Measurement

Radhanath Sikdar, an Indian mathematician and surveyor from Bengal, was the first to identify Everest as the world's highest peak in 1852, using trigonometric calculations based on measurements of "Peak XV" (as it was then known) made with theodolites from 240 km (150 miles) away as part of the Great Trigonometric Survey of India. Measurement could not be made from closer due to a lack of access to Nepal. Peak XV was found to be exactly 29,000 feet (8,839 m) high, but was publicly declared to be 29,002 feet (8,840 m). The arbitrary addition of 2 feet (0.6 m) was to avoid the impression that an exact height of 29,000 feet was nothing more than a rounded estimate.

More recently, the mountain has been found to be 8,848 m (29,028 feet) high, although there is some variation in the measurements. The mountain K2 comes in second at 8,611 m (28,251 ft) high. On May 22, 2005, the People's Republic of China's Everest Expedition Team ascended to the top of the mountain. After several months' measurement and calculation, on October 9, 2005, the PRC's State Bureau of Surveying and Mapping officially announced the height of Everest as 8,844.43 m ± 0.21 m (29,017.16 ± 0.69 ft). They claimed it was the most accurate measurement to date. This height is based on the actual highest point of rock and not on the snow and ice covering it. The Chinese team also measured a snow/ice depth of 3.5 m, which is in agreement with a net elevation of 8,848 m. The snow and ice thickness varies over time, making a definitive height of the snow cap impossible to determine.

The elevation of 8,848 m (29,029 ft) was first determined by an Indian survey in 1955, made closer to the mountain, also using theodolites. It was subsequently reaffirmed by a 1975 Chinese measurement. In both cases the snow cap, not the rock head, was measured. In May 1999 an American Everest Expedition, directed by Bradford Washburn, anchored a GPS unit into the highest bedrock. A rock head elevation of 8,850 m (29,035 ft), and a snow/ice elevation 1 m (3 ft) higher, were obtained via this device. Although it has not been officially recognized by Nepal, this figure is widely quoted. Geoid uncertainty casts doubt upon the accuracy claimed by both the 1999 and 2005 surveys.

A detailed photogrammetric map (at a scale of 1:50,000) of the Khumbu region, including the south side of Mount Everest, was made by Erwin Schneider as part of the 1955 International Himalayan Expedition, which also attempted Lhotse. An even more detailed topographic map of the Everest area was made in the late 1980s under the direction of Bradford Washburn, using extensive aerial photography.

It is thought that the plate tectonics of the area are adding to the height and moving the summit north-eastwards. Two accounts suggest the rates of change are 4 mm per year (upwards) and 3-6 mm per year (northeastwards), but another account mentions more lateral movement (27 mm), and even shrinkage has been suggested.

The Mount Everest region, and the Himalayas in general, are thought to be experiencing ice-melt due to global warming.[17] The exceptionally heavy southwest summer monsoon of 2005 is consistent with continued warming and augmented convective uplift on the Tibetan plateau to the north.