The world’s tragedies often have images that end up defining them: A five-year old screaming in Iraq after her parents were killed by U.S. soldiers. A starving child being stalked by a vulture during a ruthless famine in Sudan. 
 
 A video released this week of an extremely emaciated polar bear has served as a similar purpose: as a rallying cry and stand-in for a largely unmitigated environmental disaster. 
 
 The video was shot by Paul Nicklen, a nature photographer and contributor to the National Geographic magazine for the last 17 years. He is also a biologist by training and the co-founder of Sea Legacy, a nonprofit that uses storytelling and images to advocate for the environment. 
 
 Nicklen’s video, which he shot on a trip for Sea Legacy, depicts an emaciated polar bear, its coat patchy, seemingly near death on an island in a Canadian territory inside the Arctic Circle. It searches for food in a rusted garbage can and chews what Nicklen said was an old snowmobile seat. 
 
 And it struck a nerve. It was viewed more than 3.5 million times in posts on Nicklen’s and National Geographic’s Instagram feeds, according to metrics on the photo sharing site, before picking up news coverage from around the world. 
 
 If you have any conscience at all, this video of a starving polar bear will break your heart. We cannot look away. https://t.co/6xPkl45FLp — Maryn McKenna (@marynmck) December 9, 2017 
 
 In his caption with the video, Nicklen wrote that his team’s members were “pushing through their tears” while documenting the bear. 
 
 “It’s a soul-crushing scene that still haunts me, but I know we need to share both the beautiful and the heartbreaking if we are going to break down the walls of apathy,” he wrote. “This is what starvation looks like. The muscles atrophy. No energy. It’s a slow, painful death.” 
 
 [Without action on climate change, say goodbye to polar bears] 
 
 The photo was shot on Somerset Island in the upper reaches of Canada. Nicklen and his team saw the bear and shot the video from about 400 feet away, he said. Nicklen, 49, who grew up in the region on nearby Baffin Island, said that he had never seen a bear in such poor condition before. 
 
 “We stood there crying — filming with tears rolling down our cheeks,” he told National Geographic. 
 
 He said that the intent behind the footage, which is set over a mournful soundtrack, was not purely journalistic. The trip he was on was part of a push to drive home the issue of climate change with Sea Legacy. Though he said that he had no definitive proof that the bear’s condition was connected to the global phenomenon, he said he wanted to show people what a starving bear looked like and let them draw their own conclusions. 
 
 “We are a visual species,” Nicklen said in a phone interview. “He should have been a dominant bear. Why he was dying, I don’t know.” 
 
 A shot of another emaciated polar bear taken by a photographer in 2015 raised similar questions. 
 
 Polar bears face an existential threat from climate change due to the loss of habitat from melting sea ice, scientists believe. The populations of some 25,000 polar bears in 19 locations worldwide are forecast to decline by as much as a third in the coming decades. As their hunting and breeding grounds shrink, polar bears face an increased threat of starvation. 
 
 More than any other animal, polar bears have become the poster animal for climate change. Former vice president Al Gore used a cartoon of an exhausted, endlessly swimming polar bear to illustrate the impact humans were having on the sea ice where the bears once hunted. And studies and government agencies continue to warn that climate change could make polar bears extinct by 2050. 
 
 A paper published in July said that the higher global temperatures go, the more likely polar bears are to interact with humans — and possibly attack and eat them. 
 
 Some expressed skepticism that anything could be gleaned about the environment from one image. A commenter on the National Geographic’s Facebook page wondered about the bear’s age, when the footage was taken and what an autopsy would show. 
 
 Donald Moore, the director of Oregon Zoo, a senior science adviser to Smithsonian National Zoo and an expert on polar bears, said he couldn’t tell much more about the bear’s age or condition from the video except its extreme skinniness. But he said that starvation was one of the results of the polar bear’s loss of icy habitats. 
 
 “These polar bears should be riding ice somewhere,” he said. “We have seen more and more very thin polar bears in the Arctic in recent years as climate change increases in intensity and opens up more water.” 
 
 He said that the population of polar bears in the wild has declined about 20 percent over the last decade or so. Bears need an immense amount of food, he said, about an average of a seal a week. 
 
 Nicklen said that while most people were supportive of the photo, a small percentage had been offended that he had not taken more action by feeding the bear, trying to save it or putting it out of its apparent misery. 
 
 “It’s not like we travel around with 200-300 of pounds of seal meat when we’re walking around in the Arctic,” Nicklen said. “We knew it was going to be gut wrenching and intense and horrible.” 
 
 Cleve R. Wootson Jr. contributed to this report. 
 
 Read more: 
 
 Polar bears hurt by climate change are more likely to turn to a new food source — humans 
 
 The most accurate climate change models predict the most alarming consequences, study finds 
 
 First a polar bear petted a dog. Then a polar bear did what polar bears do: Ate a dog. 
 
 Love in the time of climate change: Grizzlies and polar bears are now mating ||||| The text on the video above was edited on June 1, 2018 to make it clear that it is impossible to know why the polar bear pictured was starving. An earlier version of the video went too far in suggesting that climate change was responsible ( read more ). This story was updated on January 19, 2018 to reflect the more specific location of where the photographs were taken. 
 
 When photographer Paul Nicklen and filmmakers from conservation group Sea Legacy arrived on Somerset Island—near the larger Baffin Island—in the Canadian Arctic in late summer, they came across a heartbreaking sight: a starving polar bear on its deathbed. 
 
 Nicklen is no stranger to bears. From the time he was a child growing up in Canada's far north the biologist turned wildlife photographer has seen over 3,000 bears in the wild. But the emaciated polar bear, featured in videos Nicklen published to social media on December 5, was one of the most gut-wrenching sights he's ever seen. 
 
 "We stood there crying—filming with tears rolling down our cheeks," he said. 
 
 Video shows the polar bear clinging to life, its white hair limply covering its thin, bony frame. One of the bear's back legs drags behind it as it walks, likely due to muscle atrophy. Looking for food, the polar bear slowly rummages through a nearby trashcan used seasonally by Inuit fishers. It finds nothing and resignedly collapses back down onto the ground. 
 
 In the days since Nicklen posted the footage, he's been asked why he didn’t intervene. 
 
 "Of course, that crossed my mind," said Nicklen. "But it's not like I walk around with a tranquilizer gun or 400 pounds of seal meat." 
 
 And even if he did, said Nicklen, he only would have been prolonging the bear's misery. Plus, feeding wild polar bears is illegal in Canada. 
 
 The wildlife photographer says he filmed the bear's slow, beleaguered death because he didn't want it to die in vain. 
 
 "When scientists say bears are going extinct, I want people to realize what it looks like. Bears are going to starve to death," said Nicklen. "This is what a starving bear looks like." 
 
 The Climate Change Link? 
 
 By telling the story of one polar bear, Nicklen hopes to convey a larger message about how a warming climate has deadly consequences. 
 
 Polar bears have long been unwitting mascots for the effects of climate change. As animals that live only in Arctic regions, they're often the first to feel the impacts of warming temperatures and rising seas. 
 
 The large, half-ton bears find concentrations of seals on sea ice. During summer months, it's not uncommon for polar bears to go months without eating while they wait for Arctic ice to solidify. 
 
 In 2002, a World Wildlife Fund report predicted that climate change could eventually lead to polar bear endangerment or extinction. Even then, the report found that polar bears were moving from ice to land earlier and staying on land longer, unhealthily extending the bears' fasting season. By the end of summer, most bears studied by the World Wildlife Fund showed signs of starvation. 
 
 Fifteen years later, polar bears' icy hunting grounds are in even worse shape. The National Snow and Ice Data Center, which tracks sea ice cover annually, has regularly noted record lows in sea ice coverage—a decline that is expected to only get worse. (Read more about drastic predictions for dwindling sea ice.) 
 
 A study recently published in the journal Biosciences looked at how climate science is often falsely discredited. The study found climate deniers are able to downplay the threat of climate change by discrediting the threat facing polar bears.
– An estimated 2.5 billion people saw the image: a starving polar bear struggling across an Arctic landscape. "The mission was a success, but there was a problem: We had lost control of the narrative," writes Cristina Mittermeier in National Geographic. Accompanied by a photographic team, she snapped shots of the dying bear last year while colleague Paul Nicklen shot video—all part of their "mission to capture images that communicate the urgency of climate change," she writes. "When Paul posted the video on Instagram, he wrote, 'This is what starvation looks like.'" He also wondered if all 25,000 polar bears would die like this and urged people to reduce their carbon footprint. But he didn't say climate change had killed this bear. That nuance vanished when National Geographic posted the video with the subtitles "This is what climate change looks like" and the Washington Post ran a dramatic headline about "gut-wrenching" images. People also responded dramatically, expressing gratitude for validation of climate science, anger the crew hadn't fed the bear, or a stubborn refusal to acknowledge global warming. "Perhaps we made a mistake in not telling the full story—that we were looking for a picture that foretold the future and that we didn’t know what had happened to this particular polar bear," she writes. Yet a fast-warming Arctic means bears will be stranded on land, unable to pursue prey, so the photo makes sense. The trick for next time? Make sure "our intentions are clear and the narrative remains our own."