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."

Park officials are using a variety of media to cultivate those personal relationships. Golden Gate National Recreation Area uses podcasts to give park fans a chance to learn the science and follow impacts remotely. Yosemite's visitor center includes displays on climate change science and park impacts. In Glacier National Park, which has been at the forefront of the climate change response effort, rangers give a weekly “walk-and-talk” program on the past, present, and future of the park’s namesake features entitled “Where Have All the Glaciers Gone?”

According to Ardoin, these live, interpretive programs leave the biggest impression. Park interpreters and rangers, she said, have the skills and experience to be extremely effective climate change communicators. They spend their careers helping audiences develop intellectual and emotional connections to resources and the issues that affect them, and they are personally invested in those resources as well.

Rangers also have authority in the public's eye, particularly on controversial or politically charged subjects, Jarvis said. Whether it's ecosystem benefits of wildfire or race relations in a national historic site, "the park ranger doing the evening program doesn't embellish," Jarvis added. "The public expects us to deliver the unvarnished truth."

But to be effective, said Ardoin, Park Service rangers need to deliver a message on climate change that is as consistent as it is accurate. And progress so far has been sporadic.

Holly first gave a version of his presentation in 2007. He developed the original program on his own initiative, conducting his own research and using his own photos of Yosemite's iconic features. Since then, he has received support from the Park Service, including a four-day training course on climate change science and communication earlier this year. There, he met rangers from other National Parks, including the Florida Everglades, Oregon’s John Day Fossil Beds, and Alaska’s Kenai Fjords, who shared his enthusiasm for climate change education.

But Holly and his peers in the course – 20 rangers total – were the only applicants from the Park Service’s pool of more than 25,000 employees who found the motivation, time, and money to apply and attend. And despite the effort, Holly isn't sure when or whether he will be able to give his climate change presentation again. At 27, he only recently landed a year-round job with the Park Service. His official title is public information officer, meaning he usually spends his days answering phones and developing maps and brochures.

One of Holly's colleagues has offered a semi-regular program entitled "The Ups and Downs of Yosemite's Climate" in Tuolumne Meadows, on Yosemite's eastern border, throughout August. But in Yosemite Valley, there were no regularly scheduled ranger programs on climate change this summer. The valley is by far the more popular destination, attracting 70 percent of the park's visitors, while Tuolumne draws just over a third. In America's third most popular National Park, with an annual visitation of about four million, that's a big difference – and a lot of missed opportunities.

Still, the Park Service has a history of shaping public knowledge and behavior on natural resource issues.

Yosemite's staff, for instance, has worked hard to change public behaviors that attract bears to cars and campsites. After a record-breaking 1,500 bear incidents in 1998, the number of break-ins and other episodes fell by more than 80 percent in three years and has hovered between 100 and 200 incidents since 2005.

Climate change may be a problem of a different scale. But the underlying communication challenges are similar. If Yosemite rangers can sell bear canisters to a skeptical public, there's a chance they can work similar magic with fluorescent bulbs and hybrid cars.

Kate Johnson is a freelance author and graduate of Stanford University's environmental studies program. DailyClimate.org is a nonprofit news service that covers climate change.

On the web:

Yosemite National Park:

USGS report on Glacier National Park

USGS report on Joshua Tree National Park

UC Berkeley report on small mammals in Yosemite National Park

Golden Gate National Recreation Area climate podcasts

Yosemite National Park bear management information

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.