Year-round winter refers to locations where temperatures remain consistently below the freezing point of water throughout the entire year. This condition is characterized by perpetual ice and snow cover without seasonal thawing. These environments exist because specific geographical and atmospheric factors prevent solar energy from warming the surface above 0°C (32°F). The two primary mechanisms involve either extreme latitude, which limits solar input, or extreme altitude, which causes atmospheric cooling.
Perpetual Ice Sheets: The Polar Extremes
The most expansive areas experiencing year-round winter are the vast ice sheets covering the polar extremes, specifically the interior of Antarctica and the central plateau of Greenland. Temperatures are regulated by high latitude, where the sun is always low, delivering minimal energy per unit area. During the long polar night, there is no direct solar energy to counteract the intense radiative cooling of the surface.
The massive, bright white surface of the ice sheets reinforces the cold through the ice-albedo effect. Albedo measures how much solar radiation a surface reflects; fresh snow is highly reflective, returning up to 85% of incoming sunlight back into space. This reflection prevents the surface from absorbing heat, maintaining a frozen state even during the summer months.
The interior of the East Antarctic Plateau exemplifies this extreme environment. The lowest air temperature ever recorded on Earth was measured here, dropping to -89.2°C (-128.6°F). The sheer mass and thickness of the ice sheets, which can be thousands of meters deep, create a high-altitude landmass that further intensifies the cold. The average annual temperature on the high Antarctic plateau can be as low as -56°C (-69°F).
Altitude and Atmospheric Cold: Mountain Summits
Year-round winter conditions can also be found in high-altitude mountain ranges, even those located near the equator. The primary mechanism for this cold is the atmospheric lapse rate, which describes the rate at which air temperature decreases with increasing altitude. On average, the temperature drops by about 3.5°F (1.94°C) for every 1,000 feet of elevation gained.
Peaks that rise high enough, such as the highest summits of the Himalayas or the Andes, can exceed the elevation where the average temperature remains below freezing throughout the year. Although these regions receive intense solar radiation due to the thin atmosphere, the air itself is less dense and contains fewer molecules to absorb and retain heat. The thin atmosphere acts as a poor insulator, allowing heat to escape quickly back into space.
This mechanism explains the permanent snow and ice caps found on mountains like Mount Kilimanjaro in Africa. Despite the warm air temperatures at the base of the mountain, the extreme elevation pushes the summit into a perpetual winter zone. The combination of the lapse rate and the reduced heat retention of the high-altitude air ensures that the snow and ice persist without melting.
Defining Year-Round Winter: Climate Classification
The scientific community uses the Köppen climate classification system to formally define and map these zones of permanent cold. Within this system, the “Ice Cap” climate is designated by the code EF. The EF classification is strictly defined as a climate where the mean temperature of the warmest month never rises above 0°C (32°F).
This specific temperature threshold distinguishes true year-round winter from merely very cold environments. If any month registers an average temperature above freezing, the ice and snow will begin to melt, preventing the formation of permanent ice caps. The EF classification is applied to the interior regions of Antarctica and Greenland, as well as the highest mountain peaks globally.
The EF climate is contrasted with the “Tundra” climate, designated ET, which is also a polar climate but has a slightly warmer definition. Tundra regions experience a summer season where the warmest month averages between 0°C (32°F) and 10°C (50°F). This brief warming period allows the snow to melt and supports the growth of low-lying vegetation.