Paul Nicklen introduced the world to a dying polar bear last week, via a viral Instagram video, and Cristina Mittermeier now says posting the video was the only thing they could do to help.

Mittermeier was present with Nicklen, both co-founders of the conservation group SeaLegacy and both photographers for National Geographic, when they saw an emaciated polar bear digging through a can of waste for its next meal.

Nicklen's Instagram post has clocked nearly 1.4 million views since he posted it last week, and Mittermeier has opened up in a first-person account of the experience in National Geographic.

"There is nothing worse for someone who loves wildlife and nature than to witness the suffering of an animal," she wrote in the magazine. "Weak muscles, atrophied by extreme starvation, could barely hold him up. It was clear that, even if I had fed him the handful of nuts I had in my backpack, without sea ice from which to hunt, his prospects of survival would be slim."

Bear scavenged and found trash

The video shows the polar bear eating from a barrel. The video doesn't say what the barrel is — perhaps a spent oil or gasoline drum — but Mittermeier could see what it was.

Trash.

"He chewed on a piece of burnt foam from a snowmobile seat that he found in the trash bin, and I fought back the anger and sadness I felt watching this once-majestic animal reduced to foraging for trash," she wrote.

What she saw is at the heart of the U.S. Fish and Wildlife Service's January update to its conservation management plan for the polar bear, which largely lays blame at the feet of human-caused global warming.

Warming temperatures have eroded polar bear habitats and made it difficult for the ice-dependent bears to hunt, according to the FWS plan.

"The single most important achievement for polar bear conservation is decisive action to address Arctic warming," it says. "Short of action that effectively addresses the primary cause of diminishing sea ice, it is unlikely that polar bears will be recovered."

The shrinking ice cover greatly limits the polar bears' access to their main source of food — seals. Without seals, the bears often have to travel to human settlements and forage for any food they can find, according to the National Geographic report.

Mittermeier acknowledged that she can't be entirely sure what led to the bear's starvation. Maybe global warming led to its starvation, maybe it didn't, she wrote.

"Although I cannot say with certainty that this bear was starving because of climate change, I do know for sure that polar bears rely on a platform of sea ice from which to hunt," she wrote in her National Geographic piece. "A fast-warming Arctic means that sea ice is disappearing for extended periods of time each year."

'We can no longer afford to look away'

In Canada's Baffin Islands, Mittermeier and her colleagues saw what they believed to be the effects of starvation. They were watching a half-ton animal picking through garbage to substitute discarded foam for seal meat.

Online, they were watching comments come in, criticizing them for not doing more to help the bear in that moment.

Along with the accusatory comments, there were also many supporting the polar bear and expressing empathy for its plight.

"Some have criticized us for not doing more to help the bear, but we were too far from any village to ask for help," Mittermeier wrote. "And approaching a starving predator, especially when we didn't have a weapon, would have been madness."

She and her colleagues knew that anything they did in that moment would be a slapdash, temporary fix.

So they opted to record the bear and share its story with millions.

"In the end, I did the only thing I could: I used my camera to make sure we would be able to share this tragedy with the world," she wrote. "I know this image is disturbing and I know it is hard to watch, but we have reached a time in the history of our planet in which we simply can no longer afford to look away."

Environmental coverage on azcentral.com and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental reporting team at OurGrandAZ on Facebook, Twitter and Instagram.