Listening to the husband-and-wife directing team of Adam Ravetch and Sarah Robertson describe it, the new big-screen nature documentary “Arctic Tale” was a vision that evolved unpredictably over 15 years, beginning as a photographic chronicling of wildlife in the arctic circle, but ending as a first-hand account of how animals are adapting by the year to a world unraveled by global warming.

“We really started to see radical changes from season to season about five years ago,” Mr. Ravetch said, recalling how his recent visits to the arctic differed wildly from his initial trips to the once-frozen tundra. “It was particularly striking this year, when we went back to the arctic in April and the ice was not even formed. There was much more open water than we had ever seen before, and if that ice wasn’t hard enough for us [to stand on], imagine what it’s like for a polar bear.”

Having initially set out to observe two animals in their natural habitats from infancy to adulthood — a polar bear and a walrus, which the couple described as one of the most massive yet least-understood sea creatures — Mr. Ravetch and Ms. Robertson’s observations in these later years began to change the focus of their movie, which arrives in New York theaters Wednesday.

“The changes to the habitat added elements we really felt a responsibility to show,” Mr. Ravetch said. “We could have easily made a film about a wintry paradise, and showed you all the animals of the arctic, but we felt a responsibility to follow the animals in the here-and-now. Bears and walruses don’t read headlines, they don’t know about global climate change, and we wanted to show the ways that their world is literally changing beneath their feet.”

As audiences will see in “Arctic Tale,” the changing temperatures are altering the basic rules of life for every local species — from migration patterns to hunting skills, maternal cycles and geographic locations. Through the course of the story, narrated by Queen Latifah, audiences follow two young polar bears as their mother is abruptly confronted with the perfect storm of shorter winters, thinning ice, and seals — a primary food source — that no longer give birth in the snow caves the bears know how to detect.

Simultaneously, we follow a young walrus that is nursed and taught by a mother and an “auntie” during her first two years of life. The stories intersect as Mr. Ravetch and Ms. Robertson record a remarkable, desperate act by both species: abandoning the deteriorating ice shelf for the open sea. As the ice breaks up all around them, the walrus clan heads out into the ocean for a life-risking swim to a nearby island. Meanwhile, starving and smelling the walrus’s scent on the waves, the polar bears follow suit, paddling to the point of exhaustion in hopes of reaching the island, and taking the uncommon action of attacking a herd of walruses as they lounge on the rocks.

“Once we saw the bear go out to the island, it became something close to a stakeout for us,” Mr. Ravetch said. “We’d set up on the island at the crack of dawn and wait all day — for an entire season — for an animal to go over into that herd. The seventh year, when the male polar bear attacked, it was a remarkable event.”

More than once, prior to filming on this island, Mr. Ravetch and Ms. Robertson said they found themselves to be victims of the rapidly changing arctic climate as well. In one nearly disastrous episode, Mr. Ravetch suddenly found himself separated from his crew, floating away on an ice raft that had broken off, separating the filmmaker from his Inuit guides. Determined to preserve the footage he had shot, Mr. Ravetch dove into the water and swam almost a quarter-mile while holding two cameras above the surface.

In another episode, the directors found themselves in a broken boat, floating out helplessly amid the pack ice for 72 hours while they waited for rescue and a replacement vehicle. It was there, ironically, that they were able to capture footage of newborn walruses that were only a few hours old. Ms. Robertson called it “some of the most amazing footage” of the entire project.

Released by National Geographic films, the same company that bought the French-made “March of the Penguins” in 2002 and opened it across America to astounding box office success, “Arctic Tale” was in production long before “Penguins” made the notion of a nature documentary a bankable concept for major movie studios. After spending the last two years in the editing room, whittling down some 800 hours of footage, and returning to re-shoot some sequences in hopes of capturing “the width and breadth of the arctic summer, and make [the movie] more cinematic,” the couple said they are now ecstatic that the movie will reach a mainstream audience.

“We’ve always known that these animals are living dramatic lives in the harshest place on Earth,” Ms. Robertson said. “And what we captured here should never be on TV. This stuff should always be on the big screen, in living color.”

For his part, Mr. Ravetch acknowledges that the success of “March of the Penguins” paved the way for “Arctic Tale” to receive a big-screen debut, and it’s something he believes will become more common as audiences vote with their money.

“Once upon a time, there wasn’t a genre called science-fiction, then they made one successful film and now it’s a very standard genre,” he said. “We’re interested in these natural history films and environmental trends, and it’s the place we want to go. It’s great that audiences now have the chance to experience it this way, to immerse themselves in this world.”