On any given summer evening about 60 tourists gather in campground amphitheatres here for park ranger presentations. Astronomy, geology, human history, fire ecology are on the regular schedule of program topics. Wilderness safety and Yosemite's notoriously aggressive black bears are also popular.
But one July evening Yosemite ranger Matt Holly popped something different onto his projector screen: "Yosemite's climate: Past...and Future?"
What followed was a rare and relatively new occurrence in Yosemite Valley - a ranger program focused exclusively on how one of the jewels of America's national parks system is responding to a changing climate.
During the hour-long slide show, Holly summarized the effects of climate change in Yosemite - including shrinking waterfalls, intensifying wildfires, and vanishing species.
He didn't flinch from controversy, presenting evidence for human influence on global temperature and debunking common "natural causes" myths.
"In pretty much every scientific organization, every government - you're going to be hard pressed to find someone who says climate change isn't happening," Holly told his audience. "There really isn't a whole lot of debate about it."
Two years ago Jarvis launched a system-wide Climate Change Response Program. Communication, research, adaptation, and mitigation are the four main components. The Park Service has a legion of scientists, biologists, geologists and other experts working on the latter three.
But communication and education, Jarvis said, may ultimately prove to be the agency's biggest contributions to the field.