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An iceberg, which is commonly associated with cold
Signal "cold" – unofficial (except recommended by CMAS), it is nonetheless used by many schools of diving and propagated through diving websites as one of the more useful additional signals[1]
Goose bumps, a common physiological response to cold, aiming to reduce the loss of body heat in a cold environment
A photograph of the snow surface at Dome C Station, Antarctica. A part of the notoriously cold Polar Plateau, it is representative of the majority of the continent's surface.

Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00 K on the Kelvin scale, an absolute thermodynamic temperature scale. This corresponds to −273.15 °C on the Celsius scale, −459.67 °F on the Fahrenheit scale, and 0.00 °R on the Rankine scale.

Since temperature relates to the thermal energy held by an object or a sample of matter, which is the kinetic energy of the random motion of the particle constituents of matter, an object will have less thermal energy when it is colder and more when it is hotter. If it were possible to cool a system to absolute zero, all motion of the particles in a sample of matter would cease and they would be at complete rest in the classical sense. The object could be described as having zero thermal energy. Microscopically in the description of quantum mechanics, however, matter still has zero-point energy even at absolute zero, because of the uncertainty principle.

Cooling

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Main article: Refrigeration

Cooling refers to the process of becoming cold, or lowering in temperature. This could be accomplished by removing heat from a system, or exposing the system to an environment with a lower temperature.

Coolants are fluids used to cool objects, prevent freezing and prevent erosion in machines.[2]

Air cooling is the process of cooling an object by exposing it to air. This will only work if the air is at a lower temperature than the object, and the process can be enhanced by increasing the surface area, increasing the coolant flow rate, or decreasing the mass of the object.[3][better source needed]

Another common method of cooling is exposing an object to ice, dry ice, or liquid nitrogen. This works by conduction; the heat is transferred from the relatively warm object to the relatively cold coolant.[4]

Laser cooling and magnetic evaporative cooling are techniques used to reach very low temperatures.[5][6]

History

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Early history

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In ancient times, ice was not adopted for food preservation but used to cool wine which the Romans had also done. According to Pliny, Emperor Nero invented the ice bucket to chill wines instead of adding it to wine to make it cold as it would dilute it.[7]

Some time around 1700 BC Zimri-Lim, king of Mari Kingdom in northwest Iraq had created an "icehouse" called bit shurpin at a location close to his capital city on the banks of the Euphrates. In the 7th century BC the Chinese had used icehouses to preserve vegetables and fruits. During the Tang dynastic rule in China (618–907 AD) a document refers to the practice of using ice that was in vogue during the Eastern Chou Dynasty (770–256 BC) by 94 workmen employed for "Ice-Service" to freeze everything from wine to dead bodies.[7]

Shachtman says that in the 4th century AD, the brother of the Japanese emperor Nintoku gave him a gift of ice from a mountain. The Emperor was so happy with the gift that he named the first of June as the "Day of Ice" and ceremoniously gave blocks of ice to his officials.[7]

Even in ancient times, Shachtman says, in Egypt and India, night cooling by evaporation of water and heat radiation, and the ability of salts to lower the freezing temperature of water was practiced. The ancient people of Rome and Greece were aware that boiled water cooled quicker than the ordinary water; the reason for this is that with boiling of water carbon dioxide and other gases, which are deterrents to cooling, are removed; but this fact was not known till the 17th century.[7]

From the 17th century

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Shachtman says that King James VI and I supported the work of Cornelis Drebbel as a magician to perform tricks such as producing thunder, lightning, lions, birds, trembling leaves and so forth. In 1620 he gave a demonstration in Westminster Abbey to the king and his courtiers on the power of cold.[8] On a summer day, Shachtman says, Drebbel had created a chill (lowered the temperature by several degrees) in the hall of the Abbey, which made the king shiver and run out of the hall with his entourage. This was an incredible spectacle, says Shachtman. Several years before, Giambattista della Porta had demonstrated at the Abbey "ice fantasy gardens, intricate ice sculptures" and also iced drinks for banquets in Florence. The only reference to the artificial freezing created by Drebbel was by Francis Bacon. His demonstration was not taken seriously as it was considered one of his magic tricks, as there was no practical application then. Drebbel had not revealed his secrets.[9]

Shachtman says that Lord Chancellor Bacon, an advocate of experimental science, had tried in Novum Organum, published in the late 1620s, to explain the artificial freezing experiment at Westminster Abbey, though he was not present during the demonstration, as "Nitre (or rather its spirit) is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its own cold, but the salt by supplying activity to the cold snow." This explanation on the cold inducing aspects of nitre and salt was tried then by many scientists.[10]

Shachtman says it was the lack of scientific knowledge in physics and chemistry that had held back progress in the beneficial use of ice until a drastic change in religious opinions in the 17th century. The intellectual barrier was broken by Francis Bacon and Robert Boyle who followed him in this quest for knowledge of cold.[11] Boyle did extensive experimentation during the 17th century in the discipline of cold, and his research on pressure and volume was the forerunner of research in the field of cold during the 19th century. He explained his approach as "Bacon's identification of heat and cold as the right and left hands of nature".[12] Boyle also refuted some of the theories mooted by Aristotle on cold by experimenting on transmission of cold from one material to the other. He proved that water was not the only source of cold but gold, silver and crystal, which had no water content, could also change to severe cold condition.[13]

19th century

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Out In The Cold, Léon Bazille Perrault

In the United States from about 1850 till end of 19th century export of ice was second only to cotton. The first ice box was developed by Thomas Moore, a farmer from Maryland in 1810 to carry butter in an oval shaped wooden tub. The tub was provided with a metal lining in its interior and surrounded by a packing of ice. A rabbit skin was used as insulation. Moore also developed an ice box for domestic use with the container built over a space of 6 cubic feet (0.17 m3) which was filled with ice. In 1825, ice harvesting by use of a horse drawn ice cutting device was invented by Nathaniel J. Wyeth. The cut blocks of uniform size ice was a cheap method of food preservation widely practiced in the United States. Also developed in 1855 was a steam powered device to haul 600 tons of ice per hour. More innovations ensued. Devices using compressed air as a refrigerants were invented.[14]

20th century

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Iceboxes were in widespread use from the mid-19th century to the 1930s, when the refrigerator was introduced into the home. Most municipally consumed ice was harvested in winter from snow-packed areas or frozen lakes, stored in ice houses, and delivered domestically as iceboxes became more common.

In 1913, refrigerators for home use were invented. In 1923 Frigidaire introduced the first self-contained unit. The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s.[15] Home freezers as separate compartments (larger than necessary just for ice cubes) were introduced in 1940. Frozen foods, previously a luxury item, became commonplace.

Physiological effects

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Cold has numerous physiological and pathological effects on the human body, as well as on other organisms. Cold environments may promote certain psychological traits, as well as having direct effects on the ability to move. Shivering is one of the first physiological responses to cold.[16] Even at low temperatures, the cold can massively disrupt blood circulation. Extracellular water freezes and tissue is destroyed. It affects fingers, toes, nose, ears and cheeks particularly often. They discolor, swell, blister, and bleed. The so-called frostnip leads to local frostbite or even to the death of entire body parts. Only temporary cold reactions of the skin are without consequences. As blood vessels contract, they become cool and pale, with less oxygen getting into the tissue. Warmth stimulates blood circulation again and is painful but harmless. Comprehensive protection against the cold is particularly important for children and for sports. Extreme cold temperatures may lead to frostbite, sepsis, and hypothermia, which in turn may result in death.[17][18]

Common myths

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A common, but false, statement states that cold weather itself can induce the identically named common cold.[19] No scientific evidence of this has been found, although the disease, alongside influenza and others, does increase in prevalence with colder weather.

Notable cold locations and objects

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Boomerang Nebula
Neptune's moon Triton

Mythology and culture

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  • Niflheim was a realm of primordial ice and cold with nine frozen rivers in Norse Mythology.[40]
  • The "Hell in Dante's Inferno" is stated as Cocytus a frozen lake where Virgil and Dante were deposited.[41]

See also

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  • Technical, scientific
    • Chiller – Machine that removes heat from a liquid coolant
    • Cryogenics – Study of the production and behaviour of materials at very low temperatures
    • Cryosphere – Earth's surface where water is frozen
    • Freezing point – Temperature at which a solid turns liquid
    • Negative temperature – Physical systems hotter than any other
    • Coldness – Measure of the coldness of a system
    • Ultracold atom – Atoms kept at temperatures close to absolute zero
  • Entertainment, myth
    • Ice cream – Frozen dessert
    • Indrid Cold – Legendary creature
    • Snowball – Spherical object made from compacted snow
    • Snowman – Figure sculpted from snow
    • Winter sport – Sports or recreational activities which are played on snow or ices
  • Meteorological:
    • Atmospheric inversion – Deviation from the normal change of an atmospheric property with altitude
    • Cold front – Leading edge of a cooler mass of air
    • Freezing rain – Rain maintained at temperatures below freezing
    • Frost – Coating or deposit of ice
    • Hail – Form of solid precipitation
    • Sleet – Form of precipitation consisting of rain and melting snow
    • Snow – Precipitation in the form of ice crystal flakes
  • Geographical and climatological:
    • Glacier – Persistent body of ice that moves downhill under its own weight
    • Ice cap – Ice mass that covers a large area
    • Ice cap climate – Polar climate where no mean monthly temperature exceeds 0 °C (32 °F)
    • Ice sheet – Large mass of glacial ice

References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cold

View on Grokipedia
from Grokipedia
In common usage, cold is often a subjective , as well as the presence of low , especially in the atmosphere. Scientifically, cold refers to a state of lower compared to surroundings, where naturally flows from warmer to cooler bodies, as described by the second law of thermodynamics. perception of cold arises from thermoreceptors in the skin detecting temperature drops, triggering physiological responses like to conserve . This article explores cold through its fundamentals, such as definition, perception, and measurement; physical principles including and cooling processes; historical views from ancient times to modern ; biological impacts on and ; environmental phenomena like extreme lows and records; and technological applications alongside cultural symbolism. For the viral illness commonly known as the , see separate articles on respiratory infections.

Fundamentals

Definition and Perception

Cold is fundamentally defined in physics as the absence or relative reduction of , in contrast to , which represents the arising from the agitation and motion of molecules within a substance. This absence leads to lower molecular activity, resulting in decreased relative to a reference , such as the human body's core temperature around 37°C. Unlike , which flows from higher to lower states, cold itself is not an independent entity but a perceptual and thermodynamic descriptor of deficit. Human perception of cold primarily occurs through thermoreceptors in the skin, specifically cold-sensitive endings that detect drops via changes in activity, such as in the protein. These receptors activate when skin falls below the neutral baseline of approximately 33–34°C, with innocuous cool sensations emerging from even a 1°C decrease, while discomfort thresholds for most people arise below about 15°C (59°F) in ambient air, depending on exposure duration and . Psychological factors further modulate this sensation; for instance, the wind chill effect intensifies perceived cold by enhancing convective loss from the skin, tricking the into registering a lower than the reading alone suggests. The evolutionary basis for mammalian lies in adaptations that preserved body heat during environmental fluctuations, with the emerging as a key cold detector through structural of its melastatin homology regions, enabling rapid neural signaling for thermoregulatory behaviors like or seeking . This sensitivity likely originated in early mammals as a mechanism against nocturnal or glacial cooling events, distinguishing endothermic mammals from ectothermic ancestors by prioritizing and avoidance of .

Measurement and Scales

The measurement of cold has evolved from rudimentary devices to precise instruments, beginning with the invention of the by in 1593. This early apparatus, consisting of a glass bulb connected to a tube submerged in water, demonstrated by showing the rise and fall of liquid levels with changes, though it lacked a numerical scale. Subsequent advancements included the development of sealed liquid-in-glass s in the early , which improved accuracy by preventing influences. A significant milestone occurred in 1714 when introduced the mercury , utilizing mercury's high and low freezing point for more reliable and sensitive readings compared to alcohol-based devices. Temperature scales provide standardized frameworks for quantifying cold and heat. The Celsius scale, proposed by Anders Celsius in 1742, originally set the boiling point of water at 0° and the freezing point at 100°, but was inverted shortly after by Carolus Linnaeus to align freezing at 0°C and boiling at 100°C under standard atmospheric pressure, facilitating everyday and scientific use. The Fahrenheit scale, developed by Fahrenheit around 1724 to calibrate his mercury thermometers, defines water's freezing point at 32°F and boiling point at 212°F, chosen based on reproducible references like the freezing of brine (0°F) and human body temperature (96°F initially). For absolute measurements avoiding negative values, the Kelvin scale, introduced by William Thomson (Lord Kelvin) in 1848, sets absolute zero—the theoretical lowest temperature where molecular motion ceases—at 0 K, with water freezing at 273.15 K and boiling at 373.15 K; it uses the same degree size as Celsius but shifts the zero point by adding 273.15 to Celsius values. Conversions between these scales are essential for cross-referencing data. The scale spans 180 degrees from water's freezing to , while spans 100 degrees, yielding a ratio of 9/5 (or 1.8) degrees Fahrenheit per degree Celsius. To derive the conversion from Celsius to Fahrenheit, start with the known fixed points: 0°C corresponds to 32°F, and 100°C to 212°F. The linear relationship is thus F=(95C)+32F = \left( \frac{9}{5} C \right) + 32, where the slope 95\frac{9}{5} accounts for the degree size difference, and the +32 offsets the freezing point discrepancy. For example, 20°C converts to (95×20)+32=68°F\left( \frac{9}{5} \times 20 \right) + 32 = 68°F, and -10°C to (95×−10)+32=14°F\left( \frac{9}{5} \times -10 \right) + 32 = 14°F. The inverse, from Fahrenheit to Celsius, is C=59(F−32)C = \frac{5}{9} (F - 32). conversions are simpler: K=C+273.15K = C + 273.15. Specialized scales emerged for particular applications. The , devised by in 1730, set water's freezing at 0°R and boiling at 80°R, using alcohol in glass thermometers; it gained popularity in for meteorological and industrial purposes but declined with the rise of . Similarly, the , proposed by William Rankine in 1859, is an absolute counterpart to , with at 0°R, water freezing at 491.67°R, and boiling at 671.67°R; it finds niche use in Anglo-American contexts requiring Fahrenheit-like increments without negatives. Contemporary measurement devices extend precision across temperature ranges, including extreme cold. Digital sensors, such as thermistors and resistance temperature detectors (RTDs), convert changes into electrical signals for high-accuracy readings in and industrial settings, often with resolutions below 0.1°C. thermometers detect to measure surface temperatures non-invasively, useful for cold objects without contact, achieving accuracies of ±1°C or better in clinical and . For cryogenic applications near , specialized sensors like superconducting quantum interference devices (SQUIDs) and thermometers using or isotopes enable measurements down to millikelvin levels, calibrated on the International Temperature Scale of 1990 (ITS-90) extended to low temperatures.

Physics and Thermodynamics

Principles of Heat and Cold

The establishes the concept of as a measurable property of systems in , stating that if two systems are each in with a third system, then they are in with each other. This law provides the foundational basis for defining scales and distinguishing states of relative coldness or hotness through equilibrium conditions. The First Law of Thermodynamics, which expresses the , applies to cooling processes by stating that the change in of a equals the added to the minus the work done by the : ΔU=Q−W\Delta U = Q - W. In cooling scenarios, where QQ is removed (negative QQ), the decreases if no work is performed, leading to lower temperatures without violating . This principle underscores that cold states result from energy transfer out of the rather than energy destruction. The Second Law of Thermodynamics governs the directionality of cooling, asserting that spontaneous occurs from higher to lower temperatures, resulting in an increase in the total of the . For a reversible , the change is given by dS=dQrevTdS = \frac{dQ_{\text{rev}}}{T}, but in irreversible cooling, the ensures ΔSuniverse>0\Delta S_{\text{universe}} > 0. Thus, natural cooling , such as flowing into a colder , are driven by the tendency toward greater disorder and are irreversible without external work. The Third Law of Thermodynamics defines , at 0 K or -273.15 °C, as the theoretical lower limit of where the of a perfect reaches a minimum (often zero), and states that this state is unattainable by any finite process. This unattainability arises because approaching would require infinite steps to remove residual , as changes diminish proportionally with . Cold states emerge from heat loss through three primary mechanisms: conduction, , and . Conduction involves the transfer of through direct molecular collisions within a or stationary , governed by Fourier's : [q](/page/Q)=−[k](/page/K)∇T\mathbf{[q](/page/Q)} = -[k](/page/K) \nabla T, where [q](/page/Q)\mathbf{[q](/page/Q)} is the vector, kk is the conductivity, and ∇T\nabla T is the . This mode leads to cooling when a warmer region contacts a cooler one, with heat flowing down the gradient until equilibrium. Convection occurs via the bulk motion of a fluid, carrying thermal energy away from a surface, and is described by Newton's law of cooling: q=h(Ts−T∞)q = h (T_s - T_\infty), where qq is the heat transfer rate per unit area, hh is the convective heat transfer coefficient, TsT_s is the surface temperature, and T∞T_\infty is the fluid temperature far from the surface. In natural convection, density differences driven by temperature induce fluid movement, enhancing cooling; forced convection amplifies this through external flow. Radiation transfers electromagnetically without a medium, with net exchange between surfaces following the Stefan-Boltzmann law: q=ϵσ(T4−Tsurr4)q = \epsilon \sigma (T^4 - T_{\text{surr}}^4), where ϵ\epsilon is the , σ\sigma is the Stefan-Boltzmann constant (5.67×10−85.67 \times 10^{-8} W/m²K⁴), TT is the absolute of the emitting body, and TsurrT_{\text{surr}} is the surroundings' . All bodies emit proportional to the of their , enabling cooling even in , as cooler surroundings absorb more than they emit at lower TT.

Cooling Processes

Cooling processes encompass the physical mechanisms through which is removed from objects or environments, leading to lower temperatures without external intervention. These processes rely on fundamental thermodynamic principles, such as via phase transitions, expansion, and , and are observable in both microscopic and large-scale natural systems. Evaporative cooling occurs when a changes to vapor, absorbing from the surroundings to provide the of . This process is quantified by Q=mLvQ = m L_v, where [Q](/page/Q)[Q](/page/Q) is the heat absorbed, mm is the mass of the evaporating , and LvL_v is the of , approximately 2260 kJ/kg for at standard conditions. In biological contexts, such as human sweat , on the skin absorbs body heat during , reducing surface temperature even in environments warmer than the body, thereby aiding . Adiabatic cooling arises from the expansion of gases without exchange with the surroundings, converting into work and lowering . In atmospheric systems, rising air parcels expand due to decreasing , cooling at the dry adiabatic of about 9.8°C per kilometer. This mechanism drives cloud formation and precipitation in convective storms. The related Joule-Thomson effect, observed in real gases expanding through a , also produces cooling for most gases at , as decreases with pressure drop. Radiative cooling predominates at night when surfaces emit to the cold sky, resulting in net heat loss. Objects approximate blackbody radiators, following the Stefan-Boltzmann law, where the power radiated is P=σAT4P = \sigma A T^4, with σ\sigma as the Stefan-Boltzmann constant (5.67 × 10^{-8} W/m²K⁴), AA the surface area, and TT the absolute temperature in . The net heat loss is the difference between emitted and absorbed radiation, often cooling Earth's surface by several degrees under clear skies, as the atmosphere is relatively transparent to longwave infrared. Phase changes contribute to cooling by absorbing large amounts of without temperature variation. During freezing, liquid releases heat upon forming , but the reverse——absorbs 334 kJ/kg, stabilizing temperatures; however, in cooling contexts, sublimation of solids like (solid CO₂) directly to gas absorbs 571 kJ/kg, enabling rapid temperature drops to -78.5°C. 's high , about 4.184 J/g·°C, further delays cooling in aqueous systems by requiring substantial energy removal to lower temperature, moderating environmental fluctuations. In natural settings, such as polar nights, extended darkness prevents solar heating, allowing unchecked radiative cooling to drive extreme temperatures. At the South Pole, surface air temperatures plummet to around -60°C during winter months due to this radiative imbalance, with minimal atmospheric mixing exacerbating the chill.

Historical Development

Ancient and Medieval Views

In ancient Greek philosophy, cold was conceptualized as one of the four primary qualities—alongside hot, wet, and dry—that defined the fundamental elements of matter. Aristotle, in his treatise On Generation and Corruption, described earth as the element characterized by the qualities of cold and dry, contrasting it with fire (hot and dry), air (hot and moist), and water (cold and moist); these qualities were seen as active principles enabling natural change and mixture. This elemental theory influenced subsequent understandings of cold as an intrinsic property essential to the composition and transformation of substances. Hippocrates extended these ideas into through humoral theory, positing that the body contained four humors—blood, , yellow , and black —each associated with specific qualities and elements. , linked to and characterized as cold and moist, was believed to predominate in winter and contribute to imbalances such as or when in excess, disrupting the body's equilibrium of qualities. Imbalances involving cold humors were thus viewed as causes of disease, treatable by restoring qualitative harmony through diet, environment, or purges. In Chinese philosophical traditions, particularly Taoism, cold was embodied in the concept of yin, one of two complementary forces (yin and yang) that underpin the cosmos and natural processes. As articulated in ancient texts like the I Ching and Huangdi Neijing, yin represented the passive, contractive, dark, and cold principle, opposing the active, expansive, hot, and light yang; balance between them was essential for health and harmony. This duality framed cold not as an isolated phenomenon but as a vital, interdependent force in cycles of change. Similarly, ancient Indian medicine in Ayurveda identified cold as a key quality within the three doshas—vata, pitta, and kapha—that govern physiological functions, derived from the five elements (ether, air, fire, water, earth). Vata dosha, composed of ether and air, was cold and dry, promoting movement but potentially causing disorders like anxiety or dryness when imbalanced; kapha dosha, from water and earth, was cold, moist, and heavy, providing stability but leading to congestion or lethargy in excess. These cold qualities were managed through warming foods, herbs, and lifestyles to maintain doshic equilibrium, as detailed in foundational texts like the Charaka Samhita. During the medieval period in , alchemical thought integrated Aristotelian qualities with Islamic influences, treating cold as a manipulable property in the transmutation of substances. Influenced by figures like (Ibn Sina), who in works such as the Canon of Medicine distinguished sensible qualities—like the perceptible coldness of a substance—from its essential nature, alchemists viewed cold as a tool for and fixation in processes aiming to refine base metals into nobler forms. Avicenna's framework emphasized that while sensible cold could be altered through mixture or operation, true transmutation required aligning with an object's essential qualities, shaping medieval debates on alchemy's feasibility. Early empirical observations of cold phenomena were recorded by Roman naturalist in his (77 CE), where he documented frost, , and as congelations of vapor or influenced by atmospheric conditions. Pliny noted the practical use of and for preservation, such as packing fruits in to extend their freshness by slowing decay, highlighting cold's role in inhibiting natural . These accounts blended wonder at cold's transformative effects with utilitarian insights, bridging philosophical speculation and everyday application.

Modern Scientific Advances

The transition to empirical in the study of cold began in the with experimental investigations into low temperatures and . Robert Boyle's work with air pumps in the 1660s demonstrated vacuum cooling through the expansion of air, where reducing pressure caused a noticeable drop in , laying groundwork for understanding adiabatic processes. In 1701, formulated his law of cooling, stating that the rate of temperature change of a body is proportional to the difference between its TT and the ambient TaT_a, expressed as dTdt=−k(T−Ta)\frac{dT}{dt} = -k (T - T_a), where kk is a positive constant; this empirical relation, derived from observations of hot objects cooling in air, provided a quantitative basis for convective heat loss. The advanced theoretical frameworks for cold through , emphasizing reversible cycles and absolute scales. Sadi Carnot's 1824 publication, Réflexions sur la puissance motrice du feu, introduced the cycle, which operates between a hot reservoir and a cold sink to maximize efficiency, establishing foundational principles for by showing that work extraction requires a and that perfect reversibility yields the theoretical limit. In 1848, William Thomson (later ) proposed an absolute temperature scale in his paper "On an Absolute Thermometric Scale founded on Carnot's Theory of the Motive Power of Heat," defining zero as the unattainable lower limit where molecular motion ceases, with the scale interval matching the degree but shifted by 273.15, enabling precise comparisons across thermodynamic processes. Twentieth-century breakthroughs extended experimental access to extreme cold, revealing novel material properties. In 1898, achieved the of using a continuous-flow apparatus with precoooling and insulation, producing about 20 cubic centimeters of at 20 K, which facilitated studies of gases near . In 1911, discovered while measuring mercury's electrical resistance at temperatures around 4.2 K, observing a sudden drop to zero resistance below 4.15 K, a phenomenon attributed to quantum pairing of electrons and opening avenues for low-temperature physics. Post-2000 developments have pushed quantum cooling techniques to unprecedented precision, enabling the manipulation of atomic ensembles at microkelvin scales. The first realization of Bose-Einstein condensates (BECs) in 1995 by Eric Cornell and using evaporative cooling of rubidium-87 atoms to 170 nK marked a milestone, earning the 2001 for creating this fifth where bosons occupy the en masse, exhibiting macroscopic quantum coherence. Subsequent advances in quantum cooling, such as resolved-sideband and sympathetic cooling in hybrid traps, have achieved sub-millikelvin temperatures for diverse systems including ions and mechanical oscillators, enhancing applications in quantum simulation and information processing.

Biological and Physiological Impacts

Effects on Human Physiology

Exposure to cold triggers immediate thermoregulatory responses in the to preserve core , which is normally maintained at approximately 37°C. Peripheral reduces blood flow to the skin and extremities, minimizing convective and radiative loss from the body's surface. Concurrently, activates skeletal muscles to generate through rapid contractions, increasing metabolic rate by up to fivefold in mild cold conditions. These mechanisms collectively aim to prevent a drop in core , though their effectiveness diminishes with prolonged or severe exposure. When these responses fail, hypothermia ensues, defined as a core body temperature below 35°C. In mild hypothermia (32–35°C), symptoms include intense , confusion, and impaired coordination as the body prioritizes vital organ . Moderate hypothermia (28–32°C) is marked by the cessation of , profound , and dilated pupils, reflecting metabolic slowdown and reduced cerebral function. Severe hypothermia (<28°C) poses acute risks such as ventricular arrhythmias and due to slowed electrical conduction in the heart. At the cellular level, cold exposure impairs metabolic processes by reducing enzyme activity through slowed molecular kinetics and altered protein conformations. In sub-zero conditions, formation within tissues exacerbates damage, piercing cell membranes and causing osmotic imbalances that lead to . Prolonged cold exposure can result in localized injuries like , where freezing temperatures cause formation in extracellular fluids, dehydrating cells and leading to vascular stasis and tissue from occluded blood vessels. , or , arises from extended damp exposure above freezing (typically 0–10°C), inducing , nerve damage, and eventual tissue breakdown without formation. The perceived severity of cold is amplified by , quantified by the wind chill index, which estimates on exposed using the : WC=35.74+0.6215T−35.75(V0.16)+0.4275T(V0.16)\text{WC} = 35.74 + 0.6215T - 35.75(V^{0.16}) + 0.4275T(V^{0.16}) where TT is air in °F and VV is in mph. This metric highlights how accelerates loss, equivalent to a lower still-air .

Cold Stress and

Cold refers to the physiological strain imposed by prolonged exposure to low temperatures, prompting adaptive responses in organisms to maintain . In humans, to chronic cold involves physiological adjustments such as elevated basal metabolic rates (BMR) and enhanced non-shivering thermogenesis (NST) through (BAT) activation. Populations like the , inhabiting environments, demonstrate these adaptations, with BMRs 3–19% higher than those in temperate regions, enabling efficient heat production and fat metabolism under caloric constraints. This metabolic efficiency is supported by increased BAT activity, which generates heat via uncoupled mitochondrial respiration, reducing reliance on and conserving during extended cold exposure. Genetic adaptations further enhance cold tolerance in specific populations. In Tibetans, variants in the EPAS1 gene, inherited partly from ancestry, regulate hypoxia-inducible factors to optimize oxygen use at high altitudes, indirectly aiding resilience to the combined stresses of hypoxia and cold by blunting excessive and improving vascular responses. Similarly, among , a selective sweep in the CPT1A gene (p.P479L variant) facilitates oxidation in low-carbohydrate, high-fat diets typical of subsistence, supporting sustained energy production and in extreme cold. These genetic changes highlight evolutionary pressures shaping human physiology for chronic environmental stressors. Animals exhibit diverse cold adaptation strategies, often more specialized than mechanisms. In bears, involves periodic states where core body temperature drops to approximately 30–34°C, dramatically lowering metabolic rate to 25% of basal levels while minimizing and immune suppression. This controlled allows energy conservation over months without food. , such as notothenioids, produce proteins (AFPs) that bind to nascent crystals in bodily fluids, inhibiting growth and recrystallization to prevent lethal freezing despite seawater temperatures near -1.9°C. These proteins lower the freezing point without significantly altering the melting point, creating a thermal hysteresis that protects cellular . Human interventions like leverage controlled cold exposure to mimic and enhance adaptive responses. Whole-body (WBC), typically involving exposure to -110°C for 2–3 minutes, activates BAT, reduces pro-inflammatory cytokines (e.g., IL-6, TNF-α), and alleviates muscle soreness by constricting blood vessels and limiting . Studies show WBC decreases markers post-exercise, promoting recovery and potentially improving metabolic health, though benefits vary by protocol and individual fitness. Regular sessions may induce acclimatization-like effects, boosting antioxidant defenses and vascular function. Despite these adaptations, limits exist where cold exposure triggers maladaptations. Cold-induced , or exercise-induced bronchoconstriction in cold air, narrows airways due to of dry, cold air, exacerbating symptoms like wheezing and reduced function in susceptible individuals. Raynaud's syndrome represents another vulnerability, characterized by episodic vasospasm in extremities upon cold exposure, leading to ischemia, pain, and tissue damage from impaired blood flow. These conditions underscore that while adaptations mitigate cold stress, genetic predispositions or insufficient can result in pathological responses, particularly in non-native populations.

Environmental and Extreme Cold

Natural Cold Phenomena

Natural cold phenomena encompass large-scale atmospheric, geological, and extraterrestrial processes that generate and sustain extreme low temperatures across planetary environments. These events shape global climate patterns, influence ecosystems, and reveal the dynamic interplay between Earth's systems and those of other celestial bodies. Polar vortices are large-scale, low-pressure systems of cold air encircling the Earth's polar regions, primarily in the during winter. A (SSW) event can disrupt this vortex by causing rapid temperature increases in the , often due to planetary waves propagating upward and weakening the westerly winds. This disruption distorts the polar , making it wavy and allowing frigid to plunge southward, resulting in prolonged cold snaps over mid-latitudes. Glaciers form through the accumulation and compaction of snowfall in regions where winter exceeds summer melt, compressing snow into dense over time that flows under its own weight. On a broader scale, ice ages represent extended periods of glacial expansion driven by —variations in Earth's , , and that alter the distribution and intensity of solar radiation reaching the planet. These cycles paced the Pleistocene ice ages, with the most recent concluding approximately 11,700 years ago, marking the onset of the warmer epoch. Beyond , cryovolcanism exemplifies cold phenomena on icy moons, where volatile materials like erupt instead of molten rock. On Saturn's moon , cryovolcanoes at the expel plumes of and particles through fractures known as "tiger stripes," driven by from Saturn's gravitational pull on the moon's subsurface ocean. These plumes, reaching hundreds of kilometers in height, indicate active geological processes in an otherwise frozen environment. Ocean currents play a crucial role in distributing cold water globally via the , a density-driven system often called the "global conveyor belt." Cold, dense (AABW) forms near the continent through brine rejection during formation, sinking to the ocean floor and spreading northward into the Atlantic, Indian, and Pacific basins at near-freezing temperatures around 0°C. This circulation regulates deep-ocean temperatures and influences surface patterns. Recent manifestations of these phenomena underscore their societal impacts; for instance, the February 2021 Texas cold wave, triggered by a disrupted , brought unprecedented freezing s to the region, causing widespread power grid failures, disruptions, and estimated economic losses of $80–130 billion due to inadequate infrastructure resilience.

Record Low Temperatures

The lowest air ever recorded at Earth's surface is −89.2 °C (−128.6 °F), measured at in on 21 July 1983 by Soviet researchers using standard meteorological instruments during a polar winter expedition. This record, verified by the (WMO), highlights the extreme conditions in the interior, where clear skies and high contribute to , posing significant logistical challenges for scientific stations and underscoring the limits of human habitation in such environments. In polar regions, the coldest inhabited location is in , , where temperatures reached −67.7 °C (−89.9 °F) on 6 February 1933, as documented by local weather stations. This measurement, also recognized by the WMO and , reflects the harsh of the , where small communities endure sub-zero averages throughout winter, relying on traditional adaptations like insulated dwellings and reindeer herding for survival. The record illustrates the boundary between uninhabitable extremes and human resilience in remote settlements. In laboratory settings, the lowest temperature achieved is 38 picokelvin (pK), equivalent to 38 trillionths of a degree above , attained in 2021 by physicists at the using a quantum gas in a magnetic trap during a free-fall experiment. This milestone, published in and certified by , enables studies of quantum phenomena like and Bose-Einstein condensates, advancing fields such as and precision measurement by simulating conditions near the fundamental limit of . No lower temperatures have been verified as of 2025. The coldest known natural object in the universe is the , a approximately 5,000 light-years away, with a temperature of 1 (−272.15 °C or −457.87 °F), measured via observations in the 1990s and confirmed by the Atacama Large Millimeter/submillimeter Array (ALMA) in 2013. This temperature, colder than the , results from rapid gas expansion around a dying central star, providing insights into and the of interstellar media; it remains the benchmark for natural cosmic cold as of 2025, with no verified colder objects identified.

Technological and Cultural Aspects

Cooling Technologies

represents the cornerstone of modern cooling technologies, enabling the artificial production of cold through a closed . The system comprises four primary components: a , which pressurizes and circulates the vapor; a condenser, where high-pressure vapor releases to the surroundings and condenses into liquid; an expansion valve, which reduces pressure and temperature of the liquid ; and an , where the low-pressure absorbs from the cooled space, evaporating back into vapor. The efficiency of this cycle is quantified by the (COP), defined as the ratio of cooling effect provided (QcQ_c) to the work input (WW) to the : COP=QcW\text{COP} = \frac{Q_c}{W} This metric typically ranges from 2 to 4 for practical systems, indicating that the cooling output exceeds the electrical input by a factor of 2 to 4. The historical development of , a key application of vapor-compression, began with Willis Carrier's invention in 1902 of the first modern electrical system designed to control humidity and temperature in a printing plant in , New York. This centrifugal compressor-based unit marked the shift from rudimentary ice-based cooling to engineered climate control, fundamentally transforming indoor environments in commercial and residential settings. By 2025, (HVAC) systems, predominantly reliant on vapor-compression, account for approximately 10% of global electricity consumption, underscoring their widespread adoption and energy demands amid rising temperatures and . Cryogenics extends cooling technologies to ultra-low temperatures below 120 K, with production serving as a foundational process achieved through the Linde method, which exploits the Joule-Thomson effect to cool and condense nitrogen gas to its of 77 K at . This cryogenic fluid is integral to applications, such as the initial cooldown of superconducting magnets in (MRI) scanners, where precools the system from room temperature to 77 K before achieves the final 4 K state required for . Advanced cooling innovations include thermoelectric Peltier coolers, which operate on the Peltier effect wherein an passed through a junction of two dissimilar semiconductors generates a temperature difference, absorbing heat on one side and rejecting it on the other without moving parts or refrigerants. These solid-state devices are compact and reliable for precise applications like electronics cooling. Complementing this, techniques, recognized by the 1997 awarded to , , and William D. Phillips, use tuned laser light to slow atomic motion via photon momentum transfer, achieving millikelvin temperatures for trapping neutral atoms in optical lattices or magnetic traps essential for quantum research. Sustainability efforts in cooling technologies have intensified following the 1987 , an international treaty that phased out ozone-depleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in refrigerants, prompting the adoption of low (GWP) alternatives such as hydrofluoroolefins (HFOs) with GWPs under 1 compared to thousands for legacy fluids. In architecture, passive cooling strategies enhance efficiency by minimizing mechanical reliance, exemplified by windcatchers in traditional Middle Eastern designs that channel breezes for natural ventilation and evaporative cooling, or modern implementations like cross-ventilation in the Himurja Office Building in , which uses stack effects and shaded facades to reduce indoor temperatures without energy input.

Cold in Culture and Symbolism

In , the Jötnar, a race of giants often associated with frost and inhabiting the icy realm of , embody the primordial chaos and harsh forces of nature that challenge the order of the gods. These beings, sometimes specifically termed frost giants in cultural interpretations, symbolize the untamed cold of winter and the elemental struggles central to cosmic narratives. Similarly, in , serves as the deity of the , personifying the biting chill of winter storms and the relentless freeze that sweeps across landscapes. As one of the wind gods, Boreas's winged form and association with abduction myths underscore cold's dual role as both a natural phenomenon and a for forceful isolation. Literature and art have long harnessed cold's evocative power to explore human emotion and the sublime. William Shakespeare's Richard III (1593) begins with the famous line, "Now is the winter of our discontent," where the protagonist Richard uses the metaphor of a bleak, frozen season to convey personal bitterness and political turmoil amid England's Wars of the Roses. This imagery transforms literal cold into a symbol of emotional desolation and impending upheaval. In visual art, Caspar David Friedrich's Romantic painting The Sea of Ice (1824), an oil on canvas depicting a shipwreck entombed in Arctic ice floes, captures the majestic yet terrifying indifference of frozen wilderness, evoking themes of human fragility against nature's icy dominance. Housed in Hamburg's Kunsthalle, the work reflects early 19th-century fascination with polar exploration and the Romantic ideal of cold as a profound, isolating force. Cold permeates cultural symbolism as a marker of emotional distance, purity, and transience. The idiom "cold shoulder," first recorded in Sir Walter Scott's The Antiquary (1816), denotes deliberate indifference or rejection, drawing from the image of offering a guest an uninviting cold cut of meat to signal their unwelcome status. This expression highlights cold's connotation of and disdain in everyday . In religious contexts, Buddhist traditions employ mandalas—geometric diagrams representing the —as symbols of mental purity and enlightenment, with sand mandalas ritually created and destroyed to emphasize impermanence, as the process mirrors the fleeting nature of existence. Such representations underscore cold's role in evoking clarity and detachment from worldly attachments. In modern culture, cold serves as a potent metaphor for ideological standoffs and personal introspection. The term "," popularized by U.S. statesman in a 1947 speech and referring to the period of U.S.-Soviet tensions from 1947 to 1991, evokes a state of frozen hostility without direct military engagement, marked by proxy conflicts and nuclear deterrence. This geopolitical imagery extended cold's symbolism to global alienation and restrained aggression. In contemporary media, Disney's animated film Frozen (2013) portrays Elsa's cryokinetic powers as an allegory for emotional repression and isolation, where her icy abilities stem from fear, ultimately thawed by familial love to represent and vulnerability. Festivals worldwide counter cold's gloom through communal warmth and ritual. The in , —held annually on the last Tuesday of —features a torch procession of over 1,000 "guizers" in Viking garb, culminating in the burning of a replica to symbolically banish winter's darkness and herald longer days. Rooted in 19th-century Norse revival, this event transforms the midwinter chill into a celebration of heritage and resilience against the season's harshness.

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