Climate Change Risk to National Critical Functions


Jul 10, 2024

Cars crossing the Golden Gate Bridge in San Francisco under a smoky orange sky caused by California wildfires, photo by bennymarty/Getty Images

Cars crossing the Golden Gate Bridge in San Francisco under a smoky orange sky caused by California wildfires

Photo by bennymarty/Getty Images

It was early evening when the storm hit. Amid blinding rain, rivers and streams jumped their banks and surged into downtown Ellicott City, Maryland. The water swept through buildings and sent parked cars careening down Main Street. Two people died.

Experts described what happened that night in July 2016 as a thousand-year flood. Then it happened again. In May 2018, six inches of rain pounded the hills above Ellicott City in less than three hours. Another river of brown water crashed through downtown, scouring out homes and businesses. One person died.

Climate models show such extreme storms doubling in frequency by the end of this century, over historical averages. U.S. cities may endure 60 percent more days of extreme heat than they're used to. Global sea levels could rise by more than four feet.

Researchers at RAND have been working with the federal government to anticipate how the changing climate will strain the basic functions that underpin American society. They have identified dozens of core services that will face regional- or even national-level disruptions in the years to come. Those include supplying water and electricity, providing medical care—and responding to emergencies like the floods in Ellicott City.

View of Ellicott City, Maryland, after historic flash flooding in the downtown area on July 31, 2016, photo by mpi34/MediaPunch/IPX

View of Ellicott City, Maryland, after historic flash flooding in the downtown area on July 31, 2016

Photo by mpi34/MediaPunch/IPX

“It's a new way of thinking about risks that people might not have thought about in the context of climate change,” said Susan Resetar, a senior operations researcher at RAND. “It's a way to focus attention, to prioritize resources: Here is what we're seeing. Let's start the conversation and dive into this.”

The United States used to experience around three billion-dollar weather disasters a year, adjusted for inflation, federal numbers show. By the early 2000s, that had risen to six. In the 2010s, it was more like 13. During the past five years, the U.S. has averaged around 20 billion-dollar disasters every year. And last year, the number was 28.

That mostly reflects physical damage—lost homes, lost businesses, downed power lines, broken levees. A few years ago, the national Cybersecurity and Infrastructure Security Agency, part of the U.S. Department of Homeland Security, came up with a much broader way to look at risk. It identified 55 government and private-sector functions that are so critical that a disruption would threaten national security, safety, health, or the economy. It describes them as the “operational backbone for modern society.” It asked RAND to assess the risk that climate change poses to each of them.

That effort has come to involve more than two dozen researchers. They include experts in climate change and climate resilience, as well as experts in individual functions. They dug through years of studies, assessments, and climate projections. Then they rated the impact that climate change will likely have, function by function, on a national level.

Hurricane Katrina would have been a 3 on their 5-point scale, a regional catastrophe, but not one that disrupted functions far from the Gulf Coast. COVID's impact on education was a 4. The total shutdown of air travel after the attacks of Sept. 11 is what a 5 looks like.

The United States used to experience around three billion-dollar weather disasters a year. By the early 2000s, that had risen to six. In 2023, there were 28.

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Nearly half of the nation's critical functions will face at least moderate disruptions—level 3—by 2050, the researchers found. Nearly two-thirds will experience that Katrina-level of risk by 2100, even with no increases in carbon emissions. That means they won't be able to meet routine operational needs in at least some parts of the country.

Providing medical care, for example. It will face level-3 disruptions by 2050 in part because of the damage that flooding or hurricanes might do to hospitals and other medical facilities. But the health care system will also have to contend with a growing risk of disease in a warming world.

Transmitting electricity will also be at level 3 by then. Wildfires will tear through power lines; extreme heat will make them soften and sag. But at the same time, demand for electricity will only increase as temperatures rise. And on the hottest days, when demand is highest, workers won't be able to spend as much time outside doing maintenance.

Two key functions will face COVID levels of disruption by the end of this century. Extreme weather will threaten almost every link in the supply chains that deliver everything from car parts to medical supplies. And extreme drought, along with infrastructure-battering hurricanes and wildfires, will strain the nation's ability to supply water, especially across the Western United States.

None of the functions face the most severe, level-5 risks in the next few decades. But one, providing technology products and services, such as microchips, could get there by 2100. Researchers initially overlooked it as a major vulnerability. But the industry is highly concentrated in places that are already seeing extreme weather. When a winter storm swept through Texas in 2021, for example, it damaged several chip-manufacturing plants, slowing production for months.

“Not every critical function is vulnerable in the same way. Some have greater needs than others, and some might surprise you,” said senior information scientist Michelle Miro. “But if you're looking for where to prioritize funding, where to get the most bang for your buck, there's one other thing to keep in mind. They're all connected and dependent on one another.”

Agriculture, for example, might see some modest, level-2 disruptions by 2050, mostly from changing weather patterns and drought. But that risk rating only reflects the direct climate impacts to agriculture itself, not any disruptions to other critical functions that agriculture relies on. Farmers won't get far without water or electricity, for example, and those will be facing their own, much more serious disruptions by 2050.

The researchers analyzed how such upstream disruptions could increase every function's exposure to risk in the years to come. But they didn't factor those dependencies into their final risk ratings. For one thing, they often didn't have enough information to predict how immediate or impactful those cascading disruptions will be. For another: “Everything would be high,” Miro said. “Anything that needs power, for example, will be at risk of disruption if severe weather damages distribution equipment.”

In fact, the researchers identified four critical functions on which all others depend: maintaining supply chains; providing medical care; providing tech products and services; and preparing for and managing emergencies. All four face Katrina-level disruptions, or worse, by 2050.

The research team is now narrowing its focus to specific regions of the United States. The next Hurricane Katrina might still only cause level-3 disruptions on a national scale. But on a regional scale, it might well be another 5. Those regional assessments also include real-world case studies that show in greater detail how a disruption in one function, like generating power, can cascade and take out others.

A car drives under dangerous trees weighed down by ice and powerlines after an icestorm, photo by DenisTangneyJr/Getty Images

A car drives under dangerous trees weighed down by ice and powerlines after an icestorm

Photo by DenisTangneyJr/Getty Images

Researchers have also started to catalog the options available to prevent—or at least mitigate—the coming climate risks. They identified more than 250 strategies that would strengthen some of the most vulnerable functions. Those range from building sea walls and recycling water to updating building codes and raising awareness. Some of the public safety functions, like emergency response, just need more people.

“These critical functions are really the things we need to continue our day-to-day lives,” senior researcher Andrew Lauland said. “Climate change is such a daunting, huge thing for people to wrap their arms around. This allows us to focus the conversation on where we're really vulnerable, where we're really at risk, so we can start talking productively about what to do about it.”

Lauland previously worked as the director of homeland security for the State of Maryland. He came to RAND in 2015, not long before back-to-back thousand-year storms slammed into Ellicott City. “I was part of the last period when we were lucky enough to not be in almost a permanent response phase in emergency management,” he said.

“It used to be you'd respond to a disaster, then recover, then prepare for the next one,” he said. “You had a hurricane season, and then it stopped. Now, you try to recover and prepare while you're constantly responding. I was on the tail end of the group that actually used to get a break.”

National Critical Function Risk Ratings Under Current Emissions


  • 1. No disruption or normal operations
  • 2. Minimal disruption
  • 3. Moderate disruption
  • 4. Major disruption
  • 5. Critical disruption
Rating Function 2050 2100
Moderate to Critical Provide Information Technology Products and Services 4 5
Supply Water 3 4
Maintain Supply Chains 3 4
Fuel Refining and Processing Fuels 3 3
Exploration and Extraction of Fuels 3 3
Transport Cargo and Passengers by Vessel 3 3
Transport Cargo and Passengers by Air 3 3
Moderate Provide Housing 3 3
Provide Materiel and Operational Support to Defense 3 3
Produce and Provide Human and Animal Food Products and Services 3 3
Provide Public Safety 3 3
Provide Medical Care 3 3
Support Community Health 3 3
Prepare for and Manage Emergencies 3 3
Manage Wastewater 3 3
Manage Hazardous Materials 3 3
Enforce Law 3 3
Develop and Maintain Public Works and Services 3 3
Transport Materials by Pipeline 3 3
Transport Cargo and Passengers by Road 3 3
Transmit Electricity 3 3
Distribute Electricity 3 3
Provide Wireline Access Network Services 3 3
Provide Wireless Access Network Services 3 3
Provide Cable Access Network Services 3 3
Provide Metals and Materials 2 3
Produce Chemicals 2 3
Produce and Provide Agricultural Products and Services 2 3
Manufacture Equipment 2 3
Generate Electricity 2 3
Provide Insurance Services 2 3
Provide and Maintain Infrastructure 2 3
Transport Cargo and Passengers by Rail 2 3
Educate and Train 2 3
Transport Passengers by Mass Transit 2 3
Minimal Store Fuel and Maintain Reserves 2 2
Provide Radio Broadcast Access Network Services 2 2
Protect Sensitive Information 2 2
Preserve Constitutional Rights 2 2
Perform Cyber Incident Management Capabilities 2 2
Operate Government 2 2
Conduct Elections 2 2
Lowest Risk Provide Payment, Clearing, and Settlement Services 2 1
Provide Funding and Liquidity Services 2 1
Provide Capital Markets and Investment Activities 2 1
Research and Development 1 2
Provide Internet Routing, Access, and Connection Services 1 2
Operate Core Network 1 2
Provide Wholesale Funding 1 1
Provide Identity Management and Associated Trust Support Services 1 1
Provide Consumer and Commercial Banking Services 1 1
Maintain Access to Medical Records 1 1
Provide Satellite Access Network Services 1 1
Provide Positioning, Navigation, and Timing Services 1 1
Provide Internet Based Content, Information, and Communication Services 1 1