Climates in the Polar Domain, located at high latitudes, are controlled chiefly by polar and arctic air masses. In general, climates in the Polar Domain are characterized by low temperatures, severe winters, and small amounts of precipitation, most of which falls in summer. Polar systems are dominated by a periodic fluctuation of energy and temperature in which the annual range is far greater than the diurnal range. The intensity of radiation is never very high compared to systems of the middle latitudes and tropics.
In areas where summers are short and temperatures are generally low throughout the year, temperature efficiency rather than effectiveness of precipitation is the critical factor in plant distribution and soil development. Two major divisions have been recognized and delimited in terms of temperature efficiency--the tundra and the subarctic tayga.