The Future of Extreme Heat in Cities

What We Know — and What We Don’t

Extreme heat is becoming more frequent and more intense in cities around the world due to climate change. As global temperatures rise, heatwaves are lasting longer, happening more often, and reaching higher temperatures. This intensifying urban heat island effect threatens the health, economies, and infrastructure of cities – and vulnerable populations are being impacted the most.

There’s still a lot we don’t fully understand about the future of extreme urban heat. But researchers have made significant progress in recent years studying heat patterns, identifying risks, and finding solutions.

This article will provide an overview of the latest science and projections related to escalating extreme heat in cities. We’ll look at what researchers know – and what they don’t yet know – about the scope of the threat, who is most vulnerable, how cities can enhance resilience in the face of uncertainty, and more. We’ll also highlight some of the most promising and innovative adaptation strategies cities are implementing to keep people safe during extreme heat events now and in the coming decades.

What Do We Know About the Future of Extreme Urban Heat?

Here’s a high-level summary of some of the key things researchers understand about intensifying extreme heat in urban areas based on the latest climate models and scientific studies:

Hotter Summers Are a Virtual Certainty

Global temperatures have already risen about 1°C since the late 19th century. And they are essentially locked in to increase further – likely between 1-2°C by the 2050s even if emissions reduction efforts are accelerated.
This means extreme heat days and heatwaves are virtually certain to become more frequent and severe in coming decades in cities worldwide.
Models show that what are currently considered extreme heat events will likely happen two to three times more often by the 2050s. Essentially, today’s rare heatwaves will become the norm during summer months.

Heat Impacts Are Far Reaching

Extreme urban heat threatens public health, economies, infrastructure, and more.
It can directly cause heat stroke and exacerbate other medical conditions. But heat stress also impacts productivity, labor capacity, educational outcomes, and mental health.
High temperatures strain electrical grids due to increased demand for air conditioning. They also expand bridge joints, warp train tracks, buckle pavement, and interfere with other infrastructure.

Cities Are Warming Faster Than Rural Areas

The urban heat island effect, caused by the prevalence of heat-retaining concrete and asphalt as well as waste heat from vehicles, buildings, and industry, means cities are warming at two to three times the rate of rural areas.
U.S. cities are warming on average by 3°C when rural areas around them are warming by 1°C. This magnifies heat risks for urban populations.
Over 70% of people will live in cities by 2050 – meaning heat exposure will be increasingly an urban phenomenon.

Lower-Income Residents Are Most at Risk

While extreme urban heat affects entire metro regions, lower-income groups face the highest health and economic threats.
Hotter cities exacerbate income inequality and accessibility to air conditioning. Lower-income neighborhoods tend to have fewer parks and trees that help dissipate heat. Residents often also have underlying health conditions that make heat more dangerous.

Heat Mortality Varies Widely By Location

Death rates linked to heat stress differ drastically depending on a city’s climate, infrastructure, and population vulnerability.
For example, heat causes 65 deaths per million residents in London compared to over 700 deaths per million residents in Delhi according to one study.
Global warming has increased heat mortality by over 20% in cities worldwide over the past few decades. The specific impacts vary across regions.

What Are Key Unknowns About Intensifying Urban Heat?

While scientists have made huge strides in recent years tracking urban warming patterns, health impacts, and vulnerabilities – major questions remain about the scope of the threat extreme heat poses for cities globally.

Here are some of the most important unknowns researchers are working to unravel:

Exactly How Much Hotter Will Cities Get?

Climate scientists have developed conceptual models of potential warming trajectories. But it remains challenging to predict local temperature increases – especially for urban heat islands.
Researchers are trying to downscale climate projections to improve metro-specific extreme heat forecasts and enable better planning. But this is a complex undertaking with uncertainties.

How Will Heat Interact with Other Climate Change Impacts?

Scientists know extreme urban heat is being intensified by global warming. But less is understood about how it might interact with other climate change effects.
For example, how will heat stress combine with factors like reduced air quality from higher ozone levels or fluctuating disease vectors to impact public health?

What Are the Global Economic Costs of Urban Heat?

Several cities have calculated costs locally from health services, lost productivity and more during heat waves. But few studies have looked comprehensively at national and global-level economic implications.
Better understanding the magnitude of financial costs will be key for spurring investment into adaptation efforts that reduce harm.

How Can Cities Better Predict Extreme Heat Risk Zones?

Improving hyperlocal weather monitoring and modeling is vital for cities seeking to deploy emergency heat relief resources.
Researchers are working on hazardous heat mapping to identify neighborhoods most prone to deadly heat. Enhancing risk prediction will enable better targeting of interventions.

To What Extent Do People Acclimate to Higher Temperatures?

It remains debated how much people can physiologically and behaviorally adjust to intensifying heat over time.
Some studies suggest there are limits, but further research is needed to guide emergency planning and expectations around adapting.

How Much Can Intensifying Heat Be Avoided Through Mitigation?

Scientists recognize that avoiding the worst heat scenarios relies on urgent global emissions reductions.
But few studies clearly quantify how much escalating urban heat could be avoided under different mitigation scenarios. Doing so could help spur climate action.

How Are Cities Planning for Hotter Temperatures?

Despite uncertainties about the extent of future threats, many cities are taking steps to assess risks, create plans, and implement interventions aimed at enhancing resilience in the face of higher heat levels.

Here is an overview of some of the key ways urban leadership can better prepare communities for extreme heat today and in coming decades:

Conduct Risk Assessments

An essential first step is using climate projections and exposure data to model and map metro-wide heat risks. This enables targeted planning.
Cities like New York, Seoul, and Ahmedabad have undertaken comprehensive extreme heat risk analyses to guide adaptation.

Develop Heat Action Plans

Using risk maps and modeling, cities can create localized Heat Action Plans that coordinate emergency responses across agencies when extreme heat thresholds are exceeded.
These plans designate roles for monitoring forecasts, opening cooling centers, adjusting energy use, enforcing worker safety protocols and more during heatwaves.

Invest in Cooling and Shaded Green Space

Expanding green infrastructure like street trees, green roofs, and parks helps dissipate heat in neighborhoods and creates shaded Havens offering temperature relief during heat events.
One recent study found that green spaces can reduce surface temperatures in cities by up to 4°C.

Enhance Building Design Standards

New efficiency codes and standards for construction materials as well as increased use of passive cooling can help reduce waste heat from buildings.
Cool roofs that reflect sunlight and wall shades can also be installed to lower indoor temperatures.

Install Smart Early Warning Systems

Automated extreme heat alert systems notify residents via text, email, radio or cell broadcasts when dangerous conditions are imminent. This allows people to take protective action.
Warning thresholds can be tailored locally based on exposure risks and adapted over time as people’s heat tolerance may shift.

Distribute Targeted Emergency Aid

Social service agencies can distribute bottled water, sunscreen, hats, emergency cooling items and conduct outreach to vulnerable residents during heat emergencies.
Cities like Ahmedabad, India rely on extensive networks of local nonprofits to distribute heat relief based on maps of neighborhoods facing elevated risk levels.

Adjust Infrastructure Operations

Adjusting infrastructure systems in advance of and during extreme heat can reduce cascading technological failures. This includes altering the energy grid, public transit, and construction schedules.
For example, temporary speed restrictions on railways are often imposed during heat waves to avoid buckling.

Update Building Codes and Zoning

Requiring heat-minimizing designs, materials and landscaping for all new structures and renovations can promote cooling.
Adjusting zoning to prevent concentrated development and preserve open land can also help ease urban heat islands.

Incentivize Adaptations for Vulnerable Groups

Subsidy programs can fund building retrofits, air conditioning system upgrades, community cooling centers, resilient landscaping and more to alleviate heat impacts among lower-income residents.

Launch Public Awareness Campaigns

Widespread public education is vital for communicating heat risks and preventative actions residents can take to protect themselves during hot weather. Outreach can literally save lives by preventing heat stress.
Cities often utilize social media, text alerts, radio ads, billboards and community organizations to spread word of what to do before and during hot days.

What Role Can New Technologies Play?

In addition to traditional infrastructure upgrades and design changes, cities globally are beginning to explore innovative new technologies aimed at mitigating the impacts of extreme heat on urban neighborhoods.

Some of the most promising and futuristic-seeming pilots and proposals include:

Artificial Cloud Shields

Some scientists have proposed dispersing heat-reflecting salt particles or crystals via drones or aircraft to create artificial cloud cover lowering temperatures, similar to clouds naturally deflecting sunlight.
Small-scale experiments have demonstrated modest cooling potential. But many questions remain about environmental impacts, costs and feasibility.

Quantum Computing Enabled Hyperlocal Weather Forecasting

New quantum machine learning computing capabilities may soon provide real-time hyperlocal weather predictions allowing emergency planners to identify developing hotspots during heatwaves and intervene.
This could optimize the efficiency of targeted aid distribution when extreme heat exceeds thresholds in neighborhoods facing the highest vulnerability.

Climate-Controlled Macro Pods

Prototypes of human-scale “macro pods” employing advanced heat exchange materials and technologies can maintain interior temperatures between 22-25°C regardless of exterior conditions, providing instant cooling shelters.
If manufactured affordably at scale, these could be deployed as easily accessible public temperature Havens during heat emergencies.

Passive Radiative Cooling Structures

Advanced new building materials under development can cool structures passively by reflecting sunlight and emitting heat via radiation exchange with the sky instead of trapping terrestrial heat.
Widespread use of these materials could reduce waste heat from buildings helping ease urban heat islands alongside expanded green infrastructure.

Vehicle-Scale External AC Units

Researchers are exploring vehicle-mounted emergency external cooling units that could traverse neighborhoods providing targeted temperature relief by exchanging heat directly with residents via radiative pads once pulled over and deployed.
This could function as a form of hyperlocal cooling triage during extreme heat events in highest risk areas.

Key Takeaways

Addressing escalating extreme heat presents an urgent crisis for cities worldwide seeking to keep residents safe in coming years and decades. But research provides reason for hope that with sufficient preparation, adaptation interventions, strong policies, awareness, and potential technological innovations, cities can enhance livability even with hotter temperatures.

The core things experts recommend leadership focus on include:

Using advanced weather and climate models to conduct metro-wide extreme heat risk assessments and create targeted emergency plans
Expanding green infrastructure and efficiency standards to ease urban heat islands
Creating advanced warning systems and distributing emergency resources based on neighborhood vulnerability levels
Educating residents on precautions they can take and recognizing heat stress symptoms
Exploring supplemental new cooling technologies in extreme cases

Armed with greater understanding of both intensifying heat threats and emerging resilience strategies, cities can overcome uncertainties and ensure they remain habitable for all residents through proactive adaptation.