Cold wave

A cold wave is a weather phenomenon defined by a sudden and significant cooling of the air. In various regions, people may refer to these events as a cold snap, a cold spell, an Arctic blast, or an Arctic snap. The U.S. National Weather Service uses a specific definition for this event. They look for a rapid fall in temperature that occurs within a 24-hour period. This temperature drop must be large enough to require substantial protection for industry, commerce, agriculture, and social activities. The exact criteria for a cold wave depend on the rate of the temperature fall and the minimum temperature reached. This minimum temperature changes based on the specific geographical region and the time of year. If a cold wave is large enough in magnitude and lasts for a long time, it may be classified as a cold air outbreak (CAO).

These weather events trigger complex cause-and-effect chains across the natural and built environments. Because exposure to extreme cold requires more caloric intake, all animals and humans must consume more food to maintain body heat. If a cold wave brings heavy and persistent snow, grazing animals may be unable to reach the food they need. This can lead to death from starvation or hypothermia. In these cases, farmers often face considerable costs to purchase extra food for their livestock. Cold spells are also linked to increased mortality rates in populations globally. While both heat waves and cold waves cause deaths, more temperature-attributable deaths occur during cold waves. However, the mortality rate is higher in undeveloped regions of the world.

Cold waves can also cause significant damage to human infrastructure and technology. Extreme winter cold often causes poorly insulated water pipelines and mains to freeze. Even indoor plumbing can rupture because water expands as it freezes. This leads to property damage and expensive insurance claims. The demand for electrical power and fuels rises dramatically during these periods. However, the generation of hydroelectricity may fail if the water needed for power freezes. Some metals may also become brittle at these low temperatures. Transportation systems can fail if motor oil gels or if antifreeze fails in motor vehicles. Furthermore, fires can become a greater hazard. While snow can stop the spread of wildfires, the air during a cold wave is typically denser. This means the air contains more oxygen. When a fire draws in this unusually cold, oxygen-rich air, the fire can become more intense.

Different climates experience cold waves in very different ways. A temperature that is normal for places like Colorado, Ohio, or Bavaria might be catastrophic for crops in Florida, California, or parts of South America. In subtropical climates, a cold wave might be recognized at temperatures that are barely freezing. This is because plant and animal life in those areas is less tolerant of such cold. In mid-latitude zones, unexpected freezes during the growing season can kill plants during their most vulnerable stages. This leads to crop failure and can even cause famines. Such cold waves are as deadly to plants as droughts. They can also leave land at risk of future forest fires by leaving behind dead biomass.

Scientists study several patterns to understand why these waves happen. Recent research suggests a possible link between cold waves in North America and extratropical cyclogenesis over the East Atlantic. These events may be connected by large-scale atmospheric circulation patterns. Examples include Rossby wave propagation from the North Pacific or an upper-level anticyclone west of Greenland. In Europe, the advection of cold air masses from the northeast is a potential precursor signal for many cold waves. These events significantly affect the energy, health, and agricultural sectors of the European continent.

History provides many examples of extreme cold. In the 17th century, England experienced the Great Frost of 1683–84, which was the worst frost in its history. The River Thames froze to a depth of 2 feet, allowing for a Frost Fair. In 1709, Europe saw the coldest winter ever recorded. The 19th century saw many historic events, such as the 1835 Eastern cold wave where mercury thermometers froze in the Northeast. In 1836, Sydney, Australia, recorded a snowfall on June 28 with temperatures dropping to 38 degrees Fahrenheit. The year 1816 was known as the Year Without a Summer. This was caused by volcanic eruptions that reduced incoming sunlight and led to freakish summer cold snaps.

To survive these events, people use various countermeasures. In Siberia, fuel-powered machinery must often be run continually to prevent it from freezing. People may wrap internal plumbing or run water continuously through pipes to prevent freezing. In some areas, communal shelters are used to collect the elderly and the poor. Farmers use smudge pots to create smoke that prevents hard freezes in groves. They may also spray vulnerable crops with water. Paradoxically, this protects the plants because the freezing water absorbs heat from the surrounding air. People also prepare by stocking food, water, candles, and matches. However, using charcoal fires for heating inside a home is extremely dangerous due to the risk of carbon monoxide poisoning.