Among the peaks of Mount Carstensz, Ngga Pulu is the one summit with a genuine indigenous name. The others carry the residue of colonial naming: Carstensz from a Dutch captain who sighted glaciers near the equator in 1623 and was laughed at in Europe for claiming to have seen snow in the tropics; Sumantri from a recently-deceased Indonesian minister of mines; a confusion of Puntjak Soekarno and Puncak Jaya layered on top through political changes in the 1960s. Heinrich Harrer, the Austrian mountaineer famous for his years in Tibet, mapped the area in 1962 and called one of the summits Sunday Peak because of a religious scruple. Ngga Pulu kept its own name throughout. What it means in Amung is its own story.

On 5 December 1936, Anton Colijn, Jean Jacques Dozy, and Frits Wissel crossed the Northwall Firn and stood on the summit of Ngga Pulu. Their barometric measurements put it somewhere near 4,862 meters, though Australian surveyors in 1973 would later establish that the 1936 instruments had been running high. The corrected figure placed Ngga Pulu firmly as the highest peak on the continent of Australia-New Guinea. At the time, virtually all the key saddles connecting the Carstensz summits were buried under ice, which meant Carstensz Pyramid, the now-famous rocky spire, was considered a subsidiary of Ngga Pulu. The topography was ice. The ice decided the ranking.

After Colijn's party came a long gap. Harrer's expedition in 1962, followed by a Japanese-Indonesian team in 1964. A British climber named Dick Isherwood made the first ascent of the high north face alone in September 1972, a solo push up a wall of unstable ice and equatorial snow that climbers familiar with the Alps described afterward as something altogether different in character. The approach takes days of slog through rainforest from Timika or Sugapa. The summit day is short, cold, and technical. The descent, as climbers here say, is where the trouble lives.

The Australian scientific expeditions of 1971 to 1973 began measuring what time and warming were doing to these rare equatorial glaciers. By the year 2000, every glacier on New Guinea outside the immediate Carstensz area had vanished. Puncak Trikora, east of here, lost its icefield sometime between 1939 and 1962. Sumantri, long considered a lesser peak than Ngga Pulu, emerged from its ice cover as a bare rock summit and was measured at 4,870 meters, a handful of meters higher than the still ice-capped Ngga Pulu. The key saddle that had kept Ngga Pulu structurally dominant melted, collapsed the prominence, and demoted the mountain to a sub-peak. Puncak Jaya, the Carstensz Pyramid itself, emerged as the new king at 4,884 meters.

Scientists monitoring the retreat estimate that all remaining New Guinea glaciers may disappear somewhere between 2020 and 2030. When they do, the Carstensz area will become a geography of rock only, ending a history that runs back thousands of years to when the last ice age filled these valleys. Ngga Pulu will still sit there, still 4,862 meters of limestone uplifted from ancient seabed by the slow grinding collision of the Australian and Pacific plates. It simply will no longer carry its ice. The peak that was, for centuries, the tallest thing between two great mountain ranges half a world apart, will close that chapter of its life quietly, summit by shrinking summit, within a span of time any living person can watch.