Extreme weather

Sometimes weather is very unusual.

It can be much hotter than usual. This is called a heat wave. It can also be much colder. These are called cold waves.

These events can be very strong. They can change how plants grow. They can even change how much water is in the ground. Some storms bring a lot of rain.

Extreme weather can be a big surprise.

Extreme weather is weather that is very unusual for a place.

It is much hotter, colder, or wetter than what is normal. Scientists look at weather history to decide what is extreme.

Heat waves are long periods of very hot weather. They can be dangerous to people and animals. Heat waves can also dry out the soil. This makes it hard for crops to grow. In very hot weather, plants close tiny holes in their leaves. This helps them save water.

Cold waves happen when the air cools down very fast. This can happen in just one day. Cold waves can freeze water pipes in homes. They can also hurt plants and farm animals.

Some storms bring a lot of heavy rain. This is called heavy precipitation. Changes in the world's weather systems can make these events happen more often. Climate change might make some extreme weather more intense. Rising temperatures can also make heavy rain events more severe. This happens because more water vapor stays in the air.

Extreme weather describes weather that is unusual for a specific place and time.

Scientists use historical weather records to decide what counts as extreme. An event is often called extreme if it is as rare as the 10th or 90th percentile of observations. This means it sits at the very edges of what normally happens. Some events are called severe weather because they pose risks to life or property. Extreme weather can include heat waves, cold waves, droughts, or heavy precipitation. These events can cause floods, landslides, and damage to human health or the economy.

Heat waves are long periods of abnormally high temperatures.

These events can be very dry or have high humidity. When it is too hot, plants shut their leaf pores, called stomata, to save water. This can also leave more pollution and ozone in the air. Heat waves can damage crops and lead to wildfires because vegetation becomes dry. They can also cause power outages when many people use air conditioning at once. In cities, an effect called the urban heat island can make temperatures even higher at night.

Cold waves happen when the air cools down very quickly. The U.S. National Weather Service defines a cold wave as a rapid temperature fall within 24 hours. These waves are formed by large, cool air masses moving through a region.

Extreme cold can freeze water pipes and cause them to rupture. It can also kill plants during their early growing stages, which sometimes leads to famine. Animals may struggle to find food if heavy snow covers the ground. Even fires can become more dangerous during extreme cold because water mains might break.

History shows us how powerful these weather events can be. The worst heat wave in the United States occurred in 1936 and killed over 5,000 people. In Europe, the summer of 2003 saw an estimated 30,000 excess deaths from heat and pollution. Australia also had a very bad heat wave in 1938–39 that killed 438 people. There was also a famous event called the Year Without a Summer in 1816. During that time, volcanic eruptions reduced sunlight and caused freakish summer cold snaps. These snaps caused many crops to fail.

Many things influence how often extreme weather happens. One cause is natural climate variability, such as the El Niño-Southern Oscillation.

However, changes to global weather systems can increase how intense these events are. Climate change may make some extreme weather more frequent. For example, rising temperatures can lead to more water vapor in the air. This can make heavy rainfall events even more severe. Human activities like building homes on floodplains can also make the effects of these storms worse.

Extreme weather refers to atmospheric events that are unusual for a specific location and time of year.

Scientists identify these events by looking at a location's recorded weather history. An event is often classified as extreme if it reaches the 10th or 90th percentile of a probability density function. This means the event is as rare as, or rarer than, most observations in that area. While extreme weather describes these rare occurrences, "severe weather" is a specific term used by the World Meteorological Organization. Severe weather refers to any weather aspect that poses risks to life or property. It may also require the intervention of authorities to manage the situation.

Extreme weather can take many different forms depending on the region. Common types include heat waves, cold waves, droughts, and heavy precipitation. Storm events, such as tropical cyclones or tornadoes, also fall into this category.

These events can trigger natural hazards like floods and landslides. They also create significant social costs by impacting human health and the economy. Some human activities can make these impacts even worse. For example, building homes on floodplains or destroying wetlands can increase the damage from storms. Poor urban planning can also exacerbate the effects of extreme weather on society.

Heat waves are periods characterized by abnormally high temperatures and a high heat index. They can be extremely dry or accompanied by high humidity. These events can lead to several biological and environmental problems. To conserve water, plants will shut their stomata, which are small pores in their leaves. While this protects the plant from dehydration, it also stops the plant from absorbing nutrients effectively. This process can lead to higher levels of ozone and pollution in the air. In the United Kingdom, extra pollution during the summer of 2006 was estimated to have cost 460 lives.

In the summer of 2003, European heat waves caused an estimated 30,000 excess deaths due to heat stress and air pollution.

Historical data shows the massive scale of heat-related mortality. The most severe heat wave in the United States occurred in 1936 and killed more than 5,000 people directly. In Australia, the worst heat wave happened during 1938–39 and resulted in 438 deaths. Heat waves also impact infrastructure and ecosystems. They can cause power outages because the demand for air conditioning increases electricity use. In cities, the "urban heat island" effect can cause temperatures to stay high even overnight. Additionally, dry vegetation increases the likelihood of wildfires, and evaporating water bodies can destroy marine habitats.

Cold waves are distinguished by a rapid cooling of the air. The U.S. National Weather Service defines a cold wave as a rapid fall in temperature within a 24-hour period. These waves are formed by large, cool air masses that move over certain regions.

Extreme cold can cause serious damage to property and life. For instance, water in poorly insulated pipes can freeze and expand, causing them to rupture. This can also break water mains, making it harder for firefighters to use water during fires. For animals, cold waves can lead to death from hypothermia or starvation if heavy snow prevents them from reaching food. In humans, prolonged exposure can result in frostbite and damage to internal organs.

Extreme cold has also caused major historical food shortages. In 1816, an event known as the "Year Without a Summer" occurred. Volcanic eruptions had reduced the amount of incoming sunlight, causing freakish summer cold snaps. These snaps led to widespread crop failures and famines. While some research suggests climate change might lead to milder winters and fewer cold-related deaths, the topic remains complex. A 2023 study noted that while weak extreme cold events are decreasing in the Northern Hemisphere, strong events are actually increasing in places like Siberia and Canada.

Understanding the causes of extreme weather requires looking at complex global systems. Generally, a single extreme weather event cannot be blamed on just one cause. Instead, they are influenced by natural climate variability, such as the El Niño-Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO).

However, system-wide changes can increase how often or how intense these events become. Climate change is a major factor that scientists study through extreme event attribution. Rising global temperatures can increase the amount of water vapor in the atmosphere. This can make heavy rainfall and precipitation events much more severe. Scientists use climate models to compare current events to models of climates without man-made drivers to understand these connections.