If litter is thrown on Mt. Everest and no one ever sees it, is it still an externality?

Reuters reports that a team of Nepali climbers will attempt to collect garbage in Mount Everest’s “death zone” (the area above 26,246 feet) for the first time this week.  Exhausted climbers have been leaving garbage in the death zone since the 1950’s, but Namgyal Sherpa, the expedition’s leader, says that global warming has revealed the extent of the problem: “The garbage was buried under snow in the past. But now it has come out on the surface because of the melting of snow due to global warming.”  The team also hopes to retrieve the corpse of a climber who died two years ago.

via freakonomics.blogs.nytimes.com