A video of an emaciated polar bear on iceless land has highlighted starkly the drastic effects of climate change.

The video, shot by National Geographic-contributing photographer Paul Nicklen and filmmakers from a conservation group called Sea Legacy, shows the starving animal making its way with difficulty across the terrain.

The clip, which was shot in Canada's Baffin Islands, drew comments from thousands of users who called the video heart-breaking.

Mr Nicklen posted the video on his Instagram page on Wednesday (Dec 6), and it has since gone viral with more than a million views.

The sight was one of the most gut-wrenching ones he has ever seen, The National Geographic said in a report on Thursday.

"We stood there crying - filming with tears rolling down our cheeks," he told the magazine.

Polar bears are classified as vulnerable, with a population of 22,000 to 31,000, according to worldwildlife.org.

They were listed as a threatened species in the US under the Endangered Species Act in 2008.