SEWARD — A finger of ice spilling out of the Chugach Mountains marks Alaska's rapidly warming climate — almost literally.

The approach to Exit Glacier, the most accessible of the 500 square miles of ancient ice covering Kenai Fjords National Park, is a timeline of retreat.

On the road to the glacier's toe, on the trail winding below the forest canopy and, ultimately, on the mostly bare rock at the end of the trail are signs marking 195 years of accelerating pullback. Beyond the last sign, which marks the 2010 edge, is a chasm of open space showing how Exit Glacier has continued its retreat up the valley.

The loss measured last summer, 252 feet, was the biggest in any single summer on record. Over the year ending Oct. 1, after fall measurements were taken, the retreat was 293 feet, according to the National Park Service.

For repeat visitors, the changes are stark, said Sharon Kim, chief of resources at Kenai Fjords.

"Most science that you're doing, you may be measuring inches, centimeters, millimeters," Kim said. "Here, people just have to visit it again in a year or two."

Exit Glacier, a finger of cracked, blue-white ice that drops out of 700-square-mile Harding Icefield, some of it outside the park, is relatively small, only 14 square miles. But its public stature is large.

It was visited by a U.S. president — Barack Obama, who spent part of his 2015 Alaska trip at the glacier's melting terminus.

It has starred on television and video, including an episode of NBC's "Running Wild with Bear Grylls" that focused on Obama's visit.

It has a family link to a pop star. The Exit name comes from the pioneering 1968 ski traverse across the Harding Icefield by an expedition party that included Alaska homesteader Yule Kilcher, the grandfather of singer Jewel Kilcher. The group used the glacier to exit the icefield, and the name stuck.

It has a connection to the world's most famous sled dog race. Decades ago, Seward teacher Dan Seavey was among the locals who honed his dog-sledding skills in the glacier's valley, sometimes driving dogs directly onto the ice. He later raced in the bare-bones inaugural Iditarod Trail Sled Dog Race (the historic Iditarod Trail started north of Seward); now his son and grandson are professional mushers and repeat Iditarod champions who dominate the event, which has become a sports extravaganza.

Other well-known and much-visited Alaska glaciers are shrinking noticeably.

Mendenhall in the Tongass National Forest, a Juneau landmark and magnet for tourists and local outdoors enthusiasts, is shedding ice. Columbia, a tour boat destination in Prince William Sound, is one of the world's best-studied glaciers; retreat has caused the terminus to split into two thinner branches. Eklutna Glacier, source of Anchorage's drinking water and one of several glaciers in relatively accessible Chugach State Park, is well-studied and losing mass. Portage Glacier, one of multitudes of glaciers in Chugach National Forest, remains a big tourist draw even though visitors now have to take a boat ride across Portage Lake to see its face. It used to be visible from the shore of the lake.

Exit Glacier, which the Park Service says got over 181,500 visitors last year, is not Alaska's only walk-up glacier, albeit with a walk that has been getting longer as the glacier shrivels. But it stands out for its location in an easily accessible national park, the in-your-face documentation of its retreat and its role as a real-time climate change laboratory. Land-terminating Alaska glaciers like Exit, though they make up only a tiny percentage of the world's ice, are significant contributors to global sea-level rise, and visitors to Kenai Fjords are able to see that process up close.

For Sofia Heinonen, visiting from Argentina's glaciated Patagonia region, Exit Glacier and the Park Service's management of it prove good lessons for her country. She was hiking with a family group on July 5 and taking mental notes. She works for the Conservation Land Trust and is helping the Argentine government — which is coping with some of the same climate issues that face Alaska — expand its own national park system.

"We came here for inspiration," she said. "It's striking to see the same process in the South and in the North."

Each spring and fall, park workers go to the glacier to get detailed measurements of its terminus position. While last year's retreat was the biggest one-year loss measured, Kim, the resources chief at the park, said the annual measurements only go back a decade; before then, measurements were made every few years.

One important trend detected: The glacier is now retreating in winter as well as in summer, a pattern that has been consistent since 2006, according to a park report that describes Exit's geologic history. Since 2011, average October-to-May daily temperatures at the glacier's low elevations have been above freezing about half the time, the report noted.

An unpleasant trend: Park workers monitoring the glacier's retreating edge from 2013 to 2016 retrieved bags of human feces, with contents in fairly fresh condition, said Deborah Kurtz, physical science program manager at Kenai Fjords. In the past, mountaineers and glacier travelers at higher elevations used a bag-and-dump system to discard their waste into deep crevasses, as was the typical practice elsewhere, she said. Now climbers are instructed to carry out their waste, but past years' deposits, after being churned through the moving and melting ice, are now turning up at the end of Exit, she said.

Aerial photography and historic photographic records are also used to track the glacier's changes. The U.S. Geological Survey and researchers from the University of Alaska and University of Washington have crunched altitude data to calculate changes in the past half century at Exit and elsewhere. Reconstructing the more distant past requires analysis of data from the region's geology and tree rings.

Exit's rapid changes have forced the Park Service to make frequent adjustments along the trail system.

A pavilion built in 1987 to give visitors a place to rest in the shade was originally situated to provide a good view of the glacier; now the view is of alders that hem the structure after springing up in ground uncovered by the glacier's retreat. Information signs posted in the pavilion explain why the once-sweeping view is now obstructed, along with other effects of climate warming.

On the mile-long Exit Glacier trail, which once ended in a loop, the Park Service has had to make two significant extensions, adding a 540-foot spur in 2006 and a 420-foot extension of that in 2010. There will be no more extensions, Kim said, because the toe of the glacier is now surrounded by steep and treacherous terrain.

"We just can't continue to extend the trail any longer without it being really unsafe," she said.

The park in previous years had built, moved and rebuilt bridges along the trail, but managers gave up that program as well, she said. It is unlikely that any kind of similar structure would be put in near the glacier's current terminus, she said: "If you build something that has a lot of infrastructure, at some point it's going to be out of date again."

What about accommodating visitors in the future? A new management plan for the park's front country — the Exit Glacier area — is in the works to address that.

"Clearly, we have a situation where the glacier is changing. What does the public expect us to do, within a reasonable parameter?" Kim said.

Many park visitors are worried that the glacier will retreat too far for them to see it easily, according to surveys done by researchers at the University of Utah. Already, there is some disappointment at the end of the Exit Glacier trail.

Renee Shippey of Dallas, who visited Kenai Fjords in June and had been there in 2006 as well, was sorry that her granddaughter was unable to get the same close-up view of blue ice that was available 11 years ago.

"I remember walking over here," Shippey said. "You could see the blue. That's what I kept telling her: 'You're going to see the blue. You're going to see the blue ice.'"

Asked where the glacier would likely be when she grows up, 8-year-old Addisyn pointed far up the mountain.

Exit Glacier is only a small part of Kenai Fjords' ice and ice-influenced ecosystem that covers about half the 1,047-square-mile park.

Some Kenai Fjords glaciers are losing even more ice. Pedersen Glacier lost an average of 65 feet a year from 1951 to 1986, but that rate jumped to 410 feet a year from 1994 to 2015, scientists report. A lake at the toe of the glacier that was tiny two decades ago is now substantial. A similar lake formation has occurred at retreating Bear Glacier, south of Exit. Bear Glacier is more than five times as big as Exit and is losing more than 10 times as much ice annually, according to USGS-led research.

Park visitors willing to make the arduous hike up to the base of Harding Icefield at about 3,500 feet in elevation can see evidence of melt at the mother of all Kenai Fjords glaciers.

Tom and Julie Schulz, visiting from Minnesota, contrasted the current bare-ground conditions at the trail's summit with their snowy memories from a trip to the same spot in the mid-1990s.

"I'm shocked it changed this much," said Julie, with her husband and two daughters at the trail summit. Back then, poking out of the icefield, "there were just itty, bitty, little bits" of rock, she said. Now, disappearance of the ice has exposed those bits as mountains, she said.

The icefield has retreated over past decades but, more important, it has thinned, Kurtz said.

The Park Service has a mass-balance monitoring program that takes measurements each spring and fall to compare the icefield's annual snow accumulations with annual melts. Past results found the most mass loss at the icefield's lowest elevations; a new report on mass balance is pending.

Long-term changes are evident far downstream of the ice, an area getting new attention from scientists.

At Aialik Bay, the finger of water fed by Kenai Fjords' Aialik Glacier and other glaciers, old fish bones have recorded the story of marine waters warming since the early Industrial Age.

Isotope analysis of bones found from archaeological sites and of modern cod bones points to a temperature increase in that part of the Gulf of Alaska of 3.6 to 5.4 degrees Fahrenheit, according to a study published recently in the Journal of Archaeological Sciences: Reports.

The bones are from two sites, one about 200 years old and another about 100 years old, left by ancestors of today's Kenai Peninsula-area Sugpiaq people. Scientists were fortunate to find the cod bones in mounds full of seashells. The shells' calcium counteracted the soil's acidity and the cod bones were perfectly preserved, down to the delicate rib bones, said Aron Crowell of the Smithsonian Institution, a co-author.

The study examined bones from nine individual fish, six from the archaeological sites and three from modern times. The oxygen molecules in the fish ear bones, or otoliths, carry a record of life history.

"They're phenomenal. They're like little thermometers in the fish," he said. "If you slice it, you can see growth rings, just like trees."

The presence of oxygen isotopes with the atomic weight of 18 rather than the more common 16 in the otoliths is a marker of cold, he said. The colder the temperature, the more that heavier isotopes are present. Isotope analysis for modern fish bones matched modern Gulf of Alaska temperature records, and the methodology will work for bones from past times prior to written temperature records, potentially as far back as 5,000 years ago, he said. There are plans to expand the study and analyze more old fish bones from a wider part of the Gulf of Alaska, he said.

Chemistry of the marine water is changing as well.

The Park Service has launched a research project to track acidification in Kenai Fjords' marine waters, along with other characteristics like salinity, temperature and turbidity.

Acidification, a threat to shell-bearing organisms and marine life that eat them, has been linked elsewhere to melting glaciers — in Prince William Sound, for example — as increased torrents of freshwater dilute the saltwater and the calcium in it, pushing pH levels lower and more acidic. That adds to the acidification as marine waters absorb more atmospheric carbon.

Back on land and on the Exit Glacier road, the Park Service and U.S. Department of Transportation last year completed a makeover to cope with floods that had regularly closed off traffic in past years. The project, which cost about $3 million, raised the road and inserted culverts below it to try to keep rushing water out of vehicles' paths.

While glacial melt is swelling the volume in the creek and is making the area more watery in general, it turns out that the modern melt is likely not responsible for the sudden inundations that have forced road closures in recent years, a new study finds.

Much longer-term geologic processes are at work, the study concludes.

The meandering, braided creek and river channels that run down from the end of the glacier to the Seward Highway — and along the corridor that holds the road — are typical of the unstable waterways left behind after a glacier retreats. The biggest problems are in the area just beyond Exit Glacier's maximum extent during the Little Ice Age, which ended in the early 1800s. The sedimentary loads in the creek and river structures have yet to settle, and thus the water channels change.

"What we call flooding of that road is really the channels moving," said Janet Curran, a USGS hydrologist and lead author of the study. "We perceive it as flooding because the road's there."

The more modern melt at Exit Glacier and nearby Paradise Glacier is adding to that condition, said co-author Mike Loso, a National Park Service glacier expert. That is an "inherent consequence of glacial retreat everywhere," he said.

"Almost every glacial river in Alaska is carrying more water than it did 50 or 100 years ago because of the shrinking of the glaciers," Loso said. But where the road is concerned, "It turns out to be of secondary importance at Exit Glacier."

It will take years and maybe decades for the channels to settle on a stable pattern, Curran said.

The good news for Kenai Fjords is that Exit Glacier has retreated so far back that the rocky terrain left behind is solid and stable ground for the existing visitor facilities along the trail, Curran said.

"You could think of it as a terrace elevation," she said.