Latitude
Latitude is the primary factor affecting arctic climate because solar radiation is not received in high latitudes during the polar night and is continuous during mid summer. In addition, solar radiation is most intense at the equator and least intense at the poles. Because the earth is nearly spherical, parallel beams of incoming solar radiation strike the surface at lower latitudes more directly than at higher latitudes. At higher latitudes, solar radiation spreads over a greater area and is less intense per unit surface area than at lower latitudes. The solar beam also has a longer path through the atmosphere in high latitudes than near the Equator. In contrast to incoming solar radiation, the amount of infrared radiation leaving the earth-atmosphere system is not a function of latitude. Latitudes higher than 30° experience a net cooling over the course of a year because outgoing longwave radiation exceeds incoming shortwave radiation. Heat is transported from the equator to the Arctic primarily by the exchange of air masses: thus the Arctic is a heat sink.
Mitigating Influence of Other Factors
Ocean currents and the distribution of land and sea keep some parts of the Arctic warmer than would be expected based purely on their latitude. For example, Svalbard (80 degrees North), being influenced by proximity to warm ocean currents, has much less persistent sea ice than the coasts of more southerly Labrador and the Kamchatka Peninsula.