Alpine climate is the average weather (climate) for a region above the tree line. The climate becomes coler at high elevations—this characteristic is described by the lapse rate of air: air will tend to get colder as it rises, since it expands. The dry adiabatic lapse rate is 10°C per km of elevation or altitude. Therefore, moving up 100 meters on a mountain is roughly equivalent to moving 80 kilometers (45 miles or 0.75° of latitude) towards the pole. This relationship is only approximate, however, since local factors such as proximity to oceans can drastically modify the climate.