mountain ecologist John All stares intensely at the glacier that leads up to the summit of Mount Maparaju, another 1,500 feet above us.
It should form a gentle convex arc from where we stand all the way up to the peak, perhaps half a mile away. For an experienced mountaineer like him, heading to the summit ought to be nothing more than a 90-minute stroll.
Instead, the glacier surface, ravaged by climate change, has sunk so dramatically that going straight up now would entail a technical climb up a 70 degree slab of ice.
All, who since 2011 has been conducting annual surveys of the effects of global warming here in Huascaran National Park, in the heart of the Peruvian Andes, estimates that the glacier surface has dropped around 170 feet just since he was last here 12 months ago.
In other words, the volume of ice lost just over the last year would be more than enough to fill an NFL Stadium.
“What is surprising is that the rate of melting is changing so quickly,” said All, a research professor at Western Washington University and head of the American Climber Science Program. “We always knew it was not going to be linear but now it feels exponential.”