Josh Hartnett takes a cold punt on the real world in 6 Below

There was a moment when Josh Hartnett was filming his new film 6 Below – the true tale of Eric LeMarque, an American snowboarder and former Olympic ice hockey player – that he realised just how close to reality it was. Hartnett was on the second day of the shoot in a mountain range near Salt Lake City when the crew spotted a girl who had got separated from her party . She had been walking for two hours in the wrong direction. "It just blew my mind that this sort of thing happens," he says. "If she started to lose track of which direction she was heading, or if it got dark, or she was not able to navigate by the sun, she would've been in really deep trouble. Her phone wasn't working, there was no signal back there … that was the moment I realised this stuff is still real and relevant. If you're stuck on the wrong side of the mountain, you're in trouble." In the case of his character, LeMarque was snowboarding on California's Mammoth Mountain in 2004 when a huge storm hit and he found himself stranded. What followed was a miraculous survival story as LeMarque stayed alive for eight days on the mountainside until the National Guard managed to pick up a signal from his equipment. "I couldn't believe the level of strength it must've taken," says Hartnett. "Not many people could survive in conditions like this for more than a couple of days." While the film suggests that LeMarque's hallucinogenic state on the mountain led him to find clarity about his personal issues – not least an addiction to drugs – and give him the strength to survive, there is no question he was in dire straits. Without food, he ate bark and pine needles and found a water source, which just about sustained his weakening body. His feet turned black and purple with frostbite and later had to be amputated . "That's about as bleak as it gets!" Hartnett, 39, has played in previous big-scale films that took him to extremes – notably Michael Bay's wartime drama Pearl Harbor and Ridley Scott's Black Hawk Down , which chronicled a 1993 US military raid in Mogadishu. He even starred in 30 Days of Night , a vampire movie set in snowy Alaska, although it was actually shot in New Zealand. "The snow was a toxic mixture of Epsom salts and shredded paper," he grins. "This was real snow [in 6 Below ] and probably a lot less terrible for my long-term health!" After spending three years in Dublin, "in a nice, warm cosy studio", shooting the series Penny Dreadful , Hartnett was craving another outdoor experience. "I felt like it would be fantastic to take on the elements … the pressure and the challenge of being the only actor [in a lot of the scenes] was exciting ... "For most of the shooting schedule, I was on the mountain by myself with the crew. And that felt like a challenge I couldn't pass up." Hartnett grew up in Minnesota, so the cold comes naturally to him. But even he began to suffer on a production that required snowmobiles to take a small crew to the shooting locations. "At one point, I had the beginnings of frost bite and we had to stop filming for a little bit and I had to warm up. The medics wanted me to stop for a couple of days while my feet would thaw but it wasn't possible." The solution? Breakable heat pads placed in his boots. With his partner, the English actress Tamsin Egerton, in tow, Hartnett can hardly have been much fun to be around. "I would come home at night and sit in the bath. Literally. My muscles were so sore from all the hiking. At altitude, everything is more difficult. We're up at 10,000 feet [3,050 metres] or more; that's high enough that when you come down at the end of the day, you're feeling fatigued. I couldn't do anything. I just had to get in the bath, take a melatonin, go to sleep, wake up before dawn, get back on the snowmobiles and get back out there." Certainly, 6 Below is well timed, arriving at a moment when Hollywood is taking a punt on shooting films in extreme conditions. The Oscar-winning The Revenant , with Leonardo DiCaprio, jungle adventure The Lost City of Z and Christopher Nolan's Dunkirk have been followed by the recent plane-crash drama The Mountain Between Us , with Kate Winslet. "We decided to do this before The Revenant had come out," says Hartnett. "In a way if The Revenant hadn't done so well, it would've been more of an uphill climb for us." As the actor puts it, audiences are craving films shot in real-world environments, rather than against green-screen backdrops with the landscapes added in later by CGI. "I think people can feel it [when it's been shot for real]," says Hartnett. "Also people are interested in these stories of survival now. They seem to be popping up left and right in the world." In our increasingly urban lives, with GPS tracking our every movement, it's no surprise that we fantasise about pitting ourselves against Mother Nature. With 6 Below directed by former stuntman Scott Waugh, who previously made the authentic Navy SEALs drama Act of Valor , Hartnett felt it was essential that he put himself through these extreme conditions. "The thing I kept going back to, if we were going to do it well, if it's going to make people squirm or make people understand what Eric had gone through, I needed to be exposed to those elements and there's a responsibility to it, so it didn't bother me." Hartnett has no immediate plans to return to such a hostile environment. With two small children with Egerton – dividing his time between the UK and the US – he is quite content to stay at home with "the brood" as he calls them. "We're much more stable now than I've ever been. That travelling lifestyle has slowed down a bit and I'm spending less and less time on the road," he says. "I'm nearing 40 … it's about time I started growing up." 6 Below opens today in UAE cinemas _______________ Read more: Oscar nominee Jim Sheridan: Arab film makers should stop chasing Hollywood _______________

Josh Hartnett takes a cold punt on the real world in 6 Below

6 Below is a well-timed arrival, a true story about how an Olympic ice hockey player survives stranded in a snowstorm, writes James Mottram