It isn't hard for Denali National Park ecologist Carl Roland to see the ravages of climate change when he compares photos of Hidden Creek Glacier taken 88 years apart.
In the 1916 photograph, the Alaskan glacier wraps around a stony peak like an icy claw. But by 2004, the ice has released its grip and receded more than a mile.
Pictures of the Alaskan glacier offer a stunning visual contrast. Roland and other park researchers have been compiling many like them for the Denali Repeat Photography Project, a collection of old photographs of the park, matched with new pictures from the same viewpoint to show how the scene has changed.
More than 200 matched photos from across Denali––with interpretations and background information about the change––have been posted on the park's website.
The photo pairs provide visual evidence of recent changes in vegetation, water bodies, and glaciers. The magnitude of the changes suggests that a significant alteration of the park's ecosystems is likely being caused by a warming climate, Roland and his colleagues agree.
Often, the differences appear subtle and even benign to an untrained eye.
Near the upper reaches of the Savage River in the northeastern portion of the park, spruce trees have spread across once open river terraces in photos taken 29 years apart.
The landscape looks pristine, but the picture brings climate change into clear focus.
Roland often has to coach first-time viewers to take note of the increase in spruce trees in the more recent snapshot.
There are more trees because temperatures have warmed, creating longer and more nurturing growing seasons. That, in turn, means a changing habitat for animals: new varieties of vegetation appear; and in time, a treeless tundra turns into forest.
"If the predictions regarding future warming are realized," Roland said, the results are concerning, because they stand to be "unknown and potentially dramatic.
"We love our home now for all its attributes, but the scale and pace of change may make it seem a foreign country within a relatively short period of time."
Then and Now––and How
Temperatures across Alaska have increased by an average of 3.4° F over the last 50 years, and winter warming has been even greater, rising by an average of 6.3° F, according to data from the U.S. Environmental Protection Agency.
Higher temperatures mean increased risks of drought, wildfires, insect infestations, invasion of non-native plant and animal species, and the disappearance of native species.
The climate change storyline in Denali offers a cautionary tale for the global effects of ever-warming temperatures, said Dave Schirokauer, who leads a Denali park resources and science team that relies on Roland's work.
"We love those photos," he said. "They inspire us to figure out what is going on."
Denali's pristine landscape makes it easy to gauge climate change effects, Schirokauer said. And Roland's pictures tell the story better than tens of thousands of words, he added.
"When you see so clearly what's happening in the park you can then better understand how climate change will be affecting developed areas of the world," he said.
Schirokauer said higher temperatures will likely mean crops will shrink because less moisture will exacerbate droughts, coastal erosion will accelerate with sea-level rise and wildfires will increase.
The photography project began in 2005 when Fred Dean, an emeritus professor of wildlife biology at the University of Alaska, presented Roland with boxes full of 35mm slides and hundreds of prints, nearly 2,000 images in all.
"He asked if I was interested," Roland said. "I certainly was."
Dean had taken the photographs while flying over the park in a Piper Super Cub in 1975 and 1976 as part of an effort to produce a map of what was then Mt. McKinley National Park.
Along with the pictures were Dean's field notes, which included information precisely identifying the photos' locations. That meant Roland wouldn't have to traipse all over the park trying to find the same places.
Roland and other park staff members then made numerous trips on foot, by vehicle, or by helicopter to replicate, as closely as possible, the original photographs.
"That," he said, "was a challenge."
Roland did most of the photography from a helicopter, but it still wasn't easy.
"There were a hundred ways to be wrong and one way to be right," he said. "You could be too high, too low; a little left or a little right––all these ways that would skew the view."
In the end Roland found all the right angles and produced a study of the park's changing landscape that he said provokes "oh my gosh" reactions to the influence of climate change.
"When you can see it––it's much more dramatic," he said.
"It's not a bunch of technical jargon in some research paper. You can see it and understand it on an intimate level."