short essay about extreme weather

Extreme Weather and Climate Change

As the climate changes, the frequency and intensity of extreme weather events are increasing.

As Earth’s climate changes, it is impacting extreme weather across the planet. Record-breaking heat waves on land and in the ocean, drenching rains, severe floods, years-long droughts, extreme wildfires, and widespread flooding during hurricanes are all becoming more frequent and more intense.

Human actions since the Industrial Revolution, primarily the burning of fossil fuels, have caused greenhouse gases to rapidly rise in the atmosphere. As carbon dioxide, methane, and other gases increase, they act as a blanket, trapping heat and warming the planet. In response, Earth’s air and ocean temperatures warm. This warming affects the water cycle, shifts weather patterns, and melts land ice — all impacts that can make extreme weather worse.

According to the Intergovernmental Panel on Climate Change (IPCC)’s Sixth Assessment Report released in 2021, the human-caused rise in greenhouse gases has increased the frequency and intensity of extreme weather events. NASA’s satellite missions, including the upcoming Earth System Observatory , provide vital data for monitoring and responding to extreme weather events.

What are the effects of climate change on extreme weather?

Research says all the risks from these extreme weather events will escalate the more the planet warms. However, IPCC’s Sixth Assessment Report also describes some climate change mitigation strategies, technological developments, and methods for reducing greenhouse gas emissions.

How do scientists determine if changes in extreme weather events are linked to climate change?

Scientists use a combination of climate models (simulations) and land, air, sea, and space-based observations to research how extreme weather events change over time. First, scientists examine historical records to determine the frequency and intensity of past events. Many of these long-term records date back to the 1950s, though some start in the 1800s. Then scientists use climate models to see if the number or strength of these events is changing, or will change, due to increasing greenhouse gases when compared to what has happened historically.

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What Can We Do About Extreme Weather?

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Even without climate change, more people would be faced with the challenges of extreme weather events. That is because the human population continues to grow, our patterns of land use continue to change, and more and more of us are in the pathway of extreme weather events. A recent New York Times piece reported on a Gallup poll finding that one-third of all Americans have been exposed to extreme weather events since 2020. According to New York Times reporter Derrick Bryson Taylor:

“Thirty-three percent of U.S. adults said they had been affected by extreme weather since 2020… according to the survey , which was based on interviews conducted last month with about 1,000 adults living in all 50 states and Washington, D.C. Hurricanes and winter weather, such as snow, ice storms and blizzards, were the most common extreme weather events cited, followed by extreme heat and floods.”

While we experienced extreme weather events before climate change, climate change has made extreme weather more frequent and intense. Climate models in the late twentieth and early twenty-first centuries predicted impacts such as sea-level rise and extreme weather, but unlike other environmental problems such as toxic waste and air pollution, the causes were global, and the impacts were in the future. The resulting climate denial created a different type of environmental politics than the traditional politics that resulted from pollution with a visible local impact. In the 1970s, environmental policy was forged by consensus politics fueled by a threat that was obvious and undeniable. Today, it appears that there is a growing acceptance of “climate attribution science,” with more and more people accepting the notion that all this wacky weather is somehow related to climate change. That connection by the public could change the politics of climate change. The Gallup poll indicates that those who experience extreme weather tend to see climate change differently than those who have not. According to Taylor :

“…researchers found that attitudes about climate change were closely associated with personal experience with an extreme weather event. Sixty-three percent of those who had been affected by extreme weather said they worried “a great deal” about global warming, compared with 33 percent who had not been affected by extreme weather. Sixty-four percent of those who had been affected by extreme weather said that climate change would pose “a serious threat” to their way of life during their lifetime, compared with 36 percent who had not been affected by extreme weather. Sixty-seven percent of people who had lived through an extreme weather event, and 48 percent of those who had not, said that the government was not doing enough to protect the environment.” 

The massive disruption caused by extreme weather and the climate-related explanation for these events may change the politics of climate change, and climate may start to act more like traditional environmental issues. The connection between cause and impact is being made because the impacts can now be seen and felt. However, unlike traditional environmental problems, the causes are not only local. The policy prescriptions called for are more complex than those required by traditional environmental issues. Most forms of air pollution, water pollution and toxic releases can be addressed through rules and technology that are local, state-wide, and national. They are largely within the borders of sovereign nations. Climate change crosses borders because we share a common atmosphere, and greenhouse gasses created in one place impact the entire world.

One of Gallup’s most interesting findings is that the impact of experiencing extreme weather on attitudes toward climate change cuts across party lines. According to Gallup’s Jeffrey M. Jones:

“…when respondents’ partisanship is taken into account, victims of extreme weather are more likely than nonvictims to express concern about climate change. In most cases, there is a double-digit gap in climate-change attitudes between victims and nonvictims within each party group. For example, 79% of Democrats and Democratic-leaning independents who have personally been affected by an extreme weather event worry a great deal about global warming, compared with 60% of Democrats who have not had such an experience. Republicans and Republican leaners are far less likely to be concerned about global warming, but there is a 15-percentage-point gap in concern between Republicans who have (28%) and have not (13%) experienced extreme weather.”

Since extreme weather events are happening more frequently, we can expect the impact of these events on concern about climate change will increase over time. (Talk about learning a lesson the hard way.…) While this indicates that support for climate policy will increase, what can we actually do to respond to this concern about climate and extreme weather?

The approach to climate policy cannot be limited to prevention as it might in some areas of environmental policy because no single jurisdiction can prevent the problem. Still, America’s role as a global leader requires that we set an example and work to mitigate greenhouse gas pollution and develop technologies that can achieve that goal throughout the world. But in the short run, we also need to adapt to the new conditions caused by climate change. We must develop institutional mechanisms that enable communities to recover and rebuild in the aftermath of extreme weather events. We need to reconceptualize these events as routine occurrences requiring a predictable response, not as emergencies that are treated as rare and unusual.

Part of the issue of storm recovery is that our homes are more connected and more dependent on collective infrastructure than ever. While some homes might own a water well and water pump and possibly a septic tank or septic field, most Americans are connected to central water, sewage, communication, and electrical systems. Our homes, particularly due to the use of drywall, are easily damaged by floods. An absence of electricity can cause many crucial home systems to fail, leaving homes uninhabitable. The creature comforts we take for granted make recovery from extreme weather events complicated and expensive.

Due to the increasing frequency of extreme weather events, we need to develop private and publicly subsidized systems of insurance that pay the costs of reconstruction after disasters occur. Inevitably this will raise the already high cost of housing — which includes growing fees for insurance and taxes. Enacting a system of federally subsidized reconstruction insurance is politically infeasible at present but inevitable if current patterns of extreme weather persist. When such a system is finally put in place, it is critical that rates are progressive and guard against anything that increases homelessness.

In addition to private household and business reconstruction, we must also develop programs and revenue streams for infrastructure resilience and reconstruction. Schools, libraries, transportation, energy, water, communication, waste, and sewage infrastructure need to be made more weather-proof and, when damaged or destroyed, must be eligible for federal reconstruction grants. And yes, our federal tax rates must go up to pay for all of this.

Currently, weather disasters are treated as special rather than routine events. When disaster strikes, federal funding must be allocated through the theatrical spectacle of our dysfunctional Congress while victims sleep in shelters or on the couches of friends or family. The delay in funding causes pain and hardship. Children suffer as schooling is disrupted and the security of home is suddenly upended. While we have no control over nature and storms, we have a great deal of control over how we respond, recover, and rebuild.

As Mark Twain used to say (quoting someone named Charles Dudley Warner), “Everybody talks about the weather, but nobody does anything about it.” Well, we still can’t do anything to change weather, and hopefully, we are never arrogant enough to try that type of geoengineering, but we do need to predict weather, prepare for it, respond to it and learn how to rebuild after its destruction passes. The experience of extreme weather affects our view of how the world works. Objective facts that we experience personally are resistant to disinformation or ideology. Air pollution policy was a response to smog, and water pollution policy was a response to rivers that smelled bad and even caught fire. Perhaps climate change policy will be a response to our growing experience with extreme weather events.

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Why we find extreme weather so fascinating

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When climate change leads the news, it’s often down to a hurricane, heatwave or flood. And, judging by our most widely read environment stories over the past decade, extreme weather really is one of the main ways the public (or at least our readers) learns about climate breakdown.

This roundup of The Conversation’s climate coverage comes from our weekly climate action newsletter . Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. Join the 30,000+ readers who’ve subscribed.

The movie Twisters is released this week, a remake of the 1996 film with an added “s”. Simon Dickinson of the University of Plymouth says the fact Hollywood commissioned a remake is further evidence that “people are fascinated by extreme weather and the devastation it can cause”.

Dickinson explains there is a deep underlying psychology behind this, beyond people simply wanting to see stuff crash and burn. For him, people are interested in extreme weather and watch movies and videos of hurricanes, tornadoes and so on, “because they connect us to people, places and ideas. Sometimes, this is about being able to visualise concepts we’ve heard about but never seen with our own eyes.”

Read more: Twisters follows a superstar storm chaser – obsession with extreme weather has a deep underlying psychology

He recently conducted a study examining why people were watching live footage of hurricanes and storms on YouTube:

I found people wanting to see things they’d repeatedly heard reference to, such as the eye of the storm or the exact moment a hurricane made landfall. In one discussion in the comments, people wanted the wind to stop because they were only there to see if they could witness an ‘eye’. For these people, videos of extreme moments helped connect what they’ve been told with what they could see (even if only through a screen).

This will feels familiar to anyone who, like me, has been down a tornado rabbit hole on YouTube to see what the fastest winds on Earth might actually involve. (Check out this particularly harrowing video of a father and daughter surviving a twister in their shelter in Illinois, then emerging outside just 90 seconds later to find their neighbourhood in ruins ).

Climate change is, of course, the main concept that extreme weather helps people visualise. None of us can “see” 1°C of warming, but we can all watch small islands being flattened or homes being flooded.

In the big picture, it’s safe to say a warmer world means more extreme weather. But that “does not mean all extreme weather events are being made stronger or more frequent”, says Friederike Otto, a climate scientist and co-founder of the World Weather Attribution project, which investigates to what extent climate change has influenced particular episodes of extreme weather. In 2020, she described how scientists were increasingly able to provide climate–weather attribution within the news cycle .

These “rapid attribution studies” are important, she writes, “as they provide scientific evidence while the event is still in the news and everyone is still paying attention – not months later after the academic peer-review process.”

To help address [controversy over the lack of peer-review], rapid attribution studies use peer-reviewed methods, make data publicly available, and regularly submit to peer-review journals after the fact.

Read more: Yes, climate change can affect extreme weather – but there is still a lot to learn

All this means we can state the links between a given hurricane or heatwave and climate change with more certainty than ever. So are these extreme weather “events” a useful moment to talk about climate change?

Joshua Ettinger, a climate communication expert at the University of Oxford, researches how extreme weather can reduce the “psychological distance” associated with climate change. “While climate change can feel abstract and vague,” he writes , “extreme weather is something people can experience firsthand.”

People won’t necessarily draw a link between the two, however. Ettinger says that research offers “contrasting results”:

Some studies have found that extreme weather events lead to an increased belief that human-driven climate change is occurring and greater support for climate action. Others find no effects or suggest that these effects are only temporary.

But you can make a difference, says Ettinger. He points out that simply talking about climate change is a good way to inspire climate action, and that extreme weather – whether seen on TV or experienced first-hand – provides a useful conversation starter. “We can use these moments as opportunities to engage our families, friends and communities in discussions about how climate change may relate to these events, and what we can do about it.”

He notes a few guidelines for these discussions. When talking to someone about a hurricane, heatwave or flood, “affirm the validity of their emotional response – whether they are afraid, angry, hopeful or worried. There is no one right way to feel about climate change, so listen to what they have to say and then share your own perspective too.”

You might be accused of “politicising” the weather. Ettinger suggests how you can (respectfully) push back against this claim:

This argument is a discourse of climate delay [which tries] to shut down climate discussions and cast doubt on the need to act very quickly. These arguments disingenuously assert that acting on climate is too expensive, too late, or that someone else should take care of it – and they are becoming increasingly common. If we shouldn’t discuss climate change when extreme weather occurs, then when is the right time? … If talking about climate change politicises the weather, so be it.

Read more: Extreme weather events are exactly the time to talk about climate change – here's why

Outside of work, I try not to rant about climate change too much, and instead gently guide things in that direction. Perhaps you do something similar. These are tough but worthwhile conversations.

Dickinson, writing about Twisters, says the big challenge for scientists is to “harness this fascination in a way that stimulates knowledge and behavioural change beyond the small window of the event itself”. Hopefully, this newsletter has helped in that regard.

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How climate change worsens heatwaves, droughts, wildfires and floods

More than 70 million people in the US are under heat alerts this week, with extreme temperatures as high as 105F (41C) forecast in some areas.

Scientists say many extreme weather events are becoming more frequent and intense as a result of climate change.

1. More extreme rain

For every 1C rise in average temperature, the atmosphere can hold about 7% more moisture .

This can result in more droplets and heavier rainfall, sometimes in a shorter space of time and over a smaller area.

Globally, heavy rainfall events have become more frequent and intense over most land regions due to human activity, according to the UN's climate body, the IPCC .

It says this pattern will continue with further warming.

Scientists assess whether individual extreme weather events can be attributed to climate change by considering both natural and human causes .

In the case of the intense rainfall which fell in Dubai, the United Arab Emirates (UAE) and Oman in April 2024, it was difficult to conclude exactly how much of a role climate change played.

Heavy rain in this region is rare, which offers researchers fewer historical comparisons.

But these types of events have become 10-40% heavier , and climate change is the most likely explanation, according to the World Weather Attribution (WWA) group.

In May 2024, southern Brazil experienced heavy rains which lead to widespread flooding, displacing about 150,000 people.

The Rio Grande do Sul region that was hit is particularly vulnerable to heavy rains, as it is the meeting point of tropical and polar air masses.

But climate expert Francisco Eliseu Aquino told the AFP news agency that "these interactions [have] intensified with climate change".

Scientists believe the heavy rainfall which caused deadly flooding in northern Libya in September 2023 was made up to 50 times more likely by climate change .

Years of political instability in the region also hampered preparations for such events.

2. Hotter, longer heatwaves

Even a small increase in average temperatures makes a big difference to heat extremes.

As the range of daily temperatures shifts to warmer levels, hotter days are more likely and more intense.

In April 2024, temperatures in Mali hit 48.5C during an extreme heatwave across the Sahel region of Africa, which was linked to increased hospitalisations and deaths.

This level of heat would not have been possible without human-caused climate change , the WWA found, and will become more common as the world continues to warm.

In the UK, temperatures topped 40C for the first time on record in July 2022, causing extensive disruption . This would have been extremely unlikely without climate change , the WWA says.

Heatwaves are also becoming longer in many places, including the UK .

This can happen as a result of heat domes , which are areas of high pressure where hot air is pushed down and trapped, causing temperatures to soar over large areas.

One theory suggests that higher temperatures in the Arctic - which has warmed nearly four times faster than the global average - are causing strong winds called the jet stream to slow, increasing the likelihood of heat domes .

A heat dome is expected to hit the western part of the US later this week - affecting more than 34 million residents across California, Nevada, Utah and Arizona.

Forecasters predict temperatures to be 5.5-11C (10-20F) above normal, potentially posing a risk to human health and the environment from resulting wildfires.

• Is the UK getting hotter?
• Life at 50 degrees

3. Longer droughts

Linking climate change with specific individual droughts can be difficult.

The availability of water depends on more than just temperature and rainfall, with natural weather systems also playing a key role. This was the case with drought in southern Africa in early 2024 .

But heatwaves fuelled by climate change can worsen droughts by drying out soil. This makes the air above warm up more quickly, leading to more intense heat.

During periods of hot weather, increased demand for water, especially from farmers, puts even more stress on the water supply.

In parts of East Africa, there were five failed rainy seasons in a row between 2020 and 2022, as the region suffered its worst drought for 40 years. This displaced 1.2 million people in Somalia alone.

Climate change has made droughts like this at least 100 times more likely , according to the WWA.

Human-caused warming was also the main driver of the Amazon rainforest's worst drought in at least half a century in the second half of 2023.

4. More fuel for wildfires

Fires happen naturally in many parts of the world . It's difficult to know if climate change has caused or worsened a specific wildfire because other factors are also relevant, such as changing land use.

But climate change is making the weather conditions needed for wildfires to spread more likely, the IPCC says .

Extreme, long-lasting heat draws more moisture out of soils and vegetation.

These tinder-dry conditions provide fuel for fires, which can spread at an incredible speed, particularly if winds are strong.

Canada experienced by far its its worst wildfire season on record in 2023.

Climate change more than doubled the likelihood of the extreme "fire weather" conditions in eastern Canada in May and June 2023, which helped fires to spread, the WWA says .

Rising temperatures may also increase the likelihood of lightning in the world's northernmost forests, triggering fires.

The combined effects of shifting land use and climate change mean extreme wildfires are projected to become more frequent and intense in future globally, according to the UN Environment Programme (UNEP).

The number of the most extreme fires may rise by up to 50% by 2100, UNEP suggests.

• How do wildfires start?

The Influence of Climate Change on Extreme Environmental Events

Climate change affects global temperature and precipitation patterns. These effects, in turn, influence the intensity and, in some cases, the frequency of extreme environmental events, such as forest fires, hurricanes, heat waves, floods, droughts, and storms.

Climatology, Earth Science, Ecology

Boise National Forest Fire

Research shows human-caused climate change has worsened the risk of extreme weather events like the wildfires of the western United States, such as this forest fire in the Boise National Forest, Idaho.

Photograph by David R. Frazier Photolibrary, Inc./Science Source

Climate change caused by the emission of greenhouse gases from human activities affects global temperature and precipitation . Records from the Intergovernmental Panel on Climate Change indicate that the global average temperature has increased by at least 0.4 degrees Celsius (0.72 degrees Fahrenheit) since the 1970s, and that by 2100, it could increase to around 4 degrees Celsius (7.2 degrees Fahrenheit) above preindustrial temperatures. While the global effects of climate change may seem too small to be noticed by people living around the world, we have already experienced the effects of climate change through severe weather events, including forest fires, hurricanes , droughts , heat waves, floods, and storms. Computer modelling of real data has shown that the frequency and intensity of these events are influenced by climate change. There is a distinction that needs to be made when it comes to the relationship between climate change and extreme environmental events: Climate change has not been proven to directly cause individual extreme environmental events, but it has been shown to make these events more destructive, and likely happen more frequently,than they normally would be. This drastic change is due to the increase in greenhouse gas emissions—primarily through the burning of fossil fuels for transportation, heat, and electricity—in the past 150 years. Greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, trap heat within Earth’s atmosphere, making the planet warmer. A warmer atmosphere affects the water cycle because warmer air can hold more water vapor . In fact, the air’s capacity to hold water vapor increases by 7 percent with an increase in temperature of 1 degree Celsius (1.8 degrees Fahrenheit). This, along with warmer ocean temperatures, leads to heavier precipitation. Heavy precipitation can cause problems like flooding and landslides —where large amounts of soil or rock slide down a slope. An increase in intense precipitation comes with an increase in intense dry periods as well. Essentially, climate change causes wet places to become wetter and dry places to become drier by altering large-scale atmospheric circulation patterns. Warmer temperatures on land lead to reduced snowpack , earlier snowmelt , and evaporation of water from freshwater bodies. Extreme heat can lead to more frequent, severe, and prolonged heat waves and droughts and can make forest fires worse. On top of that, wildfires are harder to put out when air temperature is high and soil moisture is low. The number of heat waves, heavy rain events, and major hurricanes has increased in the United States. Hurricane Katrina of 2005 and Hurricane Sandy of 2012 are two of the most costly hurricanes in the history of the United States. The number of hurricanes that have occurred over recent years has not been linked to climate change, but their intensity has. The wind speed of tropical storms is increased by warmer sea-surface temperatures; by the end of the century, scientists predict maximum wind speed will increase by 2–11 percent. Coastal cities that are vulnerable to hurricanes will also be impacted by the sea level rise of around 0.3–1.2 meters (0.98–3.94 feet) in the next century, which will worsen coastal storms and flooding. Without preparing for climate change–induced environmental hazards , an increasing number of people worldwide will lose their homes and be forced into poverty. An average of around 22.5 million people have been displaced per year by climate or weather-related events since 2008. One way to prepare for extreme environmental events is by using current and past data and records to create computer models that show the frequency and intensity of these events. These models can also be used to predict when and where future events will occur and how destructive they will be. With this information, we can prepare for extreme weather events by warning people living in high-risk areas and sending disaster relief . The impact of climate change can also be observed in models by simulating the effects of different concentrations of greenhouse gases on variables, such as wind, rainfall, temperature, and air pressure. Past models used to prove that there is a relationship between climate change and extreme environmental events were not always reliable. This was due to a lack of data as well as flaws in climate models at the time. However, climate models have become more reliable, and a new field of science has developed to determine how climate change directly impacts extreme weather events: extreme event attribution. Since 2004, scientists have published more than 170 studies on the role of human-induced climate change on 190 extreme weather events. Research has found that climate change has increased the risk of wildfires in the western United States, extreme rainfall in China, and drought in South Africa. Continuous research and improvement in the field of extreme event attribution may help us figure out more precisely how climate change impacts extreme weather events–and how we might change this course.

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Climate Basics » Extreme Weather

Extreme weather and climate change.

One of the most visible consequences of a warming world is an increase in the intensity and frequency of extreme weather events. The  National Climate Assessment  finds that the number of  heat waves, heavy downpours, and major hurricanes  has increased in the United States, and the strength of these events has increased, too.

A measure of the economic impact of extreme weather is the increasing number of billion-dollar disasters, which is shown below. The map shows all types of weather disasters, some of which are known to be influenced by climate change (floods, tropical storms) and some for which a climate influence is uncertain (tornadoes).

Billion-Dollar Extreme Weather Events, 2000–2023

Click on any circle to learn about one of the billion-dollar weather events, or any state to learn about billion-dollar droughts, between January 2000 and June 2023. Source:  National Oceanic and Atmospheric Administration’s National Climatic Data Center . The Top 10 costliest events are listed at the bottom of this page, along with a description of major U.S. droughts since 2000.

NOAA calculates total, direct costs – both insured and uninsured – including physical damage to residential, commercial, and government buildings, material assets within buildings, public infrastructure, vehicles and boats, offshore energy platforms, and agricultural assets, as well as business interruption losses and disaster restoration and wildfire suppression costs. These estimates do not account for losses to natural capital, health care related costs, or values associated with loss of life.

Climate change is expected to worsen the frequency, intensity, and impacts of some types of extreme weather events. For example, sea level rise increases the impacts of coastal storms and warming can place more stress on water supplies during droughts.

That’s why many cities, state, and businesses are taking steps to  prepare for more extreme weather .

Learn more about the links between climate change and:

• Extreme Heat
• Extreme Precipitation

Data source:  NOAA, 2023 . Descriptions edited for brevity.

Data source: NOAA, 2023 . Descriptions edited for brevity.

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67% of Americans perceive a rise in extreme weather, but partisans differ over government efforts to address it

Two-thirds of Americans say extreme weather events across the country have been occurring more often than in the past. Far fewer say they’re happening about as often (28%), and only 4% say they are happening less often, according to a new Pew Research Center survey. The findings come amid reports that climate change has contributed to an increase in weather-related disasters .

Pew Research Center conducted this study to understand the public’s views of extreme weather and priorities for improving the country’s infrastructure. For this analysis, we surveyed 10,371 U.S. adults from Sept. 13 to 19, 2021. Everyone who took part in this survey is a member of the Center’s American Trends Panel (ATP), an online survey panel that is recruited through national, random sampling of residential addresses. This way nearly all U.S. adults have a chance of selection. The survey is weighted to be representative of the U.S. adult population by gender, race, ethnicity, partisan affiliation, education and other categories.  Read more about the ATP’s methodology .

Here are the questions used for the report, along with responses, and its methodology .

See also: With extreme weather events and other disasters on the rise, how well are Americans prepared?

When it comes to firsthand experiences with extreme weather, 46% of U.S. adults say the area where they live has had an extreme weather event over the past 12 months, according to the survey, which was conducted Sept. 13 to 19 among 10,371 adults.

Global leaders are set to meet this fall at COP26 , a United Nations conference on climate change, where attendees will discuss progress on cutting greenhouse gas emissions to limit global warming. Climate activists have argued that urgent action is needed as the world faces more frequent extreme weather events.

Nearly three-quarters of U.S. adults (73%) in the West South Central census division – an area hit hard by Tropical Storm Nicholas and Hurricane Ida – say they’ve experienced extreme weather within the past year. A majority of adults (59%) say the same in the Mid-Atlantic region, which was affected by recent heavy rains associated with Ida. By contrast, far fewer say they’ve experienced extreme weather in other regions over the past year, including in the South Atlantic (34%) and East North Central census divisions (31%).

In most census regional divisions, however, Democrats and Democratic-leaning independents are more likely than Republicans and Republican leaners to report experiencing extreme weather within the past year.

Overall, about half of Democrats (51%) say the area where they live has experienced extreme weather in the past year, compared with a smaller share of Republicans (39%).

A large majority of Democrats and Democratic-leaning independents (85%) say extreme weather events across the country have been occurring more often than in the past. Far fewer Republicans and GOP-leaning independents (44%) say the same; 52% of Republicans instead say such events are happening about as often as in the past.

When asked to think about the government’s role when it comes to building in areas at high risk from major storms, floods and wildfires, 62% of U.S. adults say they are more concerned that government will not go far enough in limiting new construction. A smaller share (33%) say they are more concerned government will go too far in limiting new construction in high-risk areas.

A large majority of Democrats (79%) say their greater concern is that government will not go far enough in limiting construction in areas at high risk for extreme weather.

Views among Republicans tilt in the opposite direction: 53% say they are more concerned that government will go too far in limiting new construction in high-risk areas, while 43% say their greater concern is that government will not go far enough.

Those who say they have experienced extreme weather in their community recently are slightly more likely than those who have not to say their greater concern is that government will not go far enough to limit new construction in high-risk areas, though majorities in both groups take this view (66% and 59%, respectively).  

How the public views key infrastructure goals

The survey also asked Americans about different aspects of the country’s infrastructure that the federal government could address. At the top of the list is making structural improvements to roads and bridges: Roughly six-in-ten adults (62%) say this is very important to them personally.

About half (51%) say it is very important for the federal government to build systems to make wastewater reusable in dry regions. Climate scientists expect that climate change will increase the severity of droughts in the future.

The survey also asked about the idea of stricter building standards to better withstand major storms, floods and wildfires – a strategy that could help reduce damaging effects from climate change. Around half of adults (48%) say setting stricter building standards is a very important goal to them, and 37% view this as a somewhat important goal. 

Around four-in-ten or more Americans say it is very important to them for the federal government to provide broadband internet access to communities that don’t have it (45%) and to expand public transportation systems (39%).

Only 24% of adults say it is very important for the federal government to build more charging stations to increase the use of electric vehicles receives – the lowest level of public importance for any of the six items in the survey. Around four-in-ten adults (41%) say this is not important, while about a third (34%) say it is somewhat important to them. In an earlier Center survey , just 7% of U.S. adults said they currently own an electric or hybrid vehicle.

Overall, 51% of the public favors the infrastructure bill now being debated in Congress, compared with a smaller share (20%) who oppose it; 29% say they aren’t sure how they feel about it.

Partisanship matters far more than other factors – including where people live – when it comes to Americans’ views about the country’s infrastructure and the government’s role in adaptation to risks from extreme weather.

For instance, 62% of Democrats say it’s a very important goal for the federal government to set stricter standards to better withstand major storms, floods and wildfires. Half as many Republicans (31%) say that is very important to them personally.

There are generally modest differences in views between those who say they have experienced extreme weather locally in the past year and those who say they have not.

Note: Here are the questions used for the report, along with responses, and its methodology .

• Climate, Energy & Environment
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Cary Funk is director of science and society research at Pew Research Center .

Alec Tyson is an associate director of research at Pew Research Center .

Majority of Americans support more nuclear power in the country

Americans’ extreme weather policy views and personal experiences, u.s. adults under 30 have different foreign policy priorities than older adults, about 3 in 10 americans would seriously consider buying an electric vehicle, how americans view national, local and personal energy choices, most popular.

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Extreme Weather: Interconnections in Extreme Weather

Discover the ways in which air and water interact in a vast complex system. This video clip illustrates the interconnections between rising sea levels, forest fires, droughts, heat waves, typhoons, powerful storms, and flooding.

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- [Narrator] Average global temperatures have risen one and a half degrees Fahrenheit in the last 150 years. A seemingly small change with a far reaching impact. For some regions, it means heavier snowfall. For others, longer droughts. Our air and water interact in a vast, complex system. Drought creates conditions for more forest fires. Melting glaciers contribute to sea levels rising. Powerful storms can bring widespread flooding. In the last decade, more than 150 million people lost their homes to extreme weather events.

Fires, heatwaves, typhoons, tornadoes, flooding. Everything is connected and the race is on to better understand the dynamics of our planet's natural forces.

Transcripción (Español)

- [Narrador] Las temperaturas globales promedio han aumentado un grado en los últimos 150 años. Un cambio pequeño con un impacto de largo alcance. Para algunas regiones, significa más nevadas. Para otras, sequías más largas. El aire y agua interactúan en un vasto y complejo sistema. La sequía aumenta el riesgo de incendios forestales. Los glaciares que se derriten contribuyen a que suba el nivel del mar. Fuertes tormentas pueden provocar grandes inundaciones. En la última década, más de 150 millones de personas han perdido sus hogares por eventos climáticos extremos.

Incendios, olas de calor, tifones, tornados, inundaciones. Todo está conectado y pronto debemos entender mejor la dinámica de las fuerzas naturales de nuestro planeta.

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What is global warming?

What causes global warming, how is global warming linked to extreme weather, what are the other effects of global warming, where does the united states stand in terms of global-warming contributors, is the united states doing anything to prevent global warming, is global warming too big a problem for me to help tackle.

A: Since the Industrial Revolution, the global annual temperature has increased in total by a little more than 1 degree Celsius, or about 2 degrees Fahrenheit. Between 1880—the year that accurate recordkeeping began—and 1980, it rose on average by 0.07 degrees Celsius (0.13 degrees Fahrenheit) every 10 years. Since 1981, however, the rate of increase has more than doubled: For the last 40 years, we’ve seen the global annual temperature rise by 0.18 degrees Celsius, or 0.32 degrees Fahrenheit, per decade.

The result? A planet that has never been hotter . Nine of the 10 warmest years since 1880 have occurred since 2005—and the 5 warmest years on record have all occurred since 2015. Climate change deniers have argued that there has been a “pause” or a “slowdown” in rising global temperatures, but numerous studies, including a 2018 paper published in the journal Environmental Research Letters , have disproved this claim. The impacts of global warming are already harming people around the world.

Now climate scientists have concluded that we must limit global warming to 1.5 degrees Celsius by 2040 if we are to avoid a future in which everyday life around the world is marked by its worst, most devastating effects: the extreme droughts, wildfires, floods, tropical storms, and other disasters that we refer to collectively as climate change . These effects are felt by all people in one way or another but are experienced most acutely by the underprivileged, the economically marginalized, and people of color, for whom climate change is often a key driver of poverty, displacement, hunger, and social unrest.

A: Global warming occurs when carbon dioxide (CO 2 ) and other air pollutants collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth’s surface. Normally this radiation would escape into space, but these pollutants, which can last for years to centuries in the atmosphere, trap the heat and cause the planet to get hotter. These heat-trapping pollutants—specifically carbon dioxide, methane, nitrous oxide, water vapor, and synthetic fluorinated gases—are known as greenhouse gases, and their impact is called the greenhouse effect.

Though natural cycles and fluctuations have caused the earth’s climate to change several times over the last 800,000 years, our current era of global warming is directly attributable to human activity—specifically to our burning of fossil fuels such as coal, oil, gasoline, and natural gas, which results in the greenhouse effect. In the United States, the largest source of greenhouse gases is transportation (29 percent), followed closely by electricity production (28 percent) and industrial activity (22 percent). Learn about the natural and human causes of climate change .

Curbing dangerous climate change requires very deep cuts in emissions, as well as the use of alternatives to fossil fuels worldwide. The good news is that countries around the globe have formally committed—as part of the 2015 Paris Climate Agreement —to lower their emissions by setting new standards and crafting new policies to meet or even exceed those standards. The not-so-good news is that we’re not working fast enough. To avoid the worst impacts of climate change, scientists tell us that we need to reduce global carbon emissions by as much as 40 percent by 2030. For that to happen, the global community must take immediate, concrete steps: to decarbonize electricity generation by equitably transitioning from fossil fuel–based production to renewable energy sources like wind and solar; to electrify our cars and trucks; and to maximize energy efficiency in our buildings, appliances, and industries.

A: Scientists agree that the earth’s rising temperatures are fueling longer and hotter heat waves , more frequent droughts , heavier rainfall , and more powerful hurricanes .

In 2015, for example, scientists concluded that a lengthy drought in California—the state’s worst water shortage in 1,200 years —had been intensified by 15 to 20 percent by global warming. They also said the odds of similar droughts happening in the future had roughly doubled over the past century. And in 2016, the National Academies of Science, Engineering, and Medicine announced that we can now confidently attribute some extreme weather events, like heat waves, droughts, and heavy precipitation, directly to climate change.

The earth’s ocean temperatures are getting warmer, too—which means that tropical storms can pick up more energy. In other words, global warming has the ability to turn a category 3 storm into a more dangerous category 4 storm. In fact, scientists have found that the frequency of North Atlantic hurricanes has increased since the early 1980s, as has the number of storms that reach categories 4 and 5. The 2020 Atlantic hurricane season included a record-breaking 30 tropical storms, 6 major hurricanes, and 13 hurricanes altogether. With increased intensity come increased damage and death. The United States saw an unprecedented 22 weather and climate disasters that caused at least a billion dollars’ worth of damage in 2020, but, according to NOAA, 2017 was the costliest on record and among the deadliest as well: Taken together, that year's tropical storms (including Hurricanes Harvey, Irma, and Maria) caused nearly $300 billion in damage and led to more than 3,300 fatalities.

The impacts of global warming are being felt everywhere. Extreme heat waves have caused tens of thousands of deaths around the world in recent years. And in an alarming sign of events to come, Antarctica has lost nearly four trillion metric tons of ice since the 1990s. The rate of loss could speed up if we keep burning fossil fuels at our current pace, some experts say, causing sea levels to rise several meters in the next 50 to 150 years and wreaking havoc on coastal communities worldwide.

A: Each year scientists learn more about the consequences of global warming , and each year we also gain new evidence of its devastating impact on people and the planet. As the heat waves, droughts, and floods associated with climate change become more frequent and more intense, communities suffer and death tolls rise. If we’re unable to reduce our emissions, scientists believe that climate change could lead to the deaths of more than 250,000 people around the globe every year and force 100 million people into poverty by 2030.

Global warming is already taking a toll on the United States. And if we aren’t able to get a handle on our emissions, here’s just a smattering of what we can look forward to:

• Disappearing glaciers, early snowmelt, and severe droughts will cause more dramatic water shortages and continue to increase the risk of wildfires in the American West.
• Rising sea levels will lead to even more coastal flooding on the Eastern Seaboard, especially in Florida, and in other areas such as the Gulf of Mexico.
• Forests, farms, and cities will face troublesome new pests , heat waves, heavy downpours, and increased flooding . All of these can damage or destroy agriculture and fisheries.
• Disruption of habitats such as coral reefs and alpine meadows could drive many plant and animal species to extinction.
• Allergies, asthma, and infectious disease outbreaks will become more common due to increased growth of pollen-producing ragweed , higher levels of air pollution , and the spread of conditions favorable to pathogens and mosquitoes.

Though everyone is affected by climate change, not everyone is affected equally. Indigenous people, people of color, and the economically marginalized are typically hit the hardest. Inequities built into our housing , health care , and labor systems make these communities more vulnerable to the worst impacts of climate change—even though these same communities have done the least to contribute to it.

A: In recent years, China has taken the lead in global-warming pollution , producing about 26 percent of all CO2 emissions. The United States comes in second. Despite making up just 4 percent of the world’s population, our nation produces a sobering 13 percent of all global CO2 emissions—nearly as much as the European Union and India (third and fourth place) combined. And America is still number one, by far, in cumulative emissions over the past 150 years. As a top contributor to global warming, the United States has an obligation to help propel the world to a cleaner, safer, and more equitable future. Our responsibility matters to other countries, and it should matter to us, too.

A: We’ve started. But in order to avoid the worsening effects of climate change, we need to do a lot more—together with other countries—to reduce our dependence on fossil fuels and transition to clean energy sources.

Under the administration of President Donald Trump (a man who falsely referred to global warming as a “hoax”), the United States withdrew from the Paris Climate Agreement, rolled back or eliminated dozens of clean air protections, and opened up federally managed lands, including culturally sacred national monuments, to fossil fuel development. Although President Biden has pledged to get the country back on track, years of inaction during and before the Trump administration—and our increased understanding of global warming’s serious impacts—mean we must accelerate our efforts to reduce greenhouse gas emissions.

Despite the lack of cooperation from the Trump administration, local and state governments made great strides during this period through efforts like the American Cities Climate Challenge and ongoing collaborations like the Regional Greenhouse Gas Initiative . Meanwhile, industry and business leaders have been working with the public sector, creating and adopting new clean-energy technologies and increasing energy efficiency in buildings, appliances, and industrial processes. 

Today the American automotive industry is finding new ways to produce cars and trucks that are more fuel efficient and is committing itself to putting more and more zero-emission electric vehicles on the road. Developers, cities, and community advocates are coming together to make sure that new affordable housing is built with efficiency in mind , reducing energy consumption and lowering electric and heating bills for residents. And renewable energy continues to surge as the costs associated with its production and distribution keep falling. In 2020 renewable energy sources such as wind and solar provided more electricity than coal for the very first time in U.S. history.

President Biden has made action on global warming a high priority. On his first day in office, he recommitted the United States to the Paris Climate Agreement, sending the world community a strong signal that we were determined to join other nations in cutting our carbon pollution to support the shared goal of preventing the average global temperature from rising more than 1.5 degrees Celsius above preindustrial levels. (Scientists say we must stay below a 2-degree increase to avoid catastrophic climate impacts.) And significantly, the president has assembled a climate team of experts and advocates who have been tasked with pursuing action both abroad and at home while furthering the cause of environmental justice and investing in nature-based solutions.

A: No! While we can’t win the fight without large-scale government action at the national level , we also can’t do it without the help of individuals who are willing to use their voices, hold government and industry leaders to account, and make changes in their daily habits.

Wondering how you can be a part of the fight against global warming? Reduce your own carbon footprint by taking a few easy steps: Make conserving energy a part of your daily routine and your decisions as a consumer. When you shop for new appliances like refrigerators, washers, and dryers, look for products with the government’s ENERGY STAR ® label; they meet a higher standard for energy efficiency than the minimum federal requirements. When you buy a car, look for one with the highest gas mileage and lowest emissions. You can also reduce your emissions by taking public transportation or carpooling when possible.

And while new federal and state standards are a step in the right direction, much more needs to be done. Voice your support of climate-friendly and climate change preparedness policies, and tell your representatives that equitably transitioning from dirty fossil fuels to clean power should be a top priority—because it’s vital to building healthy, more secure communities.

You don’t have to go it alone, either. Movements across the country are showing how climate action can build community , be led by those on the front lines of its impacts, and create a future that’s equitable and just for all .

This story was originally published on March 11, 2016 and has been updated with new information and links.

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How Have You Experienced Extreme Weather?

This summer brought record heat, floods, droughts and wildfires. Tell us how the mounting consequences of climate change have affected you.

By Callie Holtermann

It was “ a summer of disasters .”

As the planet warms, extreme weather events such as wildfires, heat waves, hurricanes, droughts and floods are becoming more common. What extreme weather did you hear about during the summer? Did you experience any yourself?

How do you feel about the dangerous weather occurring around the world? What do these events tell you about where we are in the fight against climate change — and how we should move forward?

In “ Overlapping Disasters Expose Harsh Climate Reality: The U.S. Is Not Ready ,” Christopher Flavelle, Anne Barnard, Brad Plumer and Michael Kimmelman write:

In Louisiana and Mississippi, nearly one million people lack electricity and drinking water after a hurricane obliterated power lines. In California, wildfire menaces Lake Tahoe, forcing tens of thousands to flee. In Tennessee, flash floods killed at least 20; hundreds more perished in a heat wave in the Northwest. And in New York City, 7 inches of rain fell in just hours Wednesday, drowning people in their basements. Disasters cascading across the country this summer have exposed a harsh reality: The United States is not ready for the extreme weather that is now becoming frequent as a result of a warming planet. “These events tell us we’re not prepared,” said Alice Hill, who oversaw planning for climate risks on the National Security Council during the Obama administration. “We have built our cities, our communities, to a climate that no longer exists.” In remarks Thursday, President Biden acknowledged the challenge ahead. “And to the country, the past few days of Hurricane Ida and the wildfires in the West and the unprecedented flash floods in New York and New Jersey is yet another reminder that these extreme storms and the climate crisis are here,” said Mr. Biden, who noted that a $1 trillion infrastructure bill pending in Congress includes some money to gird communities against disasters. “We need to do — be better prepared. We need to act.”

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• Perspective
• Published: 15 June 2020

Understanding and managing connected extreme events

• Colin Raymond   ORCID: orcid.org/0000-0003-3093-5774 1 , 2 ,
• Radley M. Horton   ORCID: orcid.org/0000-0002-5574-9962 3 ,
• Jakob Zscheischler   ORCID: orcid.org/0000-0001-6045-1629 4 , 5 ,
• Olivia Martius 4 , 6 ,
• Amir AghaKouchak   ORCID: orcid.org/0000-0003-4689-8357 7 , 8 ,
• Jennifer Balch 9 , 10 ,
• Steven G. Bowen 11 ,
• Suzana J. Camargo   ORCID: orcid.org/0000-0002-0802-5160 3 ,
• Jeremy Hess 12 , 13 ,
• Kai Kornhuber   ORCID: orcid.org/0000-0001-5466-2059 3 , 14 ,
• Michael Oppenheimer   ORCID: orcid.org/0000-0002-9708-5914 15 , 16 ,
• Alex C. Ruane   ORCID: orcid.org/0000-0002-5582-9217 17 ,
• Thomas Wahl 18 , 19 &
• Kathleen White 20  

Nature Climate Change volume  10 ,  pages 611–621 ( 2020 ) Cite this article

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This article has been updated

Extreme weather and climate events and their impacts can occur in complex combinations, an interaction shaped by physical drivers and societal forces. In these situations, governance, markets and other decision-making structures—together with population exposure and vulnerability—create nonphysical interconnections among events by linking their impacts, to positive or negative effect. Various anthropogenic actions can also directly affect the severity of events, further complicating these feedback loops. Such relationships are rarely characterized or considered in physical-sciences-based research contexts. Here, we present a multidisciplinary argument for the concept of connected extreme events, and we suggest vantage points and approaches for producing climate information useful in guiding decisions about them.

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In 2017, a parade of severe tropical cyclones devastated the eastern Caribbean, with damages to property and infrastructure that were exacerbated by the consecutive storms 1 , 2 and by the depleted response ability of the U.S. Federal Emergency Management Agency stemming from Hurricane Harvey several weeks earlier 3 . A humanitarian crisis ensued in which, predictably, the populations with the highest baseline vulnerability tended to suffer most 4 . In 2018, an exceptionally cold and wet early spring affected winter-cereal harvests and hindered spring planting across Europe, and this, compounded with a hot and dry summer, led to agricultural losses in consecutive cropping seasons—raising wheat and barley prices in the integrated European Union market by 30% and straining the continent’s government and insurance budgets 5 , 6 .

We term such combinations of extreme events ‘connected’, to convey the diversity and complexity of interacting physical and societal mechanisms that cause their impacts to be amplified relative to the impacts from those same events occurring separately or univariately (Table 1 ). Note that this definition includes hazards which result in impacts only or primarily via feedback loops involving anthropogenic systems of some kind. Here, we use ‘impacts’ to mean the losses arising from the interaction of hazard, vulnerability and exposure (synonymous with consequences or outcomes), and ‘risk’ to mean potential or unrealized losses, both as defined by the IPCC 7 . Where such a distinction is not necessary, we use ‘impacts’ as a general term encompassing both concepts.

As further elaborated in Box 1 , ‘connection’ incorporates and builds on the physical-hazard-based framework of ‘compound’ weather and climate events 8 , 9 , 10 , 11 , 12 ; ‘interacting’, ‘cascading’ or ‘multi-risk’ natural hazards 13 , 14 , 15 , 16 , 17 , 18 ; and systemic risks and complexity science 19 . Our discussion is closely informed by advances and assessments in these fields, but homes in on attributes unique to extreme weather and climate events as well as on the exacerbating role that anthropogenic actions can play with regards to both their severity and impacts.

In this Perspective, we describe the broad applicability of the concept of connected extremes and how relevant expertise, disciplinary knowledge and insights inside and outside of academia can best be solicited and employed so applied-science teams that include climate scientists focus on the variables, metrics, locations and temporal aspects of greatest societal importance. We reflect on connected extremes through our research and practitioner experiences in the sectors of food, water, human health, infrastructure and insurance, and show how current risk-management approaches fall short in addressing the complex challenges associated with connected extremes. We then present specific recommendations for how collaborations among the research and decision-making communities may be expanded and enhanced. Consequently, we also aim to inform policies toward the adaptation and mitigation strategies most appropriate for reducing risks from and increasing resilience to connected extremes, which may differ from those designed for single extremes.

Box 1 Connected extremes definition and conceptual framework

Defining connected extreme weather and climate events

Compound weather and climate events are comprised of multiple distinguishable physical drivers and/or hazards and their risks. These can be subdivided according to the primary means of interaction: temporal compounding (for example, a sequence of storms), spatial compounding (for example, synchronous crop failures), preconditioning (for example, rain-on-snow flooding) and concurrence of multiple variables (for example, storm surge, pluvial flooding and high winds from a single storm). Details on these categories can be found in ref. 8 .

The concept of connected extreme weather and climate events further recognizes that compound event impacts are often substantially and nonlinearly influenced by non-physical factors such as exposure and vulnerability, cutting across sectors and scales (from personal to society wide). These ‘societal mechanisms’ can tie together the impacts from two or more climate extremes, whether due to resource constraints (for example, exhaustion of an insurance fund or pool of emergency responders), health considerations (for example, power outages or medication-supply-chain disruptions) or other linkages (Fig. 1 ). Other possible longer-term feedbacks range from changes in risk pricing to wholesale rethinking of risk-management strategies 30 , which in Fig. 1 are compressed into the ‘Response’ category. Whatever their nature, connections’ meaningfulness lies in their robustness and traceability, terms which can best be defined by the stakeholders involved.

It is the creation or strengthening of the connections between events, in the impacts space and involving anthropogenic systems, that leads to our terminology of ‘connected’ events as being distinct from ‘compound’ events, and also from interacting-risk or multi-risk frameworks that focus on combinations of physical hazards 13 .

A challenge of ‘spaces’

One framework for understanding the research and decision-making issues associated with connected extremes is to view them as resulting from a mismatch between the planning and response decisions that would be achieved by conventional methods (the ‘decision space’) and those that would optimally address the full set of physical possibilities (the ‘event space’) (Fig. 3 ). Many organizations are constrained to make decisions within a narrow spatiotemporal domain, leading to conflicting decisions at one scale versus another. A small city with a limited budget (represented by Actor 1 in Fig. 3 ) or a government agency with a specific mission cannot be expected to have the capacity to coordinate across multiple spatial scales to optimally plan for or respond to multivariate or sequential connected extremes which fall only partially under its purview, much less spatially compounding extremes like river flooding caused by conditions upstream. Additionally, physical processes and data availability make the event space difficult to reliably estimate—a confounding uncertainty when trying to reach a decision under political, financial and technical constraints 95 , 112 , 113 .

Major wildfires, for instance, are often ‘connected’ in several ways 97 . Actors such as city departments, national agencies, private landowners, insurers, corporations and non-profits must decide how to manage long-term fire risk, emergency responses and recovery, including decisions about how and where to reinvest. Each of these spheres of action is guided by (1) the size and mandate of the decision makers, which defines their mission and hence affects their quantity of resources; (2) their ability and/or incentive to distribute risk; and (3) the political expectations or regulatory requirements under which they operate. These diverse incentives and restrictions complicate efforts to plan and execute a holistic response that does not, for example, merely delay the risk or transfer it to other sectors 95 . Hence, understanding this patchwork of ‘decision spaces’ can aid in characterizing the type of decision-relevant knowledge that research on connected extremes should aim to generate. Social scientists, risk managers and boundary-spanning organizations are indispensable here, by helping to build and leverage communication networks that can delineate the feasible intersection of the decision and event spaces.

Physical basis, societal relevance

Connection between climate extremes can be conceived of as complex time- and space-varying physical and societal mechanisms that relate one event to another (Fig. 1 ), ultimately causing major impacts (Fig. 2 and Box 1 ). In the case mentioned in the opening paragraph, a connection was created between the impacts of Hurricanes Harvey and Maria, severe but otherwise unrelated events that occurred 3,300 km and 26 days apart 3 . Focusing on Hurricane Maria’s impacts in Puerto Rico—which included more than 3,000 deaths and nearly US$100 billion in damage—post-event reports identified the island’s under-maintained infrastructure, limited budget, aging population and territory status as among the factors which contributed to its vulnerability 3 , 4 , 20 , 21 . While the hazards of heavy precipitation and strong winds caused large amounts of direct damage, such as road washouts and drownings, the impacts were exacerbated by slow and patchy relief and recovery efforts. Emergency response systems had been stretched thin by Hurricane Harvey striking Texas the previous month and Hurricane Irma striking Florida the previous week, with administrative mismanagement also coming into play 1 , 4 , 21 , 22 , 23 . As summarized by the U.S. Federal Emergency Management Agency (FEMA), “FEMA not only exhausted commodities on hand but also exhausted pre-negotiated contracts to provide meals, tarps, water and other resources during the responses to Hurricanes Harvey and Irma. Therefore, the concurrent response for Hurricane Maria required FEMA to rapidly solicit vendors… increased contract demands from the hurricane season severely taxed FEMA’s acquisitions process and contracting personnel…” 3 . Across Puerto Rico, mortality was highest in isolated municipalities and those with low socioeconomic development, highlighting linkages between vulnerability and impacts 21 , 24 . The quality and equity of the rebuilt physical systems, reimagined social-support networks and revised decision-making structures will be reflected in future exposure and vulnerability, and most tangibly in the impacts when combinations of extreme events occur again 23 , 25 .

a , Generalized diagram of the interactions among physical and societal drivers that constitute connected extreme events. Boxes 2 and 3 together represent ‘risk’, as defined in the text. b , An illustration of a for the case of Hurricane Maria impacting Puerto Rico in 2017 following a sequence of severe tropical cyclones in the Caribbean and Gulf of Mexico. For simplicity, only one or two examples in each category are presented. Box 1 highlights behaviours 110 , territory status 20 , building codes 4 , grid upkeep 4 , government budgets 3 and communications systems 4 . Box 2 highlights isolated mountain towns 21 and the aging power system 20 . Box 3 highlights Hurricanes Maria 1 and Harvey 111 . TX, Texas. Box 4 highlights flooding and treefall 21 . Box 5 highlights mortality 21 and infrastructure damage 4 . Box 6 highlights rebuilding of infrastructure 20 and policy changes 4 . Arrows indicate FEMA mismanagement 22 , rebuilt drainage systems 25 , future extreme-precipitation increases 111 , location and quality of rebuilt systems 4 , personnel, supplies and information 23 .

Lines trace the annual global sum of estimated economic losses caused by tropical cyclones (green), floods (blue), droughts (orange) and wildfires (red). Annotations indicate the largest events in high-loss years followed by several of the (first row) physical and (second row) societal drivers that shaped the total impacts. Economic-loss data are from Aon, Catastrophe Insight Division.

Generalized diagram of the spatiotemporal scales associated with connected extremes (across both physical and societal aspects) compared against the typical spatiotemporal scales of the decision-making that affects the societal response to them, for two example events and two example actors. The meters for each actor indicate their (hypothetical) relative characteristics in terms of technical capability (T), cultural or political capital (K) and financial or geographic size (S). High meter readings correspond to a capacity for broad, complex, long-term and expensive actions, whereas low meter readings correspond to a necessity for taking localized, simpler, short-term and less-expensive actions.

We argue that these types of complexities mean that successfully parsing, preparing for and responding to connected extreme events requires deep collaboration across sectors and disciplines. Physical hazards, for instance, are shaped by timing, location and meteorological context, while political, financial, infrastructural and cultural networks make certain combinations of events especially potent from an impacts standpoint, through their exposure and vulnerability characteristics. These networks include traits strongly dependent on governance, culture, historical precedent, information flow and other legacies—‘societal mechanisms’ that are ever-changing and that can create systemic risks when interconnections result in fragility rather than resilience 19 , 26 , 27 , due to internal dynamics or external influences such as climate change.

In this context of intrinsic interdisciplinarity, shifting relationships and capacity for surprise (such as the crossing of tipping points) 28 , joint physical–societal assessments are critically important for building scientific understanding and improving risk management in response to connected extremes. Moreover, adaptation strategies are ever-evolving under a changing climate 29 , requiring iterative efforts to evaluate their efficacy 30 . Not only must risks be identified, monitored and evaluated, but the risk-management process itself must be subject to reframing and transformation to match the risks (or state of knowledge of them). Greater severity and frequency of many hazards as a result of climate change, combined with a lower loss threshold in populations with higher vulnerability, makes such efforts especially urgent.

Societal impacts of connected extremes in five major sectors

In this section, we provide examples of concepts and methods regarding connected extremes through the lens of five sectors reflecting our research and practitioner expertise: food, water, human health, infrastructure and insurance. We discuss (1) how each sector is affected, (2) current responses and their effectiveness and (3) important types of knowledge that new decision-relevant collaborations could produce.

The agricultural sector consists of a multitude of heterogeneous farming systems and complex networks of food supply, demand and trade that exhibit high systemic risk 31 . In this context, connected extremes can threaten regional and global food security.

Crops are particularly vulnerable to multivariate hot and dry events that cause water stress, while workers and livestock are burdened by hot and humid extremes that cause physiological stress 32 , 33 . The sequence in which extremes occur can exacerbate overall impacts, given crop physiologies and the need for particular field conditions during key developmental stages 34 . Early-season floods can delay field preparation and planting, pushing back crop calendars in a manner that exposes crops to late-season frost or drought stress. Early wet conditions may also weaken plants’ ability to cope with subsequent extremes by limiting their root depths or creating conditions favourable for pest infestations. Alternatively, early-season drought can cause farmers to deplete water resources and thus increase vulnerability to dry spells later in the season.

Currently, some crop models analyse water, nitrogen and heat stress on each day and apply only the largest stress factor, missing the compound nature of many hazards. Conditional effects are also challenging for statistical crop-model yield projections, which, for maximal accuracy, would require incorporation of the timing of extreme events as well as of cross-terms that identify sequential connections between early- and late-season extremes of different variable types 35 .

The confluence of all these issues is crystallized in considering the prospect of a multiple-breadbasket failure, with extreme events striking two or more important agricultural production zones, resulting in a large aggregate effect on global food production and prices 36 , 37 . Such a situation could result from independent regional extremes randomly co-occurring, or could have a correlation structure driven by teleconnections linked to major modes of climate variability 38 , 39 . Recent decades have seen a consolidation of global production into fewer regions and a proliferation of monoculture systems, increasing the potential for a small number of synchronous regional-scale extremes to have widespread impacts 40 . Agricultural trade models connect regional production into wider balances of supply and demand to achieve long-term equilibria; however, year-by-year actions of stakeholders along the value chains from field to global market and from global market to supermarket shelf are not as well-simulated, hindering resilience planning to ‘shocks’ such as those that connected extremes can induce.

To prevent food system shocks, there is a great need for enhanced understanding of the impacts of specific sequences of extreme events at a local scale, particularly if risks could be identified early enough to allow for appropriate farming and trading countermeasures. Complementarily, connections between extremes in the food context often manifest through non-farm elements such as transport and processing, so incorporating this systems knowledge when designing climate research—even if only as an initial consideration—would significantly improve its usefulness.

Access to clean water in sufficient quantities is a fundamental requirement for human societies. In a growing and urbanizing world, water management and distribution are challenging but unavoidable tasks, especially when both critical water states—flood and drought—can result from a combination of physical drivers and can be exacerbated by correlations among them 41 , 42 .

Compounding effects can alter flood risk in several distinct ways. Antecedent conditions, such as groundwater or soil moisture, often play a key role in flood generation 10 . Concurrent flood drivers can be of the same type, such as discharge at river confluences 43 , or different types, such as the superposition of high tides, storm surges, waves and freshwater inflow leading to extreme total water levels along coastlines 44 , 45 . Both spatial and temporal compounding play into the severity and impacts of high- and low-water events and, consequently, the outcomes of hydrological risk assessments 46 , 47 . Analogously, droughts are inherently multivariate phenomena that respond nonlinearly to changes in controlling parameters, such as temperature, precipitation and soil moisture 48 , 49 , 50 . Furthermore, drought impacts are often largest when they compound temporally and spatially, termed ‘mega-droughts’ 51 , and it is these situations when interactions with other hazards such as heat waves are strongest 52 .

The problem of interconnected hydrological drivers has prompted many advances in statistical methods for compound events, including copulas and scenario modelling (Table 2 ) 15 , 53 . One insight these have revealed is that, for droughts as well as floods, changes in the correlation structure between drivers can alone lead to large changes in extreme events 54 , 55 . Acting on this awareness, agencies such as the U.S. Army Corps of Engineers have begun accounting for correlations between river discharge and storm surge when planning coastal projects. The Corps is also assessing the effects of sequential droughts and floods on reservoir operations, and of post-fire precipitation on reservoir sedimentation.

Anthropogenic systems interact with the natural environment to direct and shape the ultimate impacts of extreme hydrological events. For example, urban drainage systems modulate both the amount of surface flooding and the water quality at discharge points, due to the correlation of combined sewer overflows with heavy precipitation. In exceptional droughts, reservoirs used primarily for water supply, flood mitigation or power generation may actually worsen water shortages and thereby tensions between different regions or water users 56 . These physical–societal dynamics lead to uncertainties in water scarcity projections even larger than the corresponding uncertainties in precipitation 57 . Actions taken during an event can often represent an additional layer. During the spring 2011 Mississippi River floods driven by heavy rain and snowmelt across the U.S. Upper Midwest, multiple spillways were opened (as designed) to protect downstream urban areas, resulting in some flooding of agricultural lands 58 . Similarly, storm-surge barriers prevent ocean-side flooding when closed but can worsen wave impacts on the seaward side while simultaneously causing freshwater to accumulate on the landward side, affecting areas that might not otherwise have been at risk, especially when rainfall-driven river discharge is also high 59 .

For both types of hydrological extremes, decisions made throughout a region have physical and behavioural consequences which tend to accumulate over time and then prominently manifest when water becomes scarce or overabundant. The need to better understand and account for the joint distribution of physical drivers and societal mechanisms warrants close collaboration between social scientists, engineers, hydrologists, climate scientists and water agencies—encapsulated by the relatively new field of socio-hydrology 60 .

Population health is a function of a wide set of determinants, including interactions with multiple environmental factors over time 61 . Where, when and which populations are exposed to connected extremes are all strong predictors of the severity of impacts 62 . Additionally, demographic vulnerability is itself often multivariate and temporally compounding 63 . For these reasons, an integrated health perspective—considering wealth, insurance, housing, food security and other essentials—is gaining traction among researchers and practitioners. This evolution makes the connected extremes framework a natural one.

In the healthcare context, important types of compounding include multivariate extremes—including heat-and-humidity as well as heat-and-air-quality events 33 , 64 —and temporal compounding, on timescales ranging from hourly-to-daily (for emergency response) to subseasonal-to-seasonal (for preventative campaigns, supply-chain planning and recovery efforts). For extreme heat, diverse health hazards will very likely interact more frequently as the recovery time between heat waves shrinks, making it a prototypical instance of a connection between extreme events enhanced by climate change 65 . Other societal drivers such as power outages, whether resulting directly from physical drivers 66 or induced to prevent poorly maintained equipment from sparking wildfires during compound wind and low-humidity events (such as in the 2019 California fire season), can also feed back onto health outcomes. These examples underscore how human decisions made over decades modulate the health impacts of extreme events on much shorter timescales.

Both knowledge and capacity for action pose challenges with regards to the impacts of connected extreme events on the health sector. Many epidemiological analyses take limited advantage of sophisticated methods for modelling these types of complex risks. Additionally, from the operational point of view inherent to healthcare delivery, the motivation to adopt new tools and methods—and to follow through on the ensuing recommendations—can be low in the face of everyday demands, a lack of dedicated personnel, limited utilization of system modelling and difficulties with funding for structural change. Health systems are diversely organized around the world, with varying but typically limited coordination, information sharing and inter-sector collaboration 67 . Although enhanced integration of disaster risk reduction, disaster preparedness and disaster response has the potential to manage risk more effectively, these activities remain somewhat tenuously linked, with the result that the health sector is sometimes overwhelmed by the impacts of connected extremes such as Superstorm Sandy (which was followed by a cold Nor’easter) or Hurricane Maria. In these cases, personnel are not efficiently deployed, supply chains are disrupted and suboptimal health outcomes are achieved. Such crises have also spurred improvements in organization and communications 68 , 69 .

This situation creates an outsize need for improved quantification of and communication about connected extremes with major potential health impacts, coordinated to align with and inform specific procedural choices. For instance, while there have been some efforts to systematically examine how connected extreme events may impact health systems 70 , much more could be done to determine where and how connected extremes may result in unanticipated impacts, such as by drawing on past experiences 71 . The health sector could benefit from examples of how other sectors have anticipated impacts and incorporated this learning into reforms.

Infrastructure

Critical infrastructure includes systems that provide energy, water, food, transport and security. Connected extremes can exert forces on these systems beyond their design specifications, making it imperative to understand and incorporate such effects into infrastructure planning and risk assessments. The relevant interactions are typically poorly constrained, despite the large investments involved, due to the great complexities of the systems and the numerous and widely disparate actors with jurisdiction over them.

Large wildfires and tropical cyclones—themselves sometimes compound events—frequently cause flooding, slope failures and vegetation blowdown which, in combination with vulnerable infrastructure, can impede emergency response efforts and post-disaster rebuilding 4 , 72 . Such situations may also create unanticipated additional hazards, such as major traffic jams 73 . Well-designed infrastructure can exhibit strategic purposeful failures which nonetheless result in property damage or loss of life, as in the Mississippi River flood example discussed above. Emergency response and rebuilding efforts may be particularly vulnerable to sequences of extremes, such as a heat wave following a hurricane- 66 or wildfire-induced power outage.

Infrastructure decisions (investment, maintenance and outreach) play a key role in connecting extremes, especially for the most exposed or vulnerable communities. During the Thailand floods of 2011, politically motivated decisions on how to route water resulted in the protection of central Bangkok at the expense of peripheral areas, where major manufacturing facilities were located 74 . The resulting floods caused large economic losses in Thailand and globally due to supply-chain disruption that played out over the following months. At the dry end of the spectrum, the pre-emptive California power outages mentioned above were deemed necessary due to overgrown vegetation and aging equipment in addition to severe fire weather.

As a result, there is increasing adoption of systems thinking for infrastructure 3 , 4 —considering each subsystem’s design, management and interconnections—but this requires climate information of sufficient detail and reliability to be optimally employed. The interactions described here highlight the necessity for more collaboration at the interface between natural sciences, engineering and social sciences to enable policy choices that are well-informed, robust and equitable over the typically long lifetime of an infrastructure project.

Insurance plays an integral role in risk management and disaster recovery for diverse sectors and at scales ranging from personal to global. However, emerging spatial correlations across multiple hazards of the same or different type could, if unrecognized, pose a systemic risk to (re)insurers and the broader economy.

Humanitarian and property impacts from large-scale disasters with multiple drivers (for example, heat and drought leading to wildfires) or multivariate hazards (for example, wind and water for tropical cyclones, or wind, hail and water for severe convective storms) can be extremely costly (Fig. 2 ). The earlier examples of Hurricanes Harvey and Maria in 2017, and the simultaneous California wildfires in 2017 and again in 2019, are illustrative. The complexities associated with recognizing and responding to such perils are amplified when the regions affected are underinsured and/or repeatedly exposed 75 , 76 , 77 . Additionally, the global ‘protection gap’—the portion of the economic cost of disasters not covered by insurance—is still a concern for increasingly at-risk regions within Latin America, Africa and Asia 78 . Health insurance coverage, likewise, is strongly correlated with sociodemographic factors, creating another source of inequality and population vulnerability.

The catastrophe models commonly used in the insurance industry are limited in their ability to see connected multihazard events ‘over the horizon’ because they are calibrated using observed or synthetically generated event sets and portfolio exposures. Event types that are known to be possible but considered highly unlikely (called ‘grey swans’) are not well-captured in this framework, precluding proper risk quantification. Even when connected extremes are able to be represented, interpreting and acting on this knowledge remains challenging for (re)insurers.

The overall risks associated with large, volatile, multivariate extreme-event impacts make it essential for (re)insurers and businesses to make decisions based on an accurate evaluation of the hazards, which often means understanding the full spectrum of impacts of extreme events and also the potential connections between them. Indeed, such connections may even threaten the continued economic viability of corporations, insurers and utilities that do not sufficiently investigate them and act on this knowledge. The need to properly incorporate long-term vulnerabilities from factors such as climate change and socioeconomic shifts poses a major challenge to a business model where contracts are typically revised on an annual basis and are thus inherently short term. As climate change progresses, assumptions regarding probabilities of extreme events will need to be periodically updated, and changes in exposure and infrastructure vulnerability will need to be accounted for. Analyses and policies dependent on such updates will necessarily contain greater uncertainty, with a smaller (or non-existent) comparable historical record to refer to. Further collaborations that leverage the statistical expertise and computational power of (re)insurers and the scientific understanding and techniques of climate researchers have large potential to illuminate this future more clearly 79 .

Quantitative and conceptual methods

Considering societal attributes and response capacities in addition to climate factors and traditional impact models is a daunting challenge. However, targeted methodologies informed by the particular type or location of impact can begin to decompose the complexity and diversity of connected extremes. Some uncertainties surrounding the ‘event space’ of connected extremes can be confronted with techniques aimed at constraining the underlying compound physical drivers. We note a selection of these from the climate literature in Table 2 under ‘Statistical approaches’ and ‘Modelling approaches’, and refer interested readers to refs. 8 , 13 for a more complete description.

Disentangling the physical–societal interactions that characterize connected extremes, in contrast, requires highly flexible and less quantitative methods to ensure usability and robustness in the face of deep and complex uncertainties (Table 2 ; see the section titled ‘Socio-physical approaches’). For instance, the adaptive pathway approach 80 recognizes that the ‘decision space’ can be highly sensitive to climate change, political or financial resources, or other contexts, and may exhibit qualitative jumps at certain ‘tipping point’ thresholds 81 . Storylines and scenario-planning methods about potential large-impact events allow for the engagement of stakeholders and the public in identifying crucial factors, chains of causality and ‘tail risks’ through a collaborative process unencumbered by the usual focus on quantification 71 , 82 , 83 . Stress testing explores the ‘impacts space’ associated with connected extremes’ imprint on a given sector or location, highlighting where impact sensitivities are largest in response to slight changes in physical drivers 84 , 85 .

In general, these approaches lead to fewer but more reliable conclusions than conventional climate impacts studies, especially for connected extremes with little or no precedent. Being non-probabilistic, they require careful evaluation by sectoral experts to interpret their outcomes. However, critical test levels can be associated with societal mechanisms, such as supply chains, enabling assessment of the type and severity of extremes that could plausibly cause important disruptions. Specific types of model validation and improvement which could further inform the study of connected extremes include incorporating memory of how previous extremes have affected risk through the depletion of resources, divergence of development pathways, degradation of vulnerability or alteration of exposure, and also better accounting for systemic connections between regions and/or sectors through markets, resource pools or decision-making frameworks.

True coalescence around shared definitions, best practices and research priorities can only occur through sustained and in-depth conversations where sector experts, stakeholders, policymakers and practitioners meaningfully shape the research process from conceptualization to results to implementation. This process has been described by many terms, including ‘co-production’ 86 , 87 , ‘joint problem formulation’ 88 , ‘co-development’ 89 , ‘design thinking’ 90 and ‘bottom-up approaches’ 11 . The underlying principles are consistent: to identify critical constraints and interactions (from ethnography, expert solicitation, process-based impact models and/or systems analysis), and then to use these to iteratively formulate the questions that guide systematic study of the climate. In our view, connected extreme events are too idiosyncratic to allow for a prescribed ‘best’ approach a priori.

Expecting the unexpected

Thorough investigation of connected extremes is often limited by the quantity and type of suitable historical data and model simulations, for both drivers and impacts. For example, variables that play key roles in modulating many connected extremes (for example, wind speed and humidity) are not widely observed at fine temporal resolutions and have short periods of record, but would greatly aid in observational analyses and model validations. In some regions, this problem includes core variables, such as precipitation. Essential vulnerabilities and interactions between decision-making entities remain exogenous to most assessments of climate extremes or are not well characterized at all, leading to uncertainties as basic as the primary cause of impacts from historical connected extremes. Qualitative identification of connections can similarly be limited by data availability. Resolving such questions would aid in building overall confidence about how extreme impacts develop: which systems break down, why, and who is affected when that happens.

The need for skilful forward-looking assessments is underscored by the rapidity of projected twenty-first century warming, which will result in historical conditions always providing incomplete information on the contemporaneous range of possibilities 12 . Therefore, the coming decades will no doubt see previously unanticipated or newly important combinations of extremes 66 . Additionally, risk relationships may change in a qualitative way, such as the emergence of summertime drought–heat interactions in historically cool-summer regions 52 or the increased risk of compound flooding due to sea-level rise 45 . Stretching the ‘event space’ in this way may result in cultural, economic, ecological and/or technological responses that reciprocally shape exposures, vulnerabilities and, perhaps, the anthropogenic forcing itself 91 , 92 .

Climate-system knowledge that provides information about poorly constrained risks from connected extreme events is crucial in helping determine the range of necessary actions. Communication about such scenarios could be key for mobilizing all sectors of society to consider their interfaces with other sectors and the ways in which these interactions cause them to be at risk from connected extreme events. Tools and frameworks for assessing these risks could therefore aid in making increasingly severe connected extreme events a central part of the overall climate change discussion, including via financial and legal mechanisms 93 .

Conclusions and recommendations

The complex and contingent nature of connected extreme events causes them to possess several attributes distinct from those associated with isolated or univariate extreme events. These include a large, poorly characterized sensitivity to small changes in mean climate conditions and a low availability of data on important physical and societal characteristics. Together, these lead to a heightened risk of crossing unknown tipping points in terms of response capacity. Because connection between extreme events depends heavily on situational factors such as season, location and groups affected, essential ingredients for making progress in addressing them include careful impacts-oriented analysis, usage of higher-order metrics and collection of high-quality, high-resolution impacts data. This is an area where the power of emerging computational and communication technologies is likely to be keenly felt.

We consider the climate science community’s role as designing the research-side companion element to the critical decision-making challenges associated with connected extremes 81 , ensuring that scientific information is provided in a way that is congruent to existing decision-making pathways 86 , 94 . The bounds of the ‘decision space’ may significantly shape the roles of scientists and decision makers: problems with long-term aspects or a wide range of potential policy solutions are most likely to be usefully informed by climate research, while actions with a narrower scope and sensitive cultural or political considerations are weighted toward decision makers.

To the extent possible, collaborations should include determining major feedbacks between physical processes and societal decisions that most affect the final impact. Stated differently, impacts can serve as a winnowing device to identify what combinations of extreme events matter. This knowledge gathering can also incentivize the selection of a more effective mix of policies, including robust or flexible adaptation strategies that provide benefits under a range of connected climate and impact outcomes, by better foreseeing relevant societal and environmental changes over the timescale of the investment 91 . The COVID-19 pandemic represents a dramatic object lesson in how unprecedented events can create or exacerbate correlated risks related to both climatic and non-climatic stressors, amplifying impacts but offering opportunities for shared learning and long-term resilience. Lastly, impacts-driven research efforts can reveal particular disciplines where the presence of specialists would be especially valuable—there is the potential for fruitful exchanges to take place between researchers in the climate domain and experts in engineering, statistics, health, urban planning, sociology, psychology, finance, ecology and emergency management, among others. It is often only through such detailed conversations that essential incentives and constraints come to light and that conceptual paradigms shift 95 .

Most broadly, we argue for promoting mechanisms to recognize the components of a connected extreme event as such, and to gather and share important information about them to facilitate risk management across all levels of decision-making. At a recent workshop, few participants knew of any examples in which connected extremes had been included in planning guidelines. This communication barrier also exists within the physical science community, where examples emerged of certain genres of events (for example, local situations) for which the necessary resources have not yet been marshalled to examine the connectivity or full implications as might be seen when looking through a wider lens. The strong modulation of the impacts of connected extremes via complex societal systems demands serious and sustained efforts to facilitate geographic and cross-domain knowledge exchange, such that climate research results can lead to well-informed pre-event preparation and post-event recovery, ultimately aiding in the amelioration of the serious impacts that connected extremes often produce. Facing this challenge, some encouragement might come from the analogous example of aviation, where physical science, engineering and social sciences have come together to successfully mitigate—despite greatly increasing system complexity—the frequency of disastrous failures, which tend to result only from the concatenation of many low-probability events.

Data availability

Data used in Fig. 2 are available from the corresponding author upon reasonable request. The data are not publicly available as they are part of a commercially proprietary dataset.

Code availability

Code for reproducing Figs. 2 and 3 has been archived at https://doi.org/10.5281/zenodo.3714226 .

Change history

22 june 2020.

In the version of this Perspective originally published, ‘Temporal compounding, concurrent’ in Fig. 2 should have read ‘Temporal compounding, concurrence’; this has now been corrected in the online versions.

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Acknowledgements

This paper was developed from ideas discussed at a May 2019 workshop at Columbia University, organized by C.R., R.M.H., J.Z., O.M., A.A., S.J.C., M.O., A.C.R., T.W., N. Diffenbaugh, S. I. Seneviratne and A. Sobel ( http://extremeweather.columbia.edu/workshop-on-correlated-extremes/ ). The workshop drew generous support from the U.S. National Science Foundation’s Prediction of and Resilience against Extreme Events (PREEVENTS) program, Aon, the Columbia University Initiative on Extreme Weather and Climate, NOAA’s Consortium for Climate Risk in the Urban Northeast (CCRUN), the World Climate Research Programme’s (WCRP) Grand Challenge on Weather and Climate Extremes, and the European COST Action ‘Understanding and modeling compound climate and weather events’ (DAMOCLES; CA17109). A portion of C.R.’s work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. R.M.H acknowledges support from the NOAA RISA Program (grant no. NA15OAR4310147). J.Z. acknowledges financial support from the Swiss National Science Foundation (Ambizione grant no. 179876). O.M. acknowledges financial support from the Swiss National Science Foundation (grant no. 178751). T.W. acknowledges financial support from the National Science Foundation (grant no. AGS-1929382).

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Radley M. Horton, Suzana J. Camargo & Kai Kornhuber

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C.R., R.M.H., J.Z. and O.M. developed the initial concept. C.R. created figures and S.G.B. provided data for Fig. 2 . C.R. led the writing of the manuscript, and all authors contributed to writing and editing.

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Raymond, C., Horton, R.M., Zscheischler, J. et al. Understanding and managing connected extreme events. Nat. Clim. Chang. 10 , 611–621 (2020). https://doi.org/10.1038/s41558-020-0790-4

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Extreme Weather on Earth

Anna Mika, National Geographic Education

In this activity, students use a set of photographs and a 3-minute video on weather to investigate extreme weather events. They are posed with a series of questions that ask them to identify conditions predictive of these events, and record them on a worksheet. Climate and weather concepts are defined.

Notes from our reviewers

The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials .

• Teaching Tips Educators are encouraged to start the activity by activating students' prior knowledge about extreme weather on Earth. As an extension to this activity, educator could encourage students to investigate what constitutes extreme weather. In some areas, certain weather-related events may not be classified as extreme.
• About the Science Students investigate types of extreme weather and their contributing factors, and then explore similarities and differences between weather and climate. Comment from expert scientist: Good overview and use of imagery. Language is appropriate.
• About the Pedagogy Video and brilliant photography archived on the National Geographic Society's website make this lesson stimulating; otherwise, it is a standard paper-and-pencil activity. Text is provided underneath photographs, explaining the images.
• Technical Details/Ease of Use Educator is given clear instructions on how to introduce and guide this activity. No transcript on the video is provided.

Attribution of Extreme Weather Events in the Context of Climate Change (2016)

Chapter: 5 conclusions, chapter five, conclusions.

In the past decade, the field of extreme event attribution has made great strides in understanding and explaining extreme events in the context of climate change. This is still an emerging science, however; thus, continued research is required to increase the reliability of event attribution results, particularly for event types that are presently poorly understood. The need for improved understanding is coming at a time when there is increasing inquiry by the public, policy makers, and practitioners about the relationship between specific weather events and climate change (e.g., the question, “Is it caused or affected by climate change?”). Advances in the field will depend not only on addressing scientific problems specific to attribution but also on advances in the basic underlying science, including observations, weather and climate modeling, statistical methodology, and theoretical understanding of extreme events and their relation to climate.

This chapter builds on the information presented in the preceding chapters to provide guidance for framing questions about event attribution and approaches to ensuring the robustness and reliability of event attribution studies and information. The committee also recommends future research that would improve extreme event attribution capabilities and discusses the future of event attribution in an operational context.

ASSESSMENT OF CURRENT CAPABILITIES

Event attribution is more reliable when based on sound physical principles, consistent evidence from observations, and numerical models that can replicate the event. The ability to attribute the causes of some extreme event types has advanced rapidly since the emergence of event attribution science a little over a decade ago, while attribution of other event types remains challenging. In general, confidence in attribution results is strongest for extreme event types that

• have a long-term historical record of observations to place the event in an appropriate historical context;
• are simulated adequately in climate models; and
• are either purely meteorological in nature (i.e., the nature of the event is not strongly influenced by the built infrastructure, resource management actions,
• etc.) or occur in circumstances where these confounding factors can be carefully and reliably considered.

Non-meteorological factors confound observational records and can limit the accuracy of model simulations of extreme events. Drought and wildfire are examples of events for which non-meteorological factors can be especially challenging in attribution studies.

Furthermore, confidence in attribution results that indicate an influence from anthropogenic climate change is strongest when

• there is an understood and robustly simulated physical mechanism that relates a given class of extreme events to long-term anthropogenic climate changes such as global-scale temperature increase or increases in water content of a warmer atmosphere.

Confidence in attribution findings of anthropogenic influence is greatest for those extreme events that are related to an aspect of temperature, such as the observed long-term warming of the regional or global climate, where there is little doubt that human activities have caused an observed change. For example, a warmer atmosphere is associated with higher evapotranspiration rates and heavier precipitation events through changes in the air’s capacity to absorb moisture. Atmospheric circulation and dynamics play some role, however, which is different for different event types. Changes in atmospheric circulation and dynamics are generally less directly controlled by temperature, less robustly simulated by climate models, and less well understood. Event attribution can be further complicated by the existence of other factors that contribute to the severity of impacts.

Confidence in attribution analyses of specific extreme events is highest for extreme heat and cold events, followed by hydrological drought and heavy precipitation. There is little or no confidence in the attribution of severe convective storms and extratropical cyclones. Confidence in the attribution of specific events generally increases with our understanding of the effect of climate change in the event type. Nevertheless, the gap between this understanding and confidence in attribution of specific events varies among event types.

Attribution of events to anthropogenic climate change may be complicated by low-frequency natural variability, which influences the frequencies of extreme events on decadal to multidecadal timescales. The Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation are examples of such variability. Characterization of these influences is uncertain because the observed record is too short to do so reliably, and it also is too short to assess whether climate models simulate these modes of variability correctly.

PRESENTING AND INTERPRETING EXTREME EVENT ATTRIBUTION STUDIES

There is no single best method or set of assumptions for event attribution because these depend heavily on the framing of the question and the amount of time available to answer it. Time constraints may themselves affect framing and methodological choices by limiting analyses to approaches that can be undertaken quickly.

A definitive answer to the commonly asked question of whether climate change “caused” a particular event to occur cannot usually be provided in a deterministic sense because natural variability almost always plays a role. Many conditions must align to set up a particular event. Extreme events are generally influenced by a specific weather situation, and all events occur in a climate system that has been changed by human influences. Event attribution studies generally estimate how the intensity or frequency of an event or class of events has been altered by climate change (or by another factor, such as low-frequency natural variability).

Statements about attribution are sensitive to the way the questions are posed and the context within which they are posed. For example, when defining an event, choices must be made about defining the duration of the event (when did it begin and when did it end) and the geographic area it impacted, but this may not be straightforward for some events (e.g., heat waves). Furthermore, different physical variables may be studied (e.g., drought might be characterized by a period with insufficient precipitation, excessively dry soil, or reduced stream flow), and different metrics can be used to determine how extreme an event was (e.g., frequency, magnitude). Whether an observation- or model-based approach is used, and the sorts of observations and/or models available for studying the event, also will constrain the sorts of questions that can be posed.

Attribution studies of individual events should not be used to draw general conclusions about the impact of climate change on extreme events as a whole. Events that have been selected for attribution studies to date are not a representative sample (e.g., events affecting areas with high population and extensive infrastructure will attract the greatest demand for information from stakeholders). In addition, events that are becoming less likely because of climate change (e.g., cold extremes) will be studied less often because they occur less often than events whose frequency is increasing because of climate change. Furthermore, attribution of individual events is generally more difficult than characterizing the statistical distribution of an event of a given type and its dependence on climate. For all of these reasons, counts of available attribution studies with either positive or negative or neutral results are not expected to give a reliable indication of the overall importance of human influence on extreme events.

Unambiguous interpretation of an event attribution study is possible only when the assumptions and choices that were made in conducting the study are clearly stated and the uncertainties are carefully estimated. The framing of event attribution questions, which may depend strongly on the intended application of the study results, determines how the event will be studied and can lead to large differences in the interpretation of the results. Event attribution studies presented in the following manner are less likely to be misinterpreted:

• Assumptions about the state of one or more aspects of the climate system at the time of the event (e.g., sea-surface temperature [SST] anomalies, atmospheric circulation regimes, specific synoptic situations) are clearly communicated.
• Estimates of changes in both magnitude and frequency are provided, with accompanying estimates of uncertainty, so users can understand the estimated degree of change from the different perspectives.
• Estimates of changes in frequency are presented as a risk ratio: that is, in terms of the ratio of the probability of the event in a world with human-caused climate change to its probability in a world without human-caused climate change. Equivalently, one can compare the return periods of the event (i.e., how rarely an event occurs) in the world without climate change to that in the world with climate change.
• The impact of assumptions (e.g., of how estimates of changes in magnitude and frequency depend on SST anomalies or atmospheric circulation regimes) is discussed.
• Statements of confidence accompany results so users understand the strength of the evidence.

Bringing multiple scientifically appropriate approaches together, including multiple models and multiple studies, helps distinguish results that are robust from those that are much more sensitive to how the question is posed and the approach taken. Utilizing multiple methods to estimate human influences on a given event also partially addresses the challenge of characterizing the many sources of uncertainty in event attribution.

Examples of multiple components that can lead to more robust conclusions include:

• Estimates of event probabilities or effect magnitudes based on an appropriate modeling tool that has been shown to reasonably reproduce the event and its circumstances, such as the dynamic situation leading to the event.
• Reliable observations against which the model has been evaluated and that give an indication of whether the event in question has changed over time in a manner that is consistent with the model-based attribution.
• Assessment of the extent to which the result is consistent with the physical understanding of climate change’s influence on the class of events in question.
• Clear communication of remaining uncertainties and assumptions made or conditions imposed on the analysis.

THE PATH FORWARD

Improving extreme event attribution capabilities.

A focused effort to improve understanding of specific aspects of weather and climate extremes could improve the ability to perform extreme event attribution. The World Climate Research Programme (WCRP) has identified climate extremes as one of its grand challenges, suggesting major areas of scientific research, modeling, analysis, and observations for WCRP in the next decade. Because extreme event attribution relies on all aspects of the understanding of extremes and their challenges, the committee endorses the recommendations from the white paper “WCRP Grand Challenge: Understanding and Predicting Weather and Climate Extremes” ( Box 5.1 ; Zhang et al., 2014 ) as necessary to make advances in event attribution. Advances made in understanding the physical mechanisms and in improving the realism of extreme events in weather and climate models will benefit event attribution studies.

The committee recommends that research that specifically aims to improve event attribution capabilities include increasing the understanding of

• the role of dynamics and thermodynamics in the development of extreme events;
• the model characteristics that are required to reliably reproduce extreme events of different types and scales;
• changes in natural variability, including the interplay between a changing climate and natural variability, and improved characterization of the skill of models to represent low-frequency natural variability in regional climate phenomena and circulation;
• the various sources of uncertainty that arise from the use of models in event attribution;
• how different levels of conditioning (i.e., the process of limiting an attribution analysis to particular types of weather or climate situations) lead to apparently different results when studying the same event;
• the statistical methods used for event attribution, objective criteria for event selection, and development of event attribution evaluation methods;
• the effects of non-climate causes—such as changes in the built environment (e.g., increasing area of urban impervious surfaces and heat island effects), land cover changes, natural resource management practices (e.g., fire suppression), coastal and river management (e.g., dredging, seawalls), agricultural practices (e.g., tile drainage), and other human activities—in determining the impacts of an extreme event;
• expected trends in future extreme events to help inform adaptation or mitigation strategies (e.g., calculating changes in return periods to show how the risk from extreme events may change in the future); and
• the representation of a counterfactual world that reliably characterizes the probability, magnitude, and circumstances of events in the absence of human influence on climate.

Research that is targeted specifically at extreme events, including event attribution, could rapidly improve capabilities and lead to more reliable results. In particular, there are opportunities to better coordinate existing research efforts to further accelerate the development of the science and to improve and quantify event attribution reliability. Examples of event attribution research coordination include EUropean CLimate and weather Events: Interpretation and Attribution (EUCLEIA), weather@home, World Weather Attribution (see Box 3.4 for additional information on these), and the International Detection and Attribution Group (IDAG), all of which also coordinate with one another. Furthermore, given that event attribution spans climate and weather, the field would benefit from interdisciplinary research at the interface between the climate, weather, and statistical sciences to improve analysis methods. Event attribution capabilities would be improved with better observational records, both near–real time and for historical context. Long, homogeneous observed

records are essential for placing events into a historical context and for evaluating to what extent climate models reliably simulate the effect of decadal climate variability on extremes.

Event attribution could be improved by the development of transparent community standards for attributing classes of extreme events. Such standards could include an assessment of model quality in relation to the event/event class. Community agreement is needed on when a model represents a given event type well enough for attribution studies to be possible. At present, such standards do not clearly exist, and some model-based attribution studies do not even attempt to assess model adequacy. Such standards are critical for enhancing confidence in event attribution studies. Other examples of necessary community standards include use of multiple lines of evidence, development of a transparent link to a detected change that influences events in question, and clear communication of sensitivities of the result to framing of the event attribution question.

Systematic criteria for selecting events to be analyzed would minimize selection bias and permit systematic evaluation of event attribution performance, which is important for enhancing confidence in attribution results. Studies of a representative sample of extreme events would allow stakeholders to use such studies as a tool for understanding how individual events fit into the broader picture of climate change. Irrespective of the method or related choices, it would be useful to develop a set of objective criteria to guide event selection. A simple example of an objective approach might be to select events based on their rarity in the historical record using a fixed threshold, such as 24-hour precipitation events throughout a given domain that exceed the local 99th percentile of historical precipitation events. It should be noted, however, that even in this case, subtleties associated with historical quantile definition would need to be considered. The development of objective criteria for event selection would help both to reduce selection bias and to lead to methodological improvements. A path forward to avoiding selection bias is to perform event attribution on a predefined set of events of several different types that could reasonably be expected to occur in the current climate. This could involve systematic definition of events or consideration of events based on the full historical record and not just current events. Christidis and colleagues (2014) describe one example of such an approach: namely, a method for precomputing estimates of how human influence has changed the odds of extremely warm regional seasonal mean temperatures based on a formal detection and attribution methodology (see Chapter 3 ). Another example is the approach of trying to identify “grey swan tropical cyclones” (events not seen before, but theoretically possible) before they occur ( Lin and Emanuel, 2015 ).

Event selection criteria also is a prerequisite for the development of a formalized approach to evaluating event attribution results and uncertainty estimates. Such evaluation is important for establishing confidence in event attribution statements. Development of such an approach could be modeled after existing approaches used to evaluate weather forecasts. One possible approach to evaluation would be to use a large sample of objectively selected events on a global scale to evaluate if, on average, model predictions or simulations of extreme events are on target. This could involve seasonal and decadal predictions of the number of events of a certain type based on simulations with external drivers only. Events that become more frequent with global warming, as well as events that become less frequent, such as cold spells, would be included in such an approach.

Event Attribution in an Operational Context

As more researchers begin to attempt event attribution, their efforts can benefit from coordination to improve analysis methods and work toward exploring uncertainties across methods and framing. Event attribution can benefit from links to operational numerical weather prediction where available. As discussed in Chapter 3 (see also Box 3.4 ), some groups are moving toward the development of operational extreme event attribution systems to systematically evaluate the causes of extreme events based on predefined and tested methods. Objective approaches to compare and contrast the analyses among multiple different research groups based on agreed event selection criteria are yet to be developed.

In the committee’s view, a successful operational event attribution system would have several key characteristics. First is the development and use of objective event selection criteria to reduce selection bias so stakeholders understand how individual events fit into the broader picture of climate change. Second is the provision of stakeholder information about causal factors within days of an event, followed by updates as more data and analysis results become available. This is analogous to such other fields as public health and economics, where it is acceptable to revise initial forecasts and analyses as more data become available (e.g., Gross Domestic Product estimates, recession start and stop dates, etc.). A third characteristic of a successful event attribution system is clear communication of key messages to stakeholders about the methods and framing choices as well as the associated uncertainties and probabilities. Finally, reliable assessments of performance of the event attribution system are needed. Such assessments could be developed through processes utilizing regular forecasts of event probability and intensity, observations, and skill scores similar to those used routinely in weather forecasting for evaluation. Rigorous approaches to

managing and implementing system improvements also are a critical element of these assessments.

Some future event attribution activities could benefit from being linked to an integrated weather-to-climate forecasting effort on a range of timescales. The development of such an activity could be modeled from concepts and practices within the Numerical Weather Prediction (NWP) and seasonal forecasting community. NWP, which dates back to the 1950s, is focused on taking current observations of weather and processing these data with computer models to forecast the future state of weather. A project linking attribution and weather-to-climate forecasting likewise could build on recent efforts to increase national and international capacity to forecast the likelihood of extreme events at subseasonal-to-seasonal timescales 1 ( WMO, 2013 ).

Ultimately the goal would be to provide predictive (probabilistic) forecasts of future extreme events at lead times of days to seasons, or longer, accounting for natural variability and anthropogenic influences. These forecasts would be verified and evaluated utilizing observations, and their routine production would enable the development and application of appropriate skill scores (using appropriate metrics to define and track the skill). The activity would involve rigorous approaches to managing and implementing system enhancements to continually improve models, physical understanding, and observations focused on extreme events.

Correctly done, attribution of extreme weather events can provide an additional line of evidence that demonstrates the changing climate as well as its impacts and consequences. An accurate scientific understanding of extreme weather event attribution can be an additional piece of evidence needed to inform decisions on climate change–related actions.

The committee also encourages continued research in event attribution outside of an operational context to ensure further innovation in the field. This would facilitate better understanding of a breadth of approaches, framings, modeling systems, and the performance of event attribution methods across past events, including in the longer historical context.

__________________

1 Another National Academies of Sciences, Engineering, and Medicine committee is studying this topic and will produce a report in the spring of 2016: http://dels.nas.edu/Study-In-Progress/Developing-Research-Agenda/DELS-BASCPR-13-05 .

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As climate has warmed over recent years, a new pattern of more frequent and more intense weather events has unfolded across the globe. Climate models simulate such changes in extreme events, and some of the reasons for the changes are well understood. Warming increases the likelihood of extremely hot days and nights, favors increased atmospheric moisture that may result in more frequent heavy rainfall and snowfall, and leads to evaporation that can exacerbate droughts.

Even with evidence of these broad trends, scientists cautioned in the past that individual weather events couldn't be attributed to climate change. Now, with advances in understanding the climate science behind extreme events and the science of extreme event attribution, such blanket statements may not be accurate. The relatively young science of extreme event attribution seeks to tease out the influence of human-cause climate change from other factors, such as natural sources of variability like El Niño, as contributors to individual extreme events.

Event attribution can answer questions about how much climate change influenced the probability or intensity of a specific type of weather event. As event attribution capabilities improve, they could help inform choices about assessing and managing risk, and in guiding climate adaptation strategies. This report examines the current state of science of extreme weather attribution, and identifies ways to move the science forward to improve attribution capabilities.

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