Cold
Overview
Cold refers to the physical and physiological state that occurs when the temperature of the surrounding environment falls below the range in which the human body feels comfortable. It is not merely a matter of low air temperature; it is a subjective and objective phenomenon determined by the complex interaction of wind, humidity, radiant heat, and an individual's ability to regulate body temperature. In meteorology, it is quantified through cold waves and apparent temperature; in medicine, it is treated as a cause of health risks such as hypothermia and frostbite; and in industry, it is treated as a resource for refrigeration, cold chains, data center cooling, and other applications.
Main content
Meteorological and climatological definitions
Cold is closely tied to atmospheric circulation. Major variables in mid-latitude cold waves include the influence of the Mongolian-Siberian air mass in winter, when the Siberian High expands and cold continental air moves southward; the inflow of cold air caused by meandering of the jet stream; and changes in the Arctic Oscillation (AO) and Arctic sea ice extent. The Korea Meteorological Administration (기상청) uses criteria such as a daily minimum temperature dropping by more than 10°C from the previous day or a minimum temperature falling below -12°C as the basis for cold-wave advisories and warnings, and issues public action guidelines.
Apparent temperature and cold-wave indices
Apparent temperature is calculated by combining air temperature with wind speed and humidity. In winter, as wind speed increases, convective heat loss from the skin surface increases, making it feel much colder than the actual air temperature; the Wind Chill Index, which reflects this, is widely used. As a concept contrasted with the summer Wet Bulb Globe Temperature (WBGT), it serves as the basis for cold-wave response policies and safety standards for outdoor workers.
Human physiology and health effects
The human body maintains a core temperature of around 37°C through cutaneous vasoconstriction, shivering (heat production via muscle contraction), and non-shivering thermogenesis via brown adipose tissue, centered on the thermoregulatory center in the hypothalamus. Prolonged exposure to cold can cause hypothermia, in which core body temperature falls below 35°C; frostbite, in which peripheral tissues freeze; and an increased risk of acute myocardial infarction and stroke due to greater cardiovascular strain. Older adults, infants and young children, people with chronic diseases, homeless people, and outdoor workers are classified as particularly vulnerable groups. The problem of 'energy poverty,' combined with inadequate indoor heating and the burden of fuel costs, is also a major cause of health disparities in winter.
Physics background
Thermodynamically, cold is the result of the direction of heat energy transfer between a system and its surroundings—that is, a spontaneous process toward thermal equilibrium. Absolute zero (0 K, about -273.15°C) is the theoretical lower limit at which the thermal motion of particles is minimized; in actual experiments, laser cooling and magnetic cooling reach the nanokelvin level. Ultracold physical phenomena such as superconductivity, superfluidity, and Bose-Einstein condensates redefine cold not as an 'inconvenience to be removed' but as a core tool for precision measurement and quantum technology.
Everyday life, culture, and industry
Clothing is designed around three axes: insulation using air layers, sweat release, and windproofing, and functional materials and electrically heated clothing have become widespread. In industry, refrigerated and frozen logistics (cold chains) are the foundation for the distribution of vaccines, pharmaceuticals, and fresh food, while liquid immersion cooling and free cooling in data centers are factors that determine power efficiency. Culturally, winter festivals, hot springs and jjimjilbangs (찜질방), heating culture, and traditions of kimjang (김장) and preserved foods have become established as modes of adaptation to cold.
Latest trends
In 2024-2025, 'polarized seasons' caused by climate change became more pronounced. While the intensity and frequency of summer heat waves increase, observations show a pattern in which rapid cold waves in winter arrive in short, intense bursts due to greater jet stream variability and Arctic warming. Accordingly, meteorological agencies in various countries are subdividing apparent-temperature-based early warnings and expanding city-level mapping of cold-wave-vulnerable populations and the operation of shelters. In industry, the expansion of heat pump adoption, efficiency improvements in district heating, and thermal energy storage (heat storage) technologies have emerged as key means of responding to surging heating demand, and cold chains, linked to the expansion of vaccine and biopharmaceutical distribution, continue to see investment in ultra-low-temperature frozen logistics infrastructure. Meanwhile, as the power and cooling demands of AI data centers surge, 'cooling technology' such as liquid immersion cooling and waste heat recycling has become a major agenda item in both science and industry, and polar research and permafrost observation are attracting attention as examples showing that cold is an indicator of changes in the Earth system.
Related topics
- [[한파]] (Cold wave)
- [[체감온도]] (Apparent temperature)
- [[저체온증]] (Hypothermia)
- [[기후변화]] (Climate change)
- [[콜드체인]] (Cold chain)