It was still dark when we finished our snack break and I heaved my rucksack onto my back again. I pulled at the straps as they caught on the puffy sleeves of my down suit and made sure not to get the hose from the oxygen tank trapped, twisted or pulled. I needed that more than ever now.

I was with my Sherpa partner, Tenzing, a bit beyond the South Summit of Mount Everest (figure 1). It was just the two of us – the other four climbers of my expedition team were ascending at their own pace, with their own guides to help them. We were more than 8700 m above sea level and well into the “death zone” – altitudes above 8000 m, where humans cannot survive for long even with a supplementary oxygen supply. I adjusted my connection to the fixed rope leading up the mountain and looked at the route ahead in the beam of my headtorch. It went up steeply in a dramatically narrow path through rock and ice. It was time to start walking again.

At about 4.30 a.m. on 21 May 2018, after almost seven weeks on the mountain and years of preparation, we finally reached the 8848 m-high summit and watched the sunrise from the highest vantage point on Earth. It was incredible. Everything seemed so small. Even Lhotse, the 8516 m peak that had towered over us at Camp 4 on the South Col, now looked tiny. Everest is high, and truly extreme.

Mint cake on the mountain

On 29 May 1953 at 11.30 a.m. Edmund Hillary and Tenzing Norgay completed the first known successful ascent of Mount Everest (see box below). While at the highest point in the world, the pair took photographs, buried sweets and a cross, collected rocks, and ate mint cake – but they couldn’t share their achievement with anyone else. It wasn’t until they returned to the South Col five hours later (it’s much quicker to descend) that the first of their team learnt of the momentous achievement. This small group then tried to signal the rest of the expedition further down the mountain by arranging sleeping bags in a “T” for “top” on a visible snow slope, but clouds blocked the view. Only once they arrived at a lower camp the next day did expedition leader John Hunt finally hear of his team’s success.

The first to the summit

Edmund Hillary and Tenzing Norgay were the first known people to reach the highest point on Earth. They were part of a large British expedition led by John Hunt, involving 12 other mountaineers, 20 Sherpa guides, 362 porters and over 4500 kg of luggage. This ninth attempt by the British was considered their last chance to be the first to the summit; the northern route through Chinese-controlled Tibet was closed in 1949, while Nepal allowed only one expedition a year through the southern route – and France and Switzerland had already booked the next two years.

The expedition took more than a month to get from Base Camp to the South Col (Camp VIII). From there Hunt sent out the first pair of climbers, Tom Bourdillon – a research physicist who had studied at the University of Oxford – and Charles Evans. Although they reached Everest’s South Summit, the pair began to run low on oxygen and were therefore forced to retreat with only 100 m to go.

Next came Hillary and Norgay’s attempt. An advance party went ahead of them to establish an even higher camp, Camp IX, and dropped off equipment and oxygen for the pair to pick up on their way. By the time they reached Camp IX, Hillary and Norgay were carrying 29 kg and 23 kg respectively. The advance party hurried back down the mountain while the pair rested, and at 6.30 a.m. on 29 May 1953 Hillary and Norgay set out for the final, gruelling climb.

My own experience of reaching the summit 65 years later demonstrates just how much has changed since that first expedition. When we got to the top, Tenzing simply radioed Base Camp to update them on our progress while I took numerous photographs with my digital camera.

The simple fact is that technological developments have made it slightly easier for climbers and improved our chances of success and survival. We have more lightweight clothing and equipment, less cumbersome oxygen sets, easier communication with Base Camp and the outside world, improved medical understanding and facilities, and the possibility of helicopter rescue. All in all, Everest is busier, but it is safer.

To date, more than 5000 people are known to have successfully summitted Everest (some multiple times) but almost 300 have died trying – this year alone there were six reported deaths on the mountain and more than 700 summits. But the death rate (the number of deaths per attempt of expedition members above base camp) has been reducing over a period of commercialization, from above 10% at the turn of the 1990s to about 1–2%, or even lower, now.

Sure, some of this improvement in safety is due to better management and greater experience among climbers, but the rest is due to improvements in science and technology.

A dangerous adventure

It was science that first got me seriously interested in the tallest mountain in the world, when five years ago I read Hunt’s book The Ascent of Everest. I began to see that climbing Everest was not entirely a crazy game of Russian roulette and that, approaching it from a scientific point of view, I could investigate the things that now make Everest safer and think about how I could give myself the best chance.

Climbing Everest is not entirely a crazy game of Russian roulette and, approaching it from a scientific point of view, I could investigate the things that now make Everest safer

There is, of course, still risk involved in climbing Everest. The biggest danger is that the human body is not designed to live up there. If you were taken from sea level and dropped at the summit of Mount Everest you would be unconscious in a matter of minutes and die shortly afterwards because your body would not be getting enough oxygen to function properly. While the percentage of oxygen in the air at altitude is the same as at sea level – 21% – the air pressure is reduced at the top of Everest to just 34 kPa compared with 101 kPa at sea level. A lungful of air on Everest will therefore contain fewer molecules than at sea level.

Acute mountain sickness (AMS) is caused by low oxygen levels at altitude and kills climbers every year. It presents in a range of symptoms that resemble flu, carbon-monoxide poisoning or a hangover, but can be countered by descending immediately. In extreme cases, however, the body can react by accumulating fluid in the lungs (a high-altitude pulmonary oedema) or creating swelling in the brain (a high-altitude cerebral oedema), both of which can be fatal. Fortunately, as anyone who has gone up a mountain to use a telescope will attest, the body can adapt to use less oxygen. This does, however, take time and you don’t know until you try whether or not your body can adapt. That’s why climbers ascend slowly, ascend and descend in a shuttle-like fashion, and spend days at a time acclimatizing at the various camps at different altitudes.

Then there’s the weather. Obviously, it’s cold on Everest, with the summit never rising above –10 °C. The elevation also means it’s in the jet stream so it is buffeted by unpredictable winds that are above 160 km/h for most of the year. March sees the jet stream begin to drift north, and by May there are just a few weeks that are safe for climbers, with winds below 55 km/h. At this time of year, the summit temperature averages about –25 °C. Frostbite and hypothermia are a real danger, but there’s also the possibility of eye damage and sunburn from the sunlight and ultraviolet rays reflecting off the snow.

One of the most deadly parts of Everest is the summit ridge, the steep section between the South Col and the summit – the last day’s push. This is in the death zone. The body is wasting away, and you have to do a steep, demanding climb. Even with supplementary oxygen you are asking a lot of your body. Some people push too hard and collapse exhausted, never to get up again; some die from accidents, such as falls; some will succumb to AMS; and some get caught in bad weather.

The other most deadly part of the mountain is further down – the Khumbu Icefall. Here the glacier makes a rapid descent, splitting and cracking into a tumbling obstacle course of ice blocks and crevasses. Along with the danger of a climber falling into a crevasse, or ice dislodging or collapsing, there is also risk from above. The steep mountain walls to either side collect thick deposits of snow and ice, which occasionally fall on climbers. In 2014 some 16 Sherpas were killed in this way and the mountain closed for the season.

While some of these dangers are unpredictable, it is possible to reduce the risk surrounding others. Two key factors that have helped increase safety on Everest are improved weather forecasting and communication methods, but developments in medicine, helicopter rescue, oxygen systems, clothing and equipment have also made a difference.

Forecasting a safe trip

Climbing Everest is a risky business and you need almost a week of clear weather to avoid adding storms to the list of dangers. Thankfully weather forecasting has significantly improved due to advances in computer processing power.

The weather models that describe and evolve atmospheric and oceanic processes are hugely complex and necessarily require simplifications, approximations and compromises between scale and resolution in order to run. Increased computer processing power means more calculations can be performed per second so that models can incorporate greater detail or run in higher resolution.

Three decades ago the UK Met Office’s supercomputer was only as powerful as a modern-day smartphone, but their current supercomputer does 14 thousand trillion calculations per second. Better representation of weather patterns means predictions can be made further into the future with the same accuracy – the four-day forecasts nowadays are as accurate as the one-day forecasts of 30 years ago.

Mountain weather forecasting is particularly challenging. Rising, cooling air leads to clouds and rainfall; temperature – which can be fairly stable across a large flat area – drops quickly with increased altitude; and winds swirl and travel through the valleys, often moving the building clouds with them. But comparing forecasts can help. As Victor Saunders, a mountain guide on our team, commented: “The general rule is that if they all agree then you probably have a correct forecast.”

For climbers in the world’s highest mountains the improved forecasting accuracy over a longer period is a big advantage. My summit team of four took six days to get from Base Camp to the summit of Everest and back (we had two rest days at Camp 2 for logistical reasons). Accurate predictions stretching several days ahead ensured we had a sufficiently long window of good weather to make the climb safely.

Staying connected

Communication between camps and climbers on the mountain is also incredibly important, not just for monitoring progress and safety (and sometimes for co-ordinating rescues), but also for organization. Camps have to be set up; food, fuel and oxygen need to be carried; and ropes need to be fixed. All of these things are co-ordinated from Base Camp via radio. Thankfully, radio sets have become much lighter than the “walkie-phone” that was carried between camps in 1953, which weighed 2.3 kg – now we have handheld radios that are less than 500 g.

Climbers also have satellite phones, and there is even mobile phone signal and WiFi at Base Camp (albeit subject to variations in reliability). On peaks more remote and inaccessible than Everest, or after natural disasters such as the 2015 Nepal earthquake, satellite phones can mean the difference between life and death when a rescue needs to be initiated. They can also boost a climber’s morale, allowing them to keep in touch with loved ones back home. When Tenzing and I got back to Camp 4 at the South Col I called my father on the satphone and the signal was brilliant.

The miniaturization of electrical components and advances in materials for clothing and equipment have helped reduce the weight of the loads that climbers need to carry

The miniaturization of electrical components and advances in materials for clothing and equipment have also helped reduce the weight of the loads that climbers need to carry. This is important because, in the mountains, speed is safety, and heavy packs dramatically slow climbers down. We still carry quite weighty bags, but they are far lighter than those of the 1953 expedition. My pack was around 15–17 kg at most and on summit night it was under 10 kg. Climbers have even been known to snap toothbrushes in half or cut labels out of clothes to save weight.

We can also thank developments in materials – particularly microfibres for wicking sweat away from the body. Merino wool does this naturally but synthetic fibres have also been developed – indeed sometimes the natural and synthetic are blended to get the advantages of both. There are also Gore-tex membranes that are waterproof and breathable – so keep out big droplets of water but can let out individual molecules through tiny pores – as well as better-quality down with high warmth-to-weight ratio.

Descending for the last time through the treacherous Icefall, climbing down ice blocks and crossing crevasses by balancing on ladder rungs in spiky crampons, I felt that these ladder crossings became more uncomfortable – more scary – than they had been previously. Perhaps, as I neared the end of the adventure, the mental barriers that I had put up were fading. I just wanted to get down, to get home. All the time I was on Everest I would tell myself to hold on – just one more month, just one more week, one more day. For all the improvements in technology that have made Everest a little bit safer, a little bit easier, your psychology can still be the difference between success and failure. Getting to the highest point on Earth is still a mental game.

• Melanie Windridge made Science of Everest videos for the Institute of Physics and will be giving public talks about her climb. For more information check out melaniewindridge.co.uk/a-journey-of-discovery
• Enjoy the rest of the September 2018 issue of Physics World in our digital magazine or via the Physics World app for any iOS or Android smartphone or tablet. Membership of the Institute of Physics required