Just before reaching the summit of Mount Everest, Australian engineer Jason Kennison told his mum in a FaceTime call that he would see her when he got back.
He was fulfilling a lifelong dream to stand on top of the world and raise funds for his favoured charity, Spinal Cord Injuries Australia.
But that static-filled video call was the last time Gill Kennison would see her son alive. As the 40-year-old descended from the summit, he caught high-altitude sickness and died.
Kennison is among 12 confirmed fatalities from the spring climbing season, one of the deadliest in recent years. It has just concluded but five mountaineers remain missing. The deaths already exceed the 11 lives lost in 2019, when overcrowding on the picturesque yet treacherous terrain was highlighted by a viral photo of one long queue to the summit.
This year's victims succumbed to the perennial risks of climbing Everest - three Sherpas died in a serac or ice fall, and the others fell ill like Kennison.
But the high number has renewed scrutiny on overcrowding after a record number of climbing permits were issued in Nepal, and deepened concerns about the impacts of climate change on the mountain.
Locals in Nepal - the most popular jump-off point for climbers - attributed the unprecedented 900 permits to pent-up travel demand from the pandemic.
Having so many people puts pressure on "traffic jams" on the climbing route, Garrett Madison of US-based Madison Mountaineering company told Reuters news agency.
Lines form when mountaineers need to catch a window of favourable weather to reach the summit. They need to avoid jet streams or narrow bands of strong wind in the upper atmosphere. Queues can also be held up by inexperienced and unprepared climbers.
Extremely thin air on peaks higher than 8000m makes it difficult to breathe and climbers often use oxygen canisters to survive, but logjams put pressure on supplies.
High altitudes can cause the body to produce excess fluid and cause swelling in the lungs and brain. This can lead to fatigue, breathlessness, and loss of co-ordination.
Adrian Ballinger of US-based Alpenglow Expeditions, which leads climbers from the China side, said some companies from the Nepal side have been taking climbers to Everest even if they do not have enough experience to navigate the death zone.
Everest expeditions are a major source of income for Nepal, whose government is often criticised by some Western climbers for allowing anyone who can pay the US$11,000 ($18,000) fee for a permit to go up. The government denies this.
On top of the permit, each climber spends at least $26,700 on an expedition in Nepal, including on permit fees, gas, food, guides and local travel, according to sherpas.
Yubaraj Khatiwada, director at Nepal's Department of Tourism, rebuffed criticism of the number of permits awarded. Speaking last month, he said a team of doctors and government officials would be stationed at the Everest base camp for the first time to manage climbing activities throughout the season.
"We are concerned for their safety and are well prepared to cope with the crowd, by spreading summit bids as long as the good weather window provides to ensure the climbing goes smoothly as far as possible," Mr Khatiwada told AFP.
Lukas Furtenbach, whose Austria-based tour company has brought 100 people to the summit since 2016, stressed the need for readily available oxygen, given the threat of overcrowding. He said his company has measures in place to make sure that their clients never run out of oxygen and that they have recorded zero accidents.
"Proper oxygen logistics are super important if there are many people climbing at the same time. I am convinced that with minimum safety, equipment and logistic standards for all operators, we could avoid many of the deaths that happen today on Everest," he told the BBC.
While this year has seen no deaths due to avalanches, these events have accounted for roughly 40 percent of fatalities in recent years, according to The Himalayan Database.
An avalanche in 2014 killed 16 people, in what is considered the worst accident on the mountain in modern history.
Climbers have also had to contend with warmer temperatures, that have melted glaciers and caused lakes to form. Scientists noted that due to climate change, temperatures on the Tibetan Plateau, where Everest is located, have increased by around 2C over 40 years from 1979.
And when the snow melts, glacier ice loses its cover from the sun, causing it to either turn into water that goes down the slopes or vaporise into the air due to strong winds, according to research published in 2022 by the University of Maine's Climate Change Institute.
Climate effects will "change the experience" of Everest climbs as more bedrock is exposed in place of snow and ice, and icefalls and avalanches become more "dynamic", the study said. Melting glaciers could also "destabilise" base camp that houses about 1000 climbers and logistics team during the peak season.
But plans to move the camp have been recently shelved. Last month, Sherpa leaders told the BBC that proposals to shift it were impractical.
The changing terrain has been jarring for guides who have traversed the area for years.
"They're saying that every time they go back, the mountain looks different. So where there used to be ice last year, there's water, where there used to be hard snow, now it's soft snow," veteran guide Pasang Yanjee Sherpa said in a podcast after the 2022 spring season.
This year saw unusual snowfall that normally occurs during the winter months, Ang Tshering Sherpa, former president of the Nepal Mountaineering Association, told AFP. This heightened the risk of an avalanche since fresh snow is soft, he said.
For Furtenbach, climate change impacts seem "remarkable and never seen before".
"I assume that for the next five to 10 years, we will slowly start to see if and how the climbing route on Everest will be affected by global warming," he told the BBC.
Lure of summit remains
The season has also seen dramatic rescues and milestones. Last month, Nepali guide Gelje Sherpa carried a Malaysian climber down from 8,500m above sea level over the course of six hours.
Separately, Kami Rita Sherpa from Nepal reached the summit for a record 28th time, solidifying his reputation as the world's "Everest Man".
And earlier, Hari Budha Magar, a former Gurkha soldier who lives in Britain, summited Everest with prosthetic legs. He is the world's first double above-the-knee amputee to achieve this feat.
Misfortune and triumph just days apart shows the need for rigorous preparation to conquer Everest and survive in the most hostile conditions, experts say.
"Tragedy, deaths and drama play a vital role why people are drawn by Everest. It is the highest point of this planet, but also one of the most dangerous places on earth. This combination attracts people," Furtenbach says.