To run the calculations, scientists must give the computers thorough climate histories of different geographical regions, including natural climate changes. Mountain glacier systems are highly responsive to even subtle changes of climate, and mountain glacier systems in maritime settings, like Mount Olympus, are perhaps most sensitive and provide the most complete record of climatic change. Fortunately for scientists who study these systems, glaciers leave a permanent mark on the ground they cover. Mountain glaciers, like the ones that once draped Mount Olympus, originate at high elevations in pre-existing stream valleys that are sheltered from sunlight. Glaciers form basin-like depressions in the ground, called cirques, erosional features that remain after the ice and snow have melted.
Cirques tend to form at the level of the regional snowline, or the lower limit of perennial snow.
Over the years, cirques lose some of their definition, which helps scientists group them according to age. Studies of Mount Olympus confirm that the mountain is rising at a rate of about 0.12 to 0.14 of an inch a year. While exploring Mount Olympus, Smith and the other researchers found evidence of three different ages of cirques formed during three separate glacial periods. To determine the extent of glaciation and the average temperature during these periods, scientists measure the shape, size, and elevation of the cirques. This also paints a picture of the regional snowline and helps researchers measure the position of the 0 degree isotherm - the elevation at which water freezes.