|This article may be expanded with text translated from the corresponding article in the Japanese Wikipedia. (March 2013)|
|This article may be expanded with text translated from the corresponding article in the Spanish Wikipedia. (July 2013)|
Extreme weather includes unusual, severe or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. The most commonly used definition of extreme weather is based on an event's climatological distribution: Extreme weather occurs only 5% or less of the time. According to climate scientists and meteorological researchers, extreme weather events have been rare. Some extreme weather events have been attributed to man-made global warming, with a 2012 studies indicating an increasing threat from extreme weather.
According to IPCC (2011) estimates of annual losses have ranged since 1980 from a few billion to above 200 billion USD (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina). The global weather- and climate-related disaster losses reported over the last few decades reflect mainly monetized direct damages to assets, and are unequally distributed. Loss estimates are lower bound estimates because many impacts, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and monetize, and thus they are poorly reflected in estimates of losses.
Heat waves are long periods of abnormally high temperatures. There is generally no universal definition of a heatwave because of the variation within temperatures are different in geographic locations. Along with the excessive heat, they are often accompanied by high levels of humidity. These two characteristics increase the relative temperature or heat index to dangerous levels.
Because heatwaves are not visible as other forms of severe weather are, like hurricanes, tornadoes, and thunderstorms, they are one of the less known forms of extreme weather. This severe weather phenomena can damage populations and crops due to potential dehydration or hyperthermia, Heat cramps, heat expansion and heat stroke can result in human populations. The dried soils are more susceptible to erosion, decreasing lands available for agriculture. Outbreaks of wildfires can increase in frequency as dry vegetation has increased likeliness of igniting. The evaporation of bodies of water can be devastating to marine populations, decreasing the size of the habitats available as well as the amount of nutrition presented within the waters. Livestock and other animal populations may decline as well. Power outages can also occur within areas experiencing heatwaves due to the increased demand for electricity. The urban heat island effect can increase temperatures even more, particularly overnight.
A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24 hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criterion for a cold wave is determined by the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year. Cold waves generally are capable of occurring any geological location and are formed by large cool air masses that accumulate over certain regions, caused by movements of air streams.
A cold wave can cause death and injury to livestock and wildlife. Exposure to cold mandates greater caloric intake for all animals, including humans, and if a cold wave is accompanied by heavy and persistent snow, grazing animals may be unable to reach necessary food and water, and die of hypothermia or starvation. Cold waves often necessitate the purchase of fodder for livestock at considerable cost to farmers. Human populations can be inflicted with frostbites when exposed for extended periods of time to cold and may result in the loss of limbs or damage to internal organs.
Extreme winter cold often causes poorly insulated water pipes to freeze. Even some poorly-protected indoor plumbing may rupture as frozen water expands within them, causing property damage. Fires, paradoxically, become more hazardous during extreme cold. Water mains may break and water supplies may become unreliable, making firefighting more difficult.
Cold waves that bring unexpected freezes and frosts during the growing season in mid-latitude zones can kill plants during the early and most vulnerable stages of growth. This results in crop failure as plants are killed before they can be harvested economically. Such cold waves have caused famines. Cold waves can also cause soil particles to harden and freeze, making it harder for plants and vegetation to grow within these areas. One extreme was the so-called Year Without a Summer of 1816, one of several years during the 1810s in which numerous crops failed during freakish summer cold snaps after volcanic eruptions reduced incoming sunlight.
Related to significant tropical cyclones
There has been long ongoing debate about a possible increase of tropical cyclones as an effect of global warming. However, as of March 2012, the latest IPCC report on extreme events SREX states that "there is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities."  Increases in population densities increase the number of people affected and damage caused by an event of given severity. The World Meteorological Organization and the U.S. Environmental Protection Agency have in the past linked increasing extreme weather events to global warming, as have Hoyos et al. (2006), writing that the increasing number of category 4 and 5 hurricanes is directly linked to increasing temperatures. Similarly, Kerry Emanuel in Nature writes that hurricane power dissipation is highly correlated with temperature, reflecting global warming. Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high CO2 conditions, are more intense than under present-day conditions. Thomas Knutson and Robert E. Tuleya of the NOAA stated in 2004 that warming induced by greenhouse gas may lead to increasing occurrence of highly destructive category-5 storms. Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-projections of global warming. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific. The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the warming and moistening atmospheres, and the model-projected increases in Atlantic wind shear.
- List of weather records
- Effect of sun angle on climate
- Global warming
- List of tropical cyclones
- List of tornadoes and tornado outbreaks
- Severe weather
- U.S. state temperature extremes
- Weather-related fatalities in the United States
- Rogue wave (oceanography)
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- NCDC weather events page
- Marble Bar heatwave, 1923-1924
- The Economic Costs of Extreme Weather Events on Society NOAA Economics
- Statistics of Weather and Climate Extremes The University Corporation for Atmospheric Research (UCAR)
- Research forecasts increased chances for stormy weather, Purdue University study
- Extreme weather articles at Think Progress