PHOENIX — By 10 p.m., the temperature outside was still above 100°F.
Emergency rooms across Arizona were already treating waves of heat-related illnesses when parts of the local electrical grid began to strain under surging demand. Air conditioners ran nonstop. Transformers overheated. Utility crews moved from neighborhood to neighborhood responding to outage calls as thousands of residents searched for relief in one of the hottest urban regions in the United States.
For many families, losing electricity was no longer an inconvenience. It was a direct threat to survival.
Residents described apartments becoming dangerously hot within hours of losing power.
“We had nowhere to go once the apartment started heating up,” said Maria Gonzalez, a Phoenix resident who lost electricity during last summer’s heatwave. “By midnight it still felt like an oven inside.”
Emergency crews eventually restored service, but public-health officials warned that longer outages during future heatwaves could become far more dangerous.
“In extreme heat, a power outage becomes a public-health emergency very quickly,” said Dr. Jennifer Vanos, a climate and health researcher at Arizona State University. “The human body needs time to cool overnight. Without that recovery period, the risks rise dramatically.”
That warning is becoming increasingly relevant far beyond the American Southwest.
Climate scientists, grid operators, and emergency planners are raising concerns that prolonged heatwaves could push aging power systems beyond their limits at the exact moment populations are becoming more dependent on air conditioning to stay alive. In cities already experiencing record temperatures, electricity demand is climbing faster than many grids were designed to handle.
The International Energy Agency estimates the world could add nearly 5 billion air conditioners by 2050 as rising temperatures and urbanization reshape energy demand globally. At the same time, more than 40 countries representing nearly 70% of global electricity demand set new peak demand records during major heat events in 2024.
For policymakers and emergency planners, the concern extends well beyond uncomfortable temperatures.
Heatwaves Are Becoming Grid Emergencies
Utilities have dealt with summer demand spikes for decades. What worries planners now is how quickly those spikes are growing.
When temperatures surge, millions of households and businesses switch on cooling systems simultaneously. Utilities respond by pushing more electricity through transmission lines, transformers, and substations—many of which were built decades ago under very different climate assumptions.
But heat also weakens the infrastructure itself.
Transmission lines become less efficient in extreme temperatures. Transformers overheat more easily. Gas-fired power plants can lose efficiency during prolonged heatwaves. In some cases, drought conditions linked to climate change also reduce hydropower generation precisely when electricity demand surges.
In Phoenix, utility officials urged residents to conserve electricity during peak evening hours, when air conditioners continue running long after sunset because buildings retain heat deep into the night.
In some neighborhoods, crews responding to transformer failures worked overnight as asphalt temperatures remained dangerously high even after dark.
Utilities in several countries are now facing demand spikes they were never designed to manage.
India experienced some of its highest-ever electricity demand during the severe 2024 heat season, with cooling demand playing a major role. According to energy think tank Ember, electricity consumption in India rose sharply during heatwave months as temperatures crossed dangerous thresholds in multiple states.
In the Philippines, officials issued repeated red alerts over grid instability during extreme heat this year, warning residents about rotating blackouts as electricity demand climbed. Some areas experienced outages lasting several hours during periods of dangerous temperatures.
“This is no longer a future climate scenario,” said one regional grid analyst interviewed by Reuters during the outages. “Demand patterns are changing faster than infrastructure upgrades.”
When Cooling Becomes Essential
In many major cities, public-health officials now treat access to cooling the same way they treat access to clean water or emergency medical care.
According to the World Health Organization, heat kills hundreds of thousands of people globally each year, with the elderly, low-income households, outdoor workers, and people with preexisting health conditions facing the greatest risks. Urban heat islands—dense areas filled with asphalt, concrete, and limited tree cover—can trap heat overnight, preventing buildings from cooling after sunset.
During the 2023 heatwave in Arizona, nighttime temperatures in some neighborhoods remained above 95°F. Public-health experts warned that prolonged exposure to those conditions without access to cooling could become life-threatening, particularly for older adults living alone.
Demand for cooling is rising across many cities just as heatwaves are becoming longer and overnight temperatures remain dangerously high.
A 2024 study examining extreme heat and power outages found that blackout-related mortality risks rise significantly during severe heat events because residents lose access not only to air conditioning, but also refrigeration, medical equipment, elevators, communications systems, and emergency services.
Hospitals face additional pressure during these periods.
Emergency departments typically experience spikes in admissions during major heatwaves, while backup generators and cooling systems operate under intense strain. In some cities, public cooling centers have become as important during summer emergencies as storm shelters are during hurricanes.
Aging Infrastructure Is Colliding With a Hotter Climate
Many electrical grids across the world were not built for prolonged extreme heat.
The North American Electric Reliability Corporation warned in a recent assessment that large parts of the United States face elevated risks of electricity shortfalls over the coming decade due to rising demand, retiring power plants, and delays in transmission expansion.
The challenge extends far beyond North America.
Rapid urbanization across Asia, the Middle East, and parts of Africa is dramatically increasing cooling demand. Yet many growing cities still struggle with aging transmission systems, limited reserve capacity, and uneven access to reliable electricity.
The International Energy Agency warns that without major improvements in energy efficiency and grid modernization, cooling demand alone could become one of the largest drivers of global electricity growth in coming decades)
Emergency officials say the deeper concern is what happens when several systems begin failing at once during prolonged heat.
Power outages can disrupt hospitals, water distribution, communications networks, elevators, and emergency transportation systems simultaneously. In dense urban regions, those cascading failures can quickly overwhelm local response capacity.
What Cities Are Starting to Do
Some cities are already adapting.
Phoenix has expanded public cooling centers and hydration stations during extreme heat alerts. Parts of California are investing heavily in battery storage systems designed to stabilize the grid during peak summer demand. In Singapore, urban planners are integrating reflective materials, green corridors, and passive cooling designs into long-term city planning.
Energy experts say those efforts will likely become more common.
The National Renewable Energy Laboratory reported that expanded solar generation and battery storage helped parts of the U.S. grid maintain stability during periods of intense summer demand in 2024.
Policy specialists increasingly recommend several priorities:
- upgrading aging transmission infrastructure
- expanding battery storage and renewable energy
- improving building insulation and efficiency
- creating neighborhood cooling hubs
- strengthening blackout-response protocols
- prioritizing vulnerable communities during emergencies
Some experts also argue that cities need to rethink how they classify heat disasters altogether.
“We prepare extensively for hurricanes, floods, and earthquakes,” said climate adaptation researcher Kristina Dahl in a recent public policy discussion. “But extreme heat is often treated as invisible, even though it kills more people in many regions.”
A Warning About the Future of Urban Survival
Officials and grid operators say the deeper concern is not simply rising temperatures, but the growing pressure on interconnected systems that modern cities depend on every day.
Electricity demand for cooling continues to climb across major urban regions as heatwaves grow longer and overnight temperatures remain elevated. At the same time, aging infrastructure in many countries is already operating close to capacity during peak summer months.
When outages happen during extreme heat, the consequences move quickly beyond inconvenience.
For decades, electricity has been treated as background infrastructure—reliable, constant, almost invisible. Climate change is beginning to challenge that assumption.
In some of the world’s hottest cities, officials are increasingly preparing for a future where keeping the power on during extreme heat could become a matter of public safety.