It may not be obvious from his tall, sturdy frame but Tim Jarvis has been starving himself.
The explorer and environmental scientist put on an altitude mask to deprive his lungs of oxygen to prepare for his ascent of three mountains in Ecuador including Cotopaxi, a 5897-metre active volcano whose summit is off-limits due to the threat of imminent eruption.
"I sit there for maybe half-an-hour in the morning, half-an-hour in the evening," Jarvis says. "I stick on the mask and turn it up, in the old money, to 18,000 feet, which is just shy of 6000 metres and sit there and read the paper.
"It's hard doing it but it starts to get you accustomed to the level of breathing difficulty you get at that altitude."
The strain on his cardiovascular system is not the only challenge Jarvis endured during the mountaineering expedition, part of his 25zero project that aims to bring attention to climate change by highlighting melting tropical glaciers.
Starting off in malaria-infested tropical jungles, Jarvis coped with dramatic changes in temperature as he climbed the mountains: "That takes a toll on the body particularly when you're doing it in a short time frame."
But it was a small price to pay compared to the hardships that may be suffered by the inhabitants of Ecuador who rely on the seasonal melt of glaciers to provide up to 25 per cent of their water supply. Cotopaxi's glacier will vanish in 21 years, according to the 25zero website, but other mountains in Ecuador have already seen glaciers completely melt.
Jarvis launched 25zero during the Paris climate change talks in 2015, scaling mountains in Africa and Asia to show how the melting of glaciers will lead to water shortages that could affect millions of people.
"People are a little bit bored of hockey-stick curves, Al Gore-style information," he says. "I'm trying to find content which is different and interesting for people where they might actually think, 'Wow, I didn't know there were any glaciers at the equator'."
Jarvis is also critical of the methods used by environmental campaigners, which he says often alienate sections of the community.
"I think we've often used guilt and fear too much with respect to the environment," he says. "We need to be more aware of the fact that different people are moved by different things."
Jarvis takes a pragmatic approach of using whatever argument - economic, moral, political - it takes to persuade decision-makers to take action on climate change.
"It doesn't mean I'm not green as hell," he says. "I am. Frankly, I get disappointed when people are not moved by the moral arguments: the future of the planet, the animals and plants we share it with, our kids and everything else. Sadly not everybody is moved by that."
He is not impressed by the Turnbull government's national energy guarantee plan: "Energy security is being used as the reason to support fossil fuels for longer to placate certain interests, which is also bad and I'm afraid indicative of current Liberal politics."
Jarvis has undertaken expeditions to the world's remote regions, including crossing the Great Victoria Desert and journeys to the North and South Poles.
In 2006, he retraced Sir Douglas Mawson's 1912-13 Antarctic trek using century-old equipment and surviving on starvation rations.
The expedition killed Mawson's fellow explorer Belgrave Ninnis, who fell into a crevasse with much of their food and equipment, and Xavier Mertz, who died during the desperate journey back to home camp.
David Day's 2013 book Flaws in the Ice suggested Mawson, who appeared on an earlier $100 paper note, may have boiled and eaten Mertz - an account disputed by Jarvis, who says he survived the journey without resorting to cannibalism.
However, he says, half-joking, that fellow explorer John Stoukalo became increasingly nervous during their 2006 polar journey. "I said in the event it can't be done with the food Mawson said he had, there may come a point where I have to eat you," Jarvis says.
Human flesh is thankfully not on the menu at Flying Fish, Jarvis' choice of lunch venue. The waterfront restaurant's Asian-influenced seafood dishes are a far cry from the menu on any of Jarvis' epic journeys.
"Expedition food is normally the low point of any trip," he says. "On big polar trips it's all about eating fat, vast amounts of fat, because it gives you the calories you need and it's the least weight you can carry for the calorific return."
If he is not fortifying himself with congealed animal fat, Jarvis prefers olive oil for his Antarctic adventures.
"You see hospital dramas where they have the big drip bags?" he asks. "I took 90 of those on my South Pole trip and you just melt one of those when you need to eat. It freezes solid and you just pack it in your sled."
Jarvis embarked on another epic polar expedition in 2013, retracing Sir Ernest Shackleton's 1916 crossing of the Southern Ocean before clamouring over South Georgia Island's mountainous terrain using the gear and equipment from the famed British explorer's era.
It was this journey that drew his attention to the dramatic retreat of glaciers. "A third of glaciers which for [Shackleton] were a huge physical barrier were for us lakes we had to wade across," Jarvis says.
Both polar expeditions inspired documentaries and books. A polymath, Jarvis is also a public speaker - turning his expedition experiences into lessons on leadership to corporate types. He sits on countless boards, works as a sustainability advisor for the World Bank and Asian Development Bank and has a day job with engineering firm Arup. He was awarded an Order of Australia (AM) for services to the environment, community and exploration in 2010 and was chosen as the Australian Museum's "trailblazer-in-residence" and included as one of Australia's 50 greatest explorers in the 2015 Trailblazers exhibition.
He is also a spruiker for outdoor clothing manufacturer Kathmandu and a brand of Scotch malt whisky named after Shackleton.
Jarvis, who lives in Adelaide with wife Elizabeth and his sons William, eight, and six-year-old Jack, developed a taste for adventure during his childhood in Malaysia where his father was the accountant for the company that distributed Tiger Balm.
In an era before the internet and helicopter parenting, his parents would dispatch him from the family home, telling their son: "Off you go, discover things for yourself."
The young Jarvis formed an adventure club. "There were no members apart from me but I used to carry a compass with me routinely as part of the kit I thought an explorer would have."
Jarvis' navigation skills were put to the test as a 12-year-old when he was among a group of school children who became lost in the jungle while on a school trip. He pulled out his compass, determined where north lay and began "bush bashing".
"Many hours later, after nightfall, I got out onto the coast and headed in what I thought was the right direction for camp where all these teachers were panicking, thinking they'd lost these kids forever," he says.
Jarvis says his boys have already expressed an interest in joining his expeditions. "They are making noises," he says. "I encourage them to live life adventurously regardless of the discipline; i.e. it doesn't have to be climbing or polar trips."