There are two major climate types in the Arctic: the polar maritime climate and the polar continental climate.
Characterised by stormy and wet winters (with 60 cm-125 cm of annual precipitation) and cool and cloudy summers (with average temperatures at 10 degrees Celsius), the polar maritime climate is prevalent in coastal areas such as Alaska, Iceland, northern Russia, and Scandinavia.
Interior Arctic regions, which are dryer, with less snow in the winter and more sun in the summer, have a polar continental climate. Even so, winter weather is severe throughout the Arctic, including in the polar continental climate, with average January temperatures falling below -40 degrees Celsius in some parts of Siberia, where the lowest recorded temperatures hover at -50 degrees Celsius. In the winter, the Arctic sees limited sunlight during polar nights, when nighttime lasts for more than 24 hours at a time and the sun does not cross the horizon and it is difficult to even count the days. The several million people living above the Arctic circle experience this extreme in solar radiation annually. Humans are most active during daytime, the complete absence of which takes a toll on both the body and the mind, increasing risks of depression (due to insufficient serotonin production) and anxiety, nervousness and irritability, and drowsiness and fatigue, in addition to worsening chronic illnesses, weakening one’s immune system, slowing down hair growth and skin regeneration, and causing other dermatological problems. On the other hand, polar days (also called midnight sun) – when the sun remains above the horizon and brings 24+ hours of daylight – poses yet other challenges to humans, including trouble sleeping, hyperactivity, fatigue, and mood disturbances, amongst others.
Temperatures are so low year-round that the ground remains permanently frozen in much of the Arctic; this ground, called permafrost, covers nearly one-fourth of Earth’s surface, going as deep as 1,500 feet in parts of Alaska and Canada and even deeper in Siberia, where the deepest permafrost extends 2,000 feet. Permafrost thins from the north to the south.
In the polar continental climate, extended daylight hours in the summer melt the top layer of permafrost. Around the time of the summer solstice, the Arctic experiences another extreme of solar radiation: the sun does not set during polar days. As is the case in the polar maritime climate, summers are mild and cool with average temperatures at 10 degrees Celsius, though temperatures rise above 30 degrees in some places.
As cold air retains less water vapor than warm air, humidity is low in much of the Arctic. In certain places, the air is as dry as the air in the Sahara Desert. Humidity is highest in the summer over bodies of water and coastal areas where water evaporates, while remaining low over land areas. Humidity is lowest in the winter, when sea ice covers much of the Arctic Ocean and there is little surface water for evaporation. Areas with no sea ice continue to experience evaporation in the winter and condensing water vapor produces a fog that makes the ocean look as if it is steaming.
Precipitation is also low in much of the Arctic and some places, known as polar deserts, receive as little rain (or snow) as the Sahara Desert. The Atlantic sector – the stormy area between Greenland and Scandinavia – is an exception because of warmer air. In the winter, almost all precipitation falls as snow over land and the rest of the Arctic Ocean, though it rains on rare occasions when warm air is carried into the area. Snow also falls in the summer in the Arctic region, accounting for half of the precipitation at the North Pole during this season. Snow is rare over the Atlantic sector in the summer.