Climate is the average an variations of weather in a region over long periods of time. The climate of a location is affected by its latitude, terrain, persistent ice or snow cover, as well as nearby oceans and their currents. Climates can be classified using parameters such as temperature and rainfall to define specific climate types. The most commonly used classification scheme is the one originally developed by Wladimir Koeppen. The Thornthwaite system, in use since 1948, incorporates evapotranspiration in addition to temperature and precipitation information and is used in studying animal species diversity and potential impacts of climate changes. The Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses defining the climate for certain areas.