YOSEMITE NATIONAL PARK, Calif. - 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."
After the presentation, a few visitors approached Holly with general questions about Yosemite's trails and wildlife. An older couple, longtime volunteers in the Park, thanked him for inserting a new topic into the nightly rotation.
Talks like Holly's, while rare today, represent the future for the National Park Service, said agency director Jonathan Jarvis.
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.
"We host 280 million visitors a year," he said. "The public come to the national parks not necessarily with an intent to learn something. But it is our intent that they learn something."
In national parks across the country, the impacts of climate change are sobering. Scientists with the U.S. Geological Survey report that global warming could eliminate most glaciers from Glacier National Park within 20 years. Warmer temperatures and increased fire frequency over the next century could eliminate the Joshua tree from 90 percent of its current range within Joshua Tree National Park, according to another USGS study. In Yosemite, scientists from the University of California, Berkeley have documented many species, particularly small heat-sensitive mammals such as the American pika, moving to higher ground.
Those changes - some of which are readily apparent to park visitors – make communication easier, Jarvis said. "We're seeing climate change on the ground now in parks," he said. "That's an opportunity to demonstrate to the public that climate change is happening, in their lifetime, in real time, on the ground in front of them."
The threat to these popular recreation sites also gives the public a reason to care. Stanford University education professor Nicole Ardoin says that national parks have a personal and cultural significance that could inspire visitors to act on problems like climate change. "Talking about a very direct threat to those places brings up something very emotional related to climate change," she said. "It's a great time to reach people, when they're emotionally raw and ready to do something."
Jarvis agrees. It's hard for the public to relate personally to climate change, he said. But people "do relate personally to the national parks."