What Is Extreme Weather?
Extreme weather is what we call it when a particular weather event like a flash flood or a heat wave is significantly different from the average weather pattern for an area. It is important to understand these events because they can be disruptive and even deadly, harming human communities, agriculture and ecosystems.
Extreme weather can either be weather related or climate related. Weather-related extreme weather events are shorter incidents like tornadoes, deep freezes or heat waves. Climate related extreme weather events last longer or are caused by a buildup of weather-related events over time. Examples include droughts caused by long dry spells or wildfires caused by an extended drought. Extreme weather events can be caused by natural cycles like La Niña or more immediate influences like high pressure systems. However, they are becoming more likely because of the climate crisis caused by the human emission of greenhouse gasses.
Scientists typically define an extreme weather event in one of two ways, according to the U.S. Department of Agriculture’s Climate Hubs. The first looks at the likelihood of a given event occurring at a certain intensity during a specific time frame. The second focuses on whether an event passes a particular limit, i.e. if a heat wave exceeds a number of days over 100 degrees Fahrenheit.
Types of Extreme Weather
There are various types of extreme weather events that can have a serious impact on human populations.
A drought is defined as a “a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area.” What this means is that a dry spell lasts long enough to diminish the water supply or damage crops. One famous example is the Dust Bowl of the 1930s. While this is often referred to as a single disaster, it was really a series of droughts that impacted the south-central U.S. and were then exacerbated by damaging dust storms. Currently, the southwestern U.S. is in the midst of its biggest megadrought in 1,200 years, which has shrunken reservoirs, depleted Utah’s Great Salt Lake to record low levels and encouraged devastating wildfires.
A heat wave is a stretch of unusually hot weather that lasts for two or more days. To be considered a heat wave, temperatures must rise above the average for an area, so two 95 degree days in Maine would be considered a heat wave, but the same in Death Valley would not. Heat waves are often caused when hot air becomes trapped over an area by something like a high pressure system. Heat waves are actually the deadliest kind of extreme weather event, killing more U.S. residents each year on average than any other weather disaster. The blood thickens when the human body becomes overheated, forcing the heart to pump harder and putting it and other organs at risk for damage. The deadliest heat wave on record was a 2010 heat wave that killed as many as 56,000 people in Russia.
Hurricanes, Typhoons and Cyclones
A tropical cyclone is a type of storm that forms over tropical or subtropical waters. It consists of a rotating circle of clouds and thunderstorms. These weather systems are defined by their maximum sustained wind speed. A system with a wind speed below 39 miles per hour is a tropical depression. A system with a wind speed above this is a tropical storm. A storm with a wind speed 74 miles per hour or higher is a tropical cyclone. Tropical cyclones are called hurricanes in the North Atlantic, central North Pacific and eastern North Pacific and typhoons in the Northwest Pacific. In the South Pacific and Indian Ocean, all storms are called tropical cyclones regardless of wind speed. Tropical cyclones are usually accompanied by heavy winds, large waves, heavy rains and flooding. The deadliest tropical cyclone was Cyclone Bhola, which killed as many as 500,000 people in 1970 in what is now Bangladesh. The storm was so deadly because of a storm surge that swamped low-lying islands and tidal flats in the Bay of Bengal. The deadliest hurricane in U.S. history was the Great Galveston Storm of 1900, which saw wind speeds greater than 135 miles per hour and a storm surge of 15 feet. It claimed between 6,000 and 12,000 lives. The second deadliest was Hurricane Maria, which killed 2,975 people in Puerto Rico in 2017.
A tornado is a thin, rapidly rotating column of air extended by a thunderstorm towards the ground. They are one of the most violent effects of atmospheric storms. Also called twisters, they can have wind speeds greater than 250 miles per hour and clear a path a mile wide by 50 miles long. The most destructive tornadoes typically come from large and long-lasting thunderstorms called supercells. Tornadoes occur all over the world, but are most common in the U.S., where there are about a thousand every year, which cause around 80 deaths and more than 1,500 injuries. Tornado Alley is the name the media uses to refer to a part of the central U.S. where violent tornadoes tend to occur. However, tornadoes have been recorded in all 50 states and generally shift from the Southeast in Winter to the south and central Plains in May and June to the northern Plains and Midwest in early summer. The deadliest tornado in U.S. history was the Tri-State Tornado of 1925, which cut a 219-mile long swathe through Missouri, Illinois and Indiana. It killed 695 people and injured 2,027. In a recent example of a tornado outbreak, at least 50 twisters killed more than 100 people in Arkansas, Illinois, Indiana, Mississippi, Missouri, Ohio, and Tennessee and Kentucky in December of 2021.
A wildfire is an unplanned, uncontrolled fire that burns in a natural area like a forest or grassland. They can start either because of a natural occurrence like a lightning strike or because of human activity. However, their spread is determined by external conditions such as high temperatures, high wind speeds and low precipitation that leaves lots of dried vegetation as fuel. Wildfires are actually a natural and helpful part of several ecosystems. Some tree cones need the heat from fires in order to open and release their seeds and chaparral plants need fire for their seeds to germinate. Wildfires can also kill insects and disease and clear out dead vegetation to make way for new growth. However, in some places an increase in fire activity is putting a strain on both ecosystems and human communities. In the Southwestern U.S., a history of fire suppression led to a build up of potential fuel, which has combined with higher temperatures and drought to cause more frequent and extreme fires in recent years. The Camp Fire in 2018 destroyed almost the entire town of Paradise and was the deadliest and most destructive fire in California history. Unprecedented bushfires in Australia in 2019 and 2020 killed or displaced around three billion animals.
Winter storms are a life-threatening combination of heavy snow, blowing snow and dangerous wind chill. A blizzard is a type of winter storm that combines heavy wind with blowing snow to severely reduce visibility. An ice storm occurs when at least a quarter of an inch of ice accumulates on surfaces. This can make driving or walking very dangerous and cause tree branches or power lines to snap. The deadliest winter storm in U.S. history was the Great Blizzard of 1888, which killed more than 400 people in Connecticut, Massachusetts, New Jersey and New York. It dumped 40 to 50 inches of snow and buried trains and buses. A famous ice storm occurred in New England in December of 2008, cutting off power to more than a million people.
Extreme Weather and the Climate Crisis
The climate crisis is making many extreme weather events both more frequent and more severe. A new scientific field called “extreme event attribution” has emerged to assess the human fingerprints on any particular extreme weather event, such as a storm or heat wave. Carbon Brief drew on more than 350 peer-reviewed attribution studies to create a map of 405 extreme weather events or trends. The research had found that 70 percent of them were made more likely or more severe by human-caused climate change. There are several reasons that climate change has this effect, and they vary depending on the weather event in question.
The climate crisis raises the likelihood of drought because higher temperatures lead to more evaporation, reducing surface water and drying out soils and vegetation. Further, increased winter temperatures means that less precipitation falls as snow in some areas. Even if the same amount of precipitation falls overall, this can still lead to drought because some water systems depend heavily on the spring melt from mountain snowpacks. The current megadrought in the U.S. West is calculated to be 42 percent more extreme because of the climate crisis.
The connection between climate change and heat waves is perhaps the most straightforward. As global temperatures rise, periods of extreme heat naturally increase. In the last decade, daily record highs in the continental U.S. have occurred twice as often as record lows. Carbon Brief considered 122 studies that looked at extreme heat events or trends and found that 92 percent of the events studied were made more likely or severe because of the climate crisis. For example, the heat wave that baked France in 2019 was found to be 10 to 100 times more likely because of the burning of fossil fuels.
Hurricanes, Typhoons and Cyclones
The climate crisis has several impacts on tropical storms. Warmer sea surface temperatures make storms both stronger and wetter. NOAA has predicted that the number of the strongest Category 4 and 5 hurricanes will increase as the climate warms. Further, more evaporation leads to more moisture in the air, increasing intense rainfall. Scientists estimated that the climate crisis made 2018’s Hurricane Florence 50 percent wetter. Sea level rise also increases the impact of hurricanes because the storm surge does not have as far to travel. Hurricane Harvey’s storm surge, for example, gained half a foot because of a combination of sea level rise and land sinking due to oil drilling. How climate change will impact the overall frequency of hurricanes is less clear.
The impact of the climate crisis on tornadoes is also uncertain. As far as scientists can tell, there has been no increase in the number of strong tornadoes in the U.S. in the past few decades. There have been more incidents of tornadoes occurring in clusters, and there is some evidence that the overall power of tornadoes is increasing, but there is no clear link between these trends and the climate crisis. There is also evidence that the traditional “tornado alley” is moving eastward from the Great Plains to the Midwest and Southeast. Scientists say it is possible that climate change is behind the shift, but more research is needed.
Wildfire risk is increasing for much the same reason as drought. Climate change raises temperatures, increases the amount of dry vegetation that serves as wildfire fuel and reduces the amount of water available. This means that when fires ignite, they are more likely to burn larger and with greater intensity. They are also becoming more frequent and the length of the fire season is getting longer. In the U.S. West, the number of large fires has doubled between 1984 and 2015. Scientists calculated that the climate crisis made Australia’s 2019 and 2020 bushfire season at least 30 percent more likely.
While climate change may lead to warmer winters overall, it can still increase the amount of snow that falls during winter storms. This is because it increases the amount of moisture in the atmosphere, which will fall as snow if temperatures dip below freezing. Further, there is some debate as to whether or not Arctic warming destabilizes the jet stream, leading Arctic air to travel south to cause infamous “polar vortex” cold snaps.
Effects of Extreme Weather
Extreme weather can have serious and lasting impacts beyond the initial wildfire, flood or storm. In the immediate aftermath of a storm, access to food, water and shelter are reduced, putting survivors at risk from malnutrition and dehydration. When the power goes out, people often turn to carbon-monoxide-powered generators, which can increase the risk of carbon monoxide poisoning.
Disease is another major risk. Water resources can be contaminated by drought–which increases the spread of “effluent pathogens”–or flooding, which can spill wastewater into the drinking supply. For example, a cholera outbreak followed in the wake of Cyclone Idai, which devastated Mozambique, Zimbabwe and Malawi in 2019. A major concern during the 2020 hurricane and wildfire seasons was whether or not evacuees would contract COVID-19 in crowded shelters. One Harvard study also found that people exposed to wildfire smoke were more likely to both catch and die from the coronavirus.
Both warm and cold weather can also cause long-lasting health implications. The climate crisis has increased the numbers of crop pests, which in turn has prompted farmers to use more pesticides, which both decrease the nutritional value of food and threaten human health. The spread of the mold that creates the liver-damaging toxin aflatoxin has also been linked to the climate crisis. Cold weather can increase the risk of pneumonia, influenza, norovirus and heart disease.
Extreme weather events can also have a major impact on the economy. Europe lost nearly half a trillion euros because of extreme weather events from 1980 to 2000. Twenty extreme weather events in 2021 cost the U.S. at least $145 billion dollars. Individuals and communities can take a long time to recover from the hit of a major disaster. For example, New Orleans’ Lower Ninth Ward, which was hit hard by Hurricane Katrina in 2005, was still full of vacant lots 14 years later. A single grocery store served a population of 1,200.
Extreme Weather and Environmental Justice
Hurricane Katrina is an example of the truism that “there is no such thing as a natural disaster.” This means that, even if a particular extreme weather event is entirely triggered by natural causes, who suffers the consequences of that event is often based on preexisting social inequalities. In the case of Hurricane Katrina, wealthier, generally white residents had access to the cars and funds needed to evacuate while poorer communities of color did not. Because of historic racism, white communities in New Orleans tended to live on higher ground than Black communities, and therefore a Black homeowner in the city was more than three times more likely to have their home flooded than a white homeowner. More than ten years later, 96,000 fewer Black people lived in the city than before the storm.
The environmental justice aspect of extreme weather events is only exacerbated when those events are caused or worsened by human-generated climate change. A 2018 study found that the countries that did the least to contribute to the climate crisis in the form of greenhouse gas emissions and are already more vulnerable to extreme weather events are the most likely to see increased temperature variability. Indigenous people worldwide are more likely to be impacted by extreme events because they tend to rely more on natural resources, while poorer communities also already lack the infrastructure to withstand weather damage. To address these inequalities on a global scale, developing countries have called on wealthier nations to help them pay for the losses and damages from climate-fueled extreme weather events and other longer-term climate impacts. At the most recent UN COP26 climate conference in Glasgow last November, countries recognized that poorer nations were experiencing greater losses and damages because of the climate crisis, but they did not establish a fund to help cover these losses, largely due to opposition from the U.S., Europe and other wealthy nations.
The severity and frequency of extreme weather events are only expected to increase this century as the climate crisis persists. Many places will see more periods of extreme heat. While overall precipitation is expected to decrease, heavy rainstorms are expected to increase. Drought is expected to become more frequent and severe in places that already see low precipitation. To respond to this risk, it is important to both mitigate and adapt. Mitigation means reducing greenhouse gas emissions as promptly as possible. Adapting means planning for the changes that are already underway or locked in. This means accurately assessing the risk of extreme weather events by looking at recent trends and using climate models to see whether certain events are more likely to occur in certain areas in the future. Adaptations can range from building up oyster reefs to protect New York City from future storm surges to planting trees to reduce the impact of heat waves on cities. Understanding the link between climate change and extreme weather events is therefore essential for making sure they harm as few people and communities as possible going forward.