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Alpine ClimateFor the climate of the mountains named the Alps, see Climate of the Alps. Alpine climate is the average weather (climate) for a region above the tree-line. This climate is colder at high elevations, due to the lapse rate of air: air will tend to get colder as it rises, since it expands. The dry adiabatic lapse rate is 10C per km of elevation or altitude. Therefore, moving up 100 meters on a mountain is roughly equivalent to moving 80 kilometers (45' (0.75) of latitude) towards the pole http://www.unep-wcmc.org/mountains/mountain_watch/pdfs/mountainEnvironments.pdf. This relationship is only approximate, however, since local factors such as proximity to oceans can drastically modify the climate. There have been several attempts at quantifying what constitutes an alpine climate. Climatologist Wladimir Kppen demonstrated a relationship between the Arctic and Antarctic tree lines and the 10C summer isotherm; i.e., places where the average temperature in the warmest calendar month of the year is below 10C cannot support forests. See Kppen climate classification for more information. However, Otto Nordenskild theorized that winter conditions also play a role: His formula is W = 9 - 0.1 C, with W denoting the average temperature in the warmest month and C the average of the coldest month, both in degrees Celsius (this would mean, for example, that if a particular location had an average temperature of -20C in its coldest month, the warmest month would need to average 11C or higher for trees to be able to survive there). Nordenskild's line tends to run to the north of Kppen's near the west coasts of the Northern Hemisphere continents, south of it in the interior sections, and at about the same latitude along the east coasts of both Asia and North America. In the Southern Hemisphere, all of Tierra del Fuego lies outside the polar region in Nordenskild's system, but part of the island (including Ushuaia, Argentina) is reckoned as being within the Antarctic under Kppen's. In 1947, Holdridge improved on these schemes, by defining biotemperature: the mean annual temperature, where all temperatures below 0C are treated as 0C (because it makes no difference to plant life, being dormant). If the mean biotemperature is between 1.5C and 3C http://www.personal.dundee.ac.uk/~amjones/dundee/36biomes.htm, Holdridge quantifies the climate as alpine (or subpolar, of the low temperature is caused by latitude).
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