Extreme weather


Extreme weather or extreme climate events includes unexpected, unusual, severe, or unseasonal
weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosp ...

; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a location's recorded weather history and defined as lying in the most unusual ten percent. There is evidence to suggest that
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known event ...
is increasing the periodicity and intensity of some extreme weather events. Confidence in the attribution of extreme weather and other events to anthropogenic climate change is highest in changes in frequency or magnitude of extreme heat and cold events with some confidence in increases in heavy precipitation and increases in the intensity of droughts. Extreme weather has significant impacts on human society as well as natural ecosystems. For example, a global insurer
Munich Re Munich Re Group or Munich Reinsurance Company (german: Münchener Rück; Münchener Rückversicherungs-Gesellschaft) is a reinsurance company based in Munich, Germany. It is one of the world's leading reinsurers. ERGO Insurance Group, ERGO, a Muni ...
estimates that natural disasters cause more than $90 billion global direct losses in 2015.

Extreme weather events

Heat waves

Heat waves are periods of abnormally high temperatures and heat index. Definitions of a heatwave vary because of the variation of temperatures in different geographic locations. Excessive heat is often accompanied by high levels of
humidity Humidity is the concentration of water vapour (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapo ...

, but can also be catastrophically dry. Because heat waves 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. Severe heat weather can damage populations and crops due to potential
dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of Metabolism, metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental tempe ...

hyperthermia Hyperthermia, also known simply as overheating, is a condition where an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat In thermodynamics, heat is ...
, heat cramps, heat expansion, and
heat stroke Heat stroke, also known as sun stroke, is a type of severe heat illness that results in a body temperature greater than and confusion. Other symptoms include red skin, headache, and dizziness. There is generally a lack of sweating in classic ...
. Dried soils are more susceptible to erosion, decreasing lands available for
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentism, sedentary human civilization, whereby farming of domestication, domesticated species created food ...

. Outbreaks of wildfires can increase in frequency as dry vegetation has increased the likeliness of igniting. The
evaporation File:10. Ладење при испарување.ogv, 280px, Demonstration of evaporative cooling. When the sensor is dipped in ethanol and then taken out to evaporate, the instrument shows progressively lower temperature as the ethanol evapor ...

of bodies of water can be devastating to marine populations, decreasing the size of the habitats available as well as the amount of nutrition present within the waters. Livestock and other animal populations may decline as well. During excessive heat, plants shut their leaf pores (
stomata File:LeafUndersideWithStomata.jpg, The underside of a leaf. In this species (''Tradescantia zebrina'') the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigme ...

), a protective mechanism to conserve water but also curtails plants' absorption capabilities. This leaves more pollution and ozone in the air, which leads to higher mortality in the population. It has been estimated that extra pollution during the hot summer of 2006 in the UK, cost 460 lives. The European heat waves from summer 2003 are estimated to have caused 30,000 excess deaths, due to heat stress and
air pollution Air pollution is the presence of substances in the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gas ...

air pollution
. Over 200 U.S cities have registered new record high temperatures. The worst heat wave in the USA occurred in 1936 and killed more than 5000 people directly. The worst heat wave in Australia occurred in 1938–39 and killed 438. The second worst was in 1896. Power outages can also occur within areas experiencing heat waves due to the increased demand for electricity (i.e. air conditioning use). The
urban heat island Image:Urban heat island.svg, 300px, Mechanism of the urban heat island effect An urban heat island (UHI) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperat ...

urban heat island
effect can increase temperatures, particularly overnight.

Cold waves

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 at 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 Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...
or starvation. Cold waves often necessitate the purchase of
fodder Fodder (), also called provender (), is any agricultural food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') ...

for livestock at considerable cost to farmers. Human populations can be inflicted with
frostbite Frostbite is a skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod ex ...

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 water
pipes PIPES is the common name for piperazine-N,N′-bis(2-ethanesulfonic acid), and is a frequently used buffering agent in biochemistry. It is an ethanesulfonic acid buffer developed by Good et al. in the 1960s. Applications PIPES has two Acid dissoc ...
to freeze. Even some poorly protected indoor
plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delive ...

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 up Kaman K-MAX helicopter fighting wildfires in Utah Firefighting is the act of attempting to prevent the spread of and extinguish significant unwanted fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process ...

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
harvest Harvesting is the process of gathering a ripe crop from the field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an ...

ed economically. Such cold waves have caused
famine A famine is a widespread scarcity of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual con ...

s. 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 eruption Several types of volcanic eruptions—during which lava, tephra (Volcanic ash, ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a Volcano, volcanic vent or fissure vent, fissure—have been distinguished ...

volcanic eruption
s reduced incoming sunlight. In some cases more frequent extremely cold winter weather – i.e. across parts of Asia and North America including the
February 2021 North American cold wave The February 2021 North American cold wave was an extreme weather event that brought record cold temperatures to a significant portion of Canada, the United States and parts of northern Mexico during the first half of February 2021. The cold was c ...
can be a result of climate change such as due to changes in the Arctic. However, conclusions that link climate change to cold waves are considered to still be controversial. The JRC PESETA IV project concluded in 2020 that overall climate change will result in a decline in the intensity and frequency of extreme cold spells, with milder winters reducing fatalities from extreme cold, even if individual cold extreme weather may sometimes be caused by changes due to climate change and possibly even become more frequent in some regions.

Tropical cyclones

On June 12, 2020, the National Oceanic and Atmospheric Administration (NOAA) of the U.S. government predicted that, over the 21st Century, the frequency of tropical storms and Atlantic hurricanes would decline by 25 percent while their maximum intensity would rise 5 percent. Prior to the new study there was a decade-long debate about a possible increase of
tropical cyclones A tropical cyclone is a rapidly rotating storm, storm system characterized by a Low-pressure area, low-pressure center, a closed low-level atmospheric circulation, Beaufort scale, strong winds, and a spiral arrangement of thunderstorms that p ...
as an effect of climate change. However, the 2012
IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and international security, s ...
special 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 Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size of the resident population within their jurisdiction by a process called a ce ...

densities increase the number of people affected and damage caused by an event of given severity. The
World Meteorological Organization The World Meteorological Organization (WMO) is a List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and g ...
and the U.S. Environmental Protection Agency have in the past linked increasing extreme weather events to climate change, 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 Kerry Andrew Emanuel (born April 21, 1955) is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge, Massachusetts, Cambridge. In particular he has specialized in atmospheric convection an ...
in ''
Nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and ...
'' writes that hurricane power dissipation is highly correlated with temperature, reflecting climate change. 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 The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency within the United States Department of Commerce The United States Department of Commerce is an executive department The United ...

stated in 2004 that warming-induced by
greenhouse gas A greenhouse gas (GHG or GhG) is a gas Gas is one of the four fundamental states of matter (the others being solid, liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformat ...
may lead to the increasing occurrence of highly destructive category-5 storms. Vecchi and Soden find that
wind shear uncinus ice crystal plumes showing high-level wind shear, with changes in wind speed and direction Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind wind speed, speed and/or wind direction, direction over ...
, the increase of which acts to inhibit
tropical cyclones A tropical cyclone is a rapidly rotating storm, storm system characterized by a Low-pressure area, low-pressure center, a closed low-level atmospheric circulation, Beaufort scale, strong winds, and a spiral arrangement of thunderstorms that p ...
, also changes in model-projections of climate change. There are projected increases of
wind shear uncinus ice crystal plumes showing high-level wind shear, with changes in wind speed and direction Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind wind speed, speed and/or wind direction, direction over ...
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.

Research and attribution

Early research in extreme weather focused on statements about predicting certain events, contemporary research has focused more on attribution of causes to trends in events. In particular the field is focusing on
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known event ...
alongside other causal factors for these events. Definitions of extreme weather vary in different parts of the scientific community, changing the outcomes of research from those fields. Generally speaking, one event in extreme weather cannot be attributed to any one cause; however, certain system wide changes to global weather systems can lead to increased frequency or intensity of extreme weather events. A 2016 report from the
National Academies of Sciences, Engineering, and Medicine The National Academies of Sciences, Engineering, and Medicine (also known as NASEM or the National Academies) is the collective scientific national academy A national academy is an organizational body, usually operating with state financial sup ...
, recommended investing in improved shared practices across the field working on attribution research, improving the connection between research outcomes and weather forecasting. As more research is done in this area, scientists have begun to investigate the connection between climate change and extreme weather events and what future impacts may arise. Much of this work is done through climate modeling. Climate models provide important predictions about the future characteristics of the atmosphere, oceans, and Earth using data collected in the modern day. However, while climate models are vital for studying more complex processes such as climate change or ocean acidification, they are still only approximations. Moreover, weather events are complex and cannot be tied to a singular cause -- there are often many atmospheric variables such as temperature, pressure, or moisture to note on top of any influences from climate change or natural variability. An important record of extreme weather events is gathered statistics from around the world, which can help scientists and policymakers to have a better understanding of any changes in weather and climate conditions. These statistics can influence climate modeling as well. Statistics have shown an increase in extreme weather events throughout the 1900s and into the 2000s. In a report published by the United Nations Office for Disaster Risk Reduction (UNDRR), it was shown that there were around 6,681 climate-related events reported during 2000-2019, compared to 3,656 climate-related events reported during 1980-1999. In this report, a ‘climate-related event’ refers to floods, storms, droughts, landslides, extreme temperatures (like heat waves or freezes), and wildfires; it excludes geophysical events such as volcanic eruptions, earthquakes, or mass movements. While there is evidence that a changing global climate, such as an increase in temperature, has impacted the frequency of extreme weather events, the most significant effects are likely to arise in the future. This is where climate models are useful, for they can provide simulations on how the atmosphere may behave over time and what steps need to be taken in the present day to mitigate any negative changes. Of course, there are errors associated with statistic-based data. Over or under reporting of casualties or losses can lead to inaccuracy in the impact of extreme weather. As science and technology has improved throughout the twentieth and twenty-first centuries, some researchers attribute increases in extreme weather occurrences to more reliable reporting systems. A difference in what qualifies as ‘extreme weather’ in varying climate systems could also be argued. However, the UNDRR report shows that, although some countries have experienced greater effects, there have been increases in extreme weather events on all continents. Current evidence and climate models show that an increasing global temperature will intensify extreme weather events around the globe, thereby amplifying human loss, damages and economic costs, and ecosystem destruction.

Attribution to natural variability

Aspects of our climate system have a certain level of natural variability, and extreme weather events can occur for several reasons beyond human impact, including changes in pressure or the movement of air. Areas along the coast or located in tropical regions are more likely to experience storms with heavy precipitation than temperate regions, although such events can occur. Not every unusual weather event can be blamed on climate change. The atmosphere is a complex and dynamic system, influenced by several factors such as the natural tilt and orbit of the Earth, the absorption or reflection of solar radiation, the movement of air masses, and the hydrologic cycle. Due to this, weather patterns can experience some variation, and so extreme weather can be attributed, at least in part, to the natural variability that exists on Earth. Climatic variations such as the El Niño-Southern Oscillation or the North Atlantic Oscillation impact weather patterns in specific regions of the world, influencing temperature and precipitation. The record-breaking extreme weather events that have been catalogued throughout the past two hundred years most likely arise when climate patterns like ENSO or NAO work “in the same direction as human‐induced warming."

Attribution to climate change

In general, climate models show that with climate change, the planet will experience more extreme weather. Storms such as hurricanes or tropical cyclones may experience greater rainfall, causing major flooding events or landslides by saturating soil. This is because warmer air is able to ‘hold’ more moisture due to the water molecules having increased kinetic energy, and precipitation occurs at a greater rate because more molecules have the critical speed needed to fall as rain drops. A shift in rainfall patterns can lead to greater amounts of precipitation in one area while another experiences much hotter, drier conditions, which can lead to drought. This is because an increase in temperatures also lead to an increase in evaporation at the surface of the earth, so more precipitation does not necessarily mean universally wetter conditions or a worldwide increase in drinking water. Some studies assert a connection between rapidly warming arctic temperatures and thus a vanishing
cryosphere The cryosphere (from the Greek ''kryos'', "cold", "frost" or "ice" and ''sphaira'', "globe, ball") is an all-encompassing term for those portions of Earth Earth is the third planet from the Sun and the only astronomical object known to ...
to extreme weather in mid-latitudes. In a study published in Nature in 2019, scientists used several simulations to determine that the melting of ice sheets in Greenland and Antarctica could affect overall sea level and sea temperature. Other models have shown that modern temperature rise and the subsequent addition of meltwater to the ocean could lead to a disruption of the thermohaline circulation, which is responsible for the movement of seawater and distribution of heat around the globe. A collapse of this circulation in the northern hemisphere could lead to an increase in extreme temperatures in Europe, as well as more frequent storms by throwing off natural climate variability and conditions. Thus, as increasing temperatures cause glaciers to melt, mid-latitudes could experience shifts in weather patterns or temperatures.

Impact of human activity

Another important area of research, on top of the factors that may cause or increase the occurrence of extreme weather events, is to examine what might amplify the effects of extreme weather. One of the major influences is human activity. While burning fossil fuels is the most obvious way that humans have influenced extreme weather events, there are plenty of other anthropogenic activities that can exacerbate the effects of such events. Urban planning often amplifies flooding impacts, especially in areas that are at increased risk of storms due to their location and climate variability. First, increasing the amount of impervious surfaces, such as sidewalks, roads, and roofs, means that less of the water from incoming storms is absorbed by the land. The destruction of wetlands, which act as a natural reservoir by absorbing water, can intensify the impact of floods and extreme precipitation. This can happen both inland and at the coast. However, wetland destruction along the coast can mean decreasing an area’s natural ‘cushion,’ thus allowing storm surges and flood waters to reach farther inland during hurricanes or cyclones. Building homes below sea level or along a floodplain puts residents at increased risk of destruction or injury in an extreme precipitation event. More urban areas can also contribute to the rise of extreme or unusual weather events. Tall structures can alter the way that wind moves throughout an urban area, pushing warmer air upwards and inducing convection, creating thunderstorms. With these thunderstorms comes increased precipitation, which, because of the large amounts of impervious surfaces in cities, can have devastating impacts. Impervious surfaces also absorb energy from the sun and warm the atmosphere, causing drastic increases in temperatures in urban areas. This, along with pollution and heat released from cars and other anthropogenic sources, contributes to urban heat islands.  As temperatures continue to rise due to anthropogenic emissions, heat waves could become more common or threatening in urban areas. Additionally, high population density in cities exacerbates human loss in many extreme weather events. Overall, while human activity can have a direct impact on weather patterns, it's just as important to consider how human actions might exacerbate the effects and losses from extreme weather events. Concerning anthropogenic global warming, a study which also provides projections for future extreme heat incidences, found that the increasing probability of record week-long heat extremes occurrence depends on warming rate, rather than global warming level.


The effects of extreme weather includes, but not limited to: * Too much rain (heavy downpours), causes floods and landslides * Too much heat and no rain ( heatwave) drought and wildfires * Strong winds, such as hurricanes and tornadoes = damage to man made structures and animal habitats * Large snowfalls = avalanches and blizzards

Changes in human society

Economic cost

According to
IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations The United Nations (UN) is an intergovernmental organization that aims to maintain international peace and international security, s ...
(2011) estimates of annual losses have ranged since 1980 from a few billion to above US$200 billion (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina). The global weather-related disaster losses, 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. Yet, recent abnormally intense storms, hurricanes, floods, heatwaves, droughts and associated large-scale wildfires have led to unprecedented negative ecological consequences for tropical forests and coral reefs around the world.

Loss of life

The death toll from natural disasters has declined over 90 percent since the 1920s, according to the International Disaster Database, even as the total human population on Earth quadrupled, and temperatures rose 1.3°C. In the 1920s, 5.4 million people died from natural disasters while in the 2010s, just 400,000 did. The most dramatic and rapid declines in deaths from extreme weather events have taken place in south Asia. Where 1991 Bangladesh cyclone, a tropical cyclone in 1991 in Bangladesh killed 135,000 people, and a 1970 Bhola cyclone, 1970 cyclone killed 300,000, the similarly-sized Cyclone Amphan, Cyclone Ampham, which struck India and Bangladesh in 2020, killed just 120 people in total. On July 23, 2020, Munich Re announced that the 2,900 total global deaths from natural disasters for the first half of 2020 was a record-low, and “much lower than the average figures for both the last 30 years and the last 10 years.” A 2021 study found that 9.4% of global deaths between 2000 and 2019 – ~5 million annually – can be attributed to extreme temperature with cold-related ones making up the larger share and decreasing and heat-related ones making up ~0.91 % and increasing.

Changes in ecosystems

Extreme weather negatively affects the ecosystems through various events resulting the serious impact on the landscape and people. In many cases wildfires provide growth and rid of the abundant weeds and other dry plants that build up over time, that cause the beginnings of rampant wildfires. Although there are beneficial events from wildfires it also effects ecosystems of animals, plants, and even human societies. These events cause the ground to be more dry and in turn create more wildfires while also causing erosion that leads to dangerous landfall. Wildfires also cause a disruption in Carbon cycle, carbon cycles which can affect water quality and land settings in the area.

See also

*Heat burst *List of tropical cyclones *Lists of tornadoes and tornado outbreaks *List of weather records *Downburst *Rogue wave *Severe weather ** List of severe weather phenomena *Storm *U.S. state and territory temperature extremes *Water scarcity *Weather modification *Weather-related fatalities in the United States *Climate change *Extreme weather events of 535–536 * Year Without a Summer


External links

NOAA/NCDC Billion-Dollar Weather and Climate Disasters
The University Corporation for Atmospheric Research (UCAR)
Research forecasts increased chances for stormy weather
Purdue University study
Extreme weather
articles at ''Think Progress''
European severe weather databaseNational severe weather database browserSevere world weather overview
{{Authority control Weather hazards Severe weather and convection Effects of climate change Natural hazards Articles containing video clips