Visualization of the ice and snow covering Earth's northern and southern polar regionsNorthern Hemispherepermafrost (permanently frozen ground) in purple
TheArctic has various definitions, including the region north of theArctic Circle (currently Epoch 2010 at 66°33'44" N), or just the region north of60° north latitude, or the region from the North Pole south to thetimberline.[1] TheAntarctic is usually defined simply as south of60° south latitude, or the continent of Antarctica. The 1959Antarctic Treaty uses the former definition.
The two polar regions are distinguished from the other two climatic and biometric belts of Earth, atropics belt near the equator, and twomiddle latitude regions located between the tropics andpolar regions.
Polar regions receive less intensesolar radiation than the other parts of Earth because the Sun's energy arrives at anoblique angle, spreading over a larger area, being less concentrated, and also travels a longer distance through the Earth's atmosphere in which it may be absorbed, scattered or reflected, which is the same thing that causes winters to be colder than the rest of the year except in tropical regions.
Theaxial tilt of the Earth has the mosteffect on climate of the polar regions due to its latitude. However, since the polar regions are the farthest from theequator, they receive the weakest solar radiation and are therefore generally frigid year round due to the earth's axial tilt of 23.5° not being enough to create a high maximum middaydeclination to sufficiently compensate the Sun's rays for the high latitude even in summer, except for relatively brief periods in peripheral areas near the polar circles. The large amount of ice and snow also reflects and weakens of what weak sunlight the polar regions receive further, contributing to the cold. Polar regions are characterized by extremely cold temperatures, heavyglaciation wherever there is sufficientprecipitation to form permanentice, short and still cold summers, and extreme variations in daylight hours, withtwenty-four hours of daylight in summer, andcomplete darkness atmid-winter.
There are many settlements in Earth's north polar region. Countries with claims to Arctic regions are: theUnited States (Alaska),Canada (Yukon, theNorthwest Territories andNunavut),Denmark (Greenland),Norway,Finland,Sweden,Iceland, andRussia. Arctic circumpolar populations, though small, often share more in common with each other than with other populations within their national boundaries. As such, the northern polar region is diverse in human settlements and cultures.
While there are no indigenous human cultures, there is a complex ecosystem, especially along Antarctica'scoastal zones. Coastalupwelling provides abundant nutrients that feedkrill, a type of marineCrustacea, which in turn feed a complex of living creatures frompenguins toblue whales.[citation needed]
