Snow time like present for Revenant director Inarritu

Leonardo DiCaprio stars in The Revenant as real-life explorer Hugh Glass

Oscar-winning director Alejandro G Inarritu faced a number of challenges while making snowbound survival tale The Revenant - one of them being a shortage of actual snow.

In period western The Revenant, a 19th Century fur trapper on the American frontier wages a gruelling battle for survival after he is savagely mauled by a bear and left for dead by his callow fellow hunters.

(The title of the film, as fans of spooky French TV series Les Revenants will know, refers to one who returns from the dead.)

No-one would pretend the makers of Leonardo DiCaprio's latest suffered anything comparable. Yet the film still represented a formidable endurance test for all involved.

Just ask Will Poulter, the 22-year-old British actor who plays the youngest member of an embattled hunting party that also includes Tom Hardy and Ireland's Domhnall Gleeson, of Star Wars: The Force Awakens fame.

"I think for the entire cast and crew it was the hardest thing they've ever done, and possibly the hardest thing any of us will ever do as well," he told the BBC.

"It was gruelling and pushed us far beyond our personal limits, or at least what we initially thought we were capable of, both physically and emotionally."

At one point, the arduous shoot in Alberta, Canada, saw crew members confronted by a blizzard that plunged temperatures down to minus 27 centigrade.

Inarritu (left) was named best director at last year's Oscars for his work on Birdman

DiCaprio, meanwhile, was obliged to be buried in snow, go naked in sub-zero weather and jump into water every bit as bone-chilling as that he faced in Titanic.

Not only that, but the vegetarian star of The Departed and The Aviator was also compelled in one scene to sink his teeth into a raw hunk of bison's liver.

"The bad part is the membrane around it," the star told Variety last month. "It's like a balloon. When you bite into it, it bursts in your mouth."

For director Alejandro G Inarritu, however, an even bigger challenge arose when an unseasonable warm spell saw the snow vanish faster than Michael Keaton's Oscar speech.

(For those who missed last year's Academy Awards, the Birdman star was seen discreetly putting his acceptance speech back into his pocket after being pipped to the best actor award by Britain's Eddie Redmayne.)

"We were victims of global warming," said Inarritu. "Usually there's a huge amount of snow in February but it was almost like summer: historically they registered the hottest winter ever.

"We went to our locations and they were destroyed by just one degree difference in temperature in the months it should not happen."

In the end the production was forced to decamp to Tierra del Fuego on the southern-most tip of South America in order to get the snowy landscapes they needed.

"There was a very big possibility I would not finish the film in time to release it this year," admitted the director, whose previous films include Babel and 21 Grams.

"The conditions and the weather were absolutely madness."

Admittedly, Inarritu and his regular cinematographer - two-time Oscar-winner Emmanuel "Chivo" Lubezki - did not make it easy on themselves.

At an early stage of production, it was decided the film would not only be shot chronologically but would also be illuminated only by natural light or firelight - an aesthetic choice that placed an additional time constraint on an already pressurised crew.

"We had to find the right time of day for our shots and then pray the weather would hold," said Inarritu. "It took a lot of time, thought and rehearsal to get it right.

"One thing is the notion of things and the other thing is the reality of those things. You go into the reality of things and they are normally very different from what you thought."

British actor Poulter was previously seen in Son of Rambow and We're the Millers

"There was a pursuit of perfection right from the off, and it was something Alejandro encouraged everyone to shoot for in every department," said Poulter. "We were out there so long it took an emotional toll on all of us.

"But it was amazing to return to the film approach of old, where you shoot in natural light on location, with real weather elements.

"We were able to work on a level of authenticity that you couldn't recreate in a studio."

One sequence that could not have been done authentically was the harrowing bear attack DiCaprio's Hugh Glass character is subjected to near the beginning of the film.

The bear itself is a computer-generated creation - a detail that was overlooked by The Drudge Report when it claimed the creature had subjected DiCaprio to a sexual assault.

The claim was considered serious enough to merit an official response from the film's distributor, who insisted there was "clearly no rape scene with a bear".

For his part, Inarritu expresses bafflement that such an outlandish story could gather so much traction in such a short space of time.

"How do these things happen? Nobody understands," he told the BBC News website. "It's indescribable how something that absurd can be validated by newspapers.

"It is," the Mexican film-maker concludes, "a crazy world."

The Revenant is out in the UK and Ireland on 15 January.