Nepal and China have reached an agreement that Mount Everest - known as Sagarmatha in Nepal and Chomolungma in Tibet - is 0.86 metres higher than previously calculated in 2005, standing at 8,848.86m. The recorded height of the world's highest peak had previously differed following surveys by the two countries. China's calculation of 8,844.43m was four metres lower than Nepal's measurement, due to differing opinions on whether to include the snow cap or not.
This is the first time that Nepal has sent its own surveyors to measure the mountain, having previously relied on the 1954 Survey of India.
The decision to jointly announce the new height was reached during Chinese President Xi Jinping's visit to Kathmandu last year.
Everest rises about half a metre each century due to plate tectonic collision between the Indian and Eurasian plates. Surveyors have long argued over whether to include the changeable snow cap - which is believed to have diminished in the time between this measurement and the previous in 2005 - or to measure up to the rock.
An equally important and often trickier issue, however, is the matter of what point to measure down to in order to carry out trigonometric calculations to ascertain the height.
The Nepali team chose the Bay of Bengal as their sea-level base to work from and figured out a ~155 mile sequence of line-of sight stations up to the point where Everest first became visible, which could be measured and added together. Nepali surveyor and mountaineer Khimlal Gautam reached the summit on May 22nd 2019 in the early hours of the morning alongside another Nepali surveyor and three Sherpa. The two hours spent working with GPS equipment and ground-penetrating radar caused Gautam to lose a toe to frostbite, the BBC reports.
The Chinese team summited this May, becoming the only team in 2020 to reach the top due to the Chinese COVID-19 foreign travel ban. This second team used China's BeiDou satellite navigation system - a rival to the Global Positioning System - and the Yellow Sea as their sea-level base.
The devastating earthquake measuring 7.8 on the moment magnitude scale in 2015 - which killed over 9,000 people in Nepal and 18 climbers in an avalanche at Everest Base Camp - is thought by some geologists to have diminished the snow pack, while the elevation of the rock has raised through plate tectonic shifts or possibly due to the earthquake, while other peaks in the Himalaya were recorded to have lost around a metre in height following the event.