Minus 70 degrees Celsius, out on the polar ice.
How does anyone survive in conditions like that? We are sitting in the lounge of Craig Mathieson's Bo'ness home, surrounded by books on the explorer's heroes, when this question arises. In this domestic setting, with children's voices to be heard from the back of the house, it is difficult to imagine the solitude, the whiteness and the physical challenge of being on the ice, but it is never far from Mathieson's mind.
Ten years ago, the man who is now the Royal Scottish Geographical Society's explorer-in-residence, mounted the first Scottish expedition to the South Pole, an ambition he had nurtured since he was 12. He went with a colleague, Fiona Taylor, but on the first night, the worst Antarctic weather in 15 years hit. It was -51C in the tent and -18C inside Mathieson's sleeping bag. Hypothermia set in for Taylor and they had no choice but to struggle back to a logistics base. Once there, it took several hours just to warm Taylor's hands enough to remove her gloves. She recovered, but could not continue with the expedition and so, on day five, Mathieson set out for the Pole as the only Scot in an international team of five. And then it got colder. So how on earth did he keep warm?
"I can adjust my heart rate up and down, so the colder it gets I can think about heating my hands up and they go hot because I just speed my heart rate up," offers Mathieson. He says this as if explaining how his camping stove works. Catching my incredulous look, he smiles. "This is something I genuinely thought everyone could do," he says. "It's something I grew up with. I remember the kids at school thought I had antifreeze instead of blood because we'd go out playing in the snow in Buchlyvie and I would come in and my hands would be glowing red with heat."
If this seems an astonishing capability (it's one thing for frogs and crocodiles, quite another for wee lads from Stirlingshire), it is the only time during our conversation when Mathieson, 45, reveals that there might be something a bit special about him. As a rule, he is fiercely lacking in ego, an attentive listener with quiet manners, but at the same time, a man of rare determination. As well as reaching the South Pole (in 58 days), the father-of-three and former Royal Navy seaman who saw active service in the first Gulf War has also been to the North Pole, but he firmly believes that you don't have to be an action hero to do a polar expedition.
He's no celebrity adventurer angling for a media career and no braying tough guy with an inflated sense of his own importance. People of that ilk do not impress him. By his own admission, he is the painfully shy boy from school who had a dream and turned it into reality. And now he has given up his job as a tax accountant to dedicate himself to inspiring confidence and self-belief in other quiet kids, by taking them to the Arctic.
Mathieson has set up the Polar Academy, through which he is choosing 10 teenagers, this time from North Lanarkshire, to go on a trip to Greenland. It is specifically the shy souls he wants - not the high achievers and sports aces, and not the disruptive children for whom there are numerous initiatives, but the ones in the middle, who drift through the system. "They are forgotten about, invisible. They never achieve great things, but they never get into any great trouble and they usually leave school at 16 or 17 and do exactly what their parents have done." Going into the schools, he sat down with the teachers and support staff, and went through the children's profiles. The ones who hadn't spoken in years went to the top of the pile.
He has utter faith in these children because he knows how it feels to be them. "I just didn't fit in at school at all," he says. "I just stared out the window for four years. I was absolutely one of these kids, but I was a feral child as well. I would go camping by myself at weekends.
"I remember my guidance teacher when I was 16 saying: 'Right, what are you going to do with your life?' And I said I'm going to be a polar explorer and she just laughed and said 'People like you don't do stuff like that'. But even at 16, I knew that was wrong."
Mathieson's love affair with exploration began when his primary head teacher gave him a book, The Worst Journey In The World, about Captain Scott's South Pole expedition. He still has it. He developed an abiding respect for Scott ("an absolutely fantastic leader of men"), Shackleton and the professionalism of the great Norwegian Roald Amundsen, who beat Scott in the Antarctic. He admires many contemporary Norwegian explorers, such as Rune Gjeldnes. Mathieson is now sponsored by high spec Norwegian outdoor gear makers Bergans, who have a history of supporting explorers and are sponsors of the Polar Academy.
"Amundsen had a brilliant saying, 'an adventure is just a badly planned expedition,' and that's what I follow as well," he says. "Expeditions are about hard work, training, discipline, listening to others and then a stack of luck. For me, exploring is about privilege. It's a privilege just to set foot in the Arctic."
He also appreciates the solitude. When he discusses life in central belt Scotland, a word recurs: chaos. It's chaos here, he says, but out on the ice, there's "clarity".
This may also help explain why he sees such potential in quiet people. Those with egos, he declares, should go and be rock stars.
What about women? I wonder aloud. I'd always assumed that because women tend to be weaker and more likely to have circulation problems (slim women are prone to Reynaud's phenomenon, when the fingers go white in the cold due to lack of blood), it must make polar exploration tougher for them.
This is the first - but not the last - time that Mathieson gently challenges me over a "can't do" statement. He smiles. "Not at all," he says. "Women are physically better at it than blokes."
Better, really? He tells me about Denise Martin, a Reynaud's sufferer who made it to the South Pole the same year as him. Apparently if you freeze your hands round your poles, and avoid frostbite, you can trek to the Poles with Reynaud's.
Mathieson laughs. "The thing I think it comes down to - and I love this - is that women don't whinge as much as blokes. They just get on with it. I know the blokes are going to exaggerate their fitness and the women are going to underplay their fitness. Blokes tend to remind you that they are cold and hungry.
"It's just far easier to do a trip with women than with blokes. It's a lot more relaxed, you get bigger mileages done and camp routine is quicker. If you are taking six Alpha males out, it's a nightmare, and you just feel like smashing their heads together." Fair enough.
He certainly takes his own training very seriously. After we chat today, he is heading out to woodland to drag tyres around, to emulate pulling a sledge in snow (he can spend nine hours a day doing this for weeks before an expedition).
He also trains himself mentally. So how did he handle the voices in his head during his South Pole trek? "I just changed them. I would bring my kids into it and they would be walking along, beside me, just out of view. It sounds nuts, but they would be egging me on, telling me to ski faster, take fewer breaks, you don't need to sleep that long."
He used that mental discipline to tackle the relentless hunger, it being impossible to carry sufficient food on the sledge. He would remember being a little boy and trying to eat three large Easter eggs in one sitting. The memory was so powerful, he would feel sick.
Mathieson doesn't do danger. He says the most dangerous situation he has been in was being jumped by two guys at Dunfermline bus station (apparently they regretted it). But in the South Pole, there was no avoiding the crevasses. To cross them required a snow bridge, an arc formed by a snow drift that extends across the gap. "There were a few hairy moments where the snow bridge was an inch narrower than your sledge and you're going across and there's bits falling off. I've done a few of 400m depth where it's just black when you look down." He grins. "You are happy when you get to the other side." An understatement, perhaps. But if he had any doubts about a bridge, he would just find another, even if it meant trekking five more miles. "You don't take any risks on trips at all, it's not worth it."
In the Arctic, of course, there is the theoretical threat of polar bears. Three years ago, an Eton schoolboy was killed by a bear in Norway, though that was in Svalbard, known to be frequented by bears.
Mathieson says the chances of his group seeing a bear in Greenland are very slim - he has never seen one in the 15 years he has been visiting - but he will be taking no chances. They will sleep with a loaded rifle. "You are travelling like Fort Knox. We have double trip wires, people on watch and on this particular trip with the kids, we are taking drones with thermal imaging cameras that we can send up and scout for 3km round the camp. The reality of it is you've probably got more chance of an attack by a pine marten at the front door, but you've got to be prepared just in case."
With polar bears being a threatened species, the first priority must surely be to avoid situations where they may have to be shot? "Yes, that's the absolute last resort." On the other hand, the area they are visiting is surrounded by hunting communities that will shoot bears on sight. "They'll kill everything. If one comes down it will probably be dead 100km before it gets to us."
Mathieson has taken teenagers to the polar regions before. He even reached the North Pole with one chronically shy boy. "The idea was to show him he could achieve anything." He has now become the first person in his family to graduate from university and his parents have made big changes in their own lives, which they put down to being inspired by their son's Arctic trip. That's what the Polar Academy is about - far more than showing some kids the northern lights.
A couple of weeks after we chat, I get a call from Mathieson, who has held his first selection weekend for 10 children and 10 parents from Coltness High School at Glenmore Lodge near Aviemore. He is tired but elated.
Though nervous on arriving, the group spent the weekend tying knots under water, climbing, abseiling, kayaking, orienteering, hillwalking and finally giving presentations on why they felt they should be selected - all with a documentary film crew in attendance.
"It was just a rollercoaster," Mathieson says. "These kids' lives are already changing, and their parents'. There were a lot of tears, as you can imagine. Some of them had had no good news, period, in their lives. It was heart-melting, it really was." He speaks of children in whom he saw absolute greatness, but who have no idea of their potential. Yet.
He would like to take everyone, but cannot. However, those who are not picked will remain members of the Polar Academy with other important responsibilities and will be on the reserve list. The five who go through will be joined by another five from St Aidan's High in Wishaw, chosen from another selection weekend in July, and the trip will take place in April next year.
It has the potential to be life-changing, but he still needs more precious funding.
"There's so much riding on it now." n
The Polar Academy is supported by donations and sponsorship. The Polar Academy 180 initiative involves donating a least £1000 a year for three years. To contribute, go to thepolaracademy.org. All donations welcome.