Anna Moneymaker/Getty Images

When Hurricane Ida battered Louisiana with catastrophic flooding and powerful winds in August 2021, more than 1 million people lost power. Then came the heat wave. Temperatures rose above 90 degrees Fahrenheit — a sucker punch to those sweltering in their homes, unable to turn on air conditioning as power outages stretched on for days.

It was the heat that proved deadliest in New Orleans, responsible for at least nine of the city’s 14 hurricane-related deaths.

The combination of a hurricane, heat wave and a multi-day power outage is a nightmare scenario, but it’s one set to become more common as humans continue to warm the planet, fueling devastating extreme weather. And it reveals an uncomfortable truth about the vulnerability of humanity’s ultimate protection against heat: Air conditioning.

Air conditioning is far from perfect. It gobbles up energy, most of which still comes from planet-heating fossil fuels, meaning it exacerbates the very problem it’s used to mitigate. Plus, it’s only available to those who can afford it, further widening social inequality.

But it is also a lifeline against increasingly brutal heat, the deadliest type of extreme weather. It allows people to live in places where temperatures push close to the limits of survivability and where extreme heat persists even at night.

Demand for AC is exploding, expected to triple worldwide by 2050, as global temperatures soar and incomes grow.

The problem is, without electricity, access to air conditioning is lost. And many electrical grids are being pushed to a breaking point due to increasingly frequent extreme weather and soaring demand for cooling.

Weather accounted for 80% of major power outages across the US between 2000 and 2023, according to a report from Climate Central, a nonprofit research group. “Every aspect of weather is beating on the already vulnerable grid and really giving it a test,” said Jen Brady, a senior data analyst at Climate Central.

In the US, the aging grid was designed “for the weather of the past, rather than the weather of the future,” said Michael Webber, a professor in mechanical engineering at the University of Texas at Austin.

The main threat is storms, which can bring down transmission wires and poles. But heat, too, is having an impact. If it’s really hot, the system works less efficiently. Webber compares it to how someone might feel running a marathon in the heat — “we just kind of break down.” The grid can also buckle under the weight of demand as everyone cranks up their AC at the same time to cope with high temperatures.

The number of major outages in the US — affecting more than 50,000 customers and lasting at least an hour — doubled between 2017 and 2020, said Brian Stone Jr., a professor specializing in urban environmental planning and design at the Georgia Institute of Technology. “Most of the increase is happening during the summer months, that tells me that these systems are not resilient,” he told CNN.

Surging demand for cooling during an August 2020 heat wave in California prompted the state’s main grid operator to cut power to hundreds of thousands of homes in rolling blackouts for the first time in 20 years.

In 2021, during the blistering heat wave that scorched the Pacific Northwest, power equipment buckled in the heat, triggering rolling blackouts for tens of thousands as temperatures soared above 100 degrees Fahrenheit.

It is not just the US that is struggling. In June, when temperatures in southern Europe topped 104 degrees Fahrenheit, parts of Albania, Bosnia, Croatia and Montenegro experienced hours-long blackouts as demand for electricity spiked.

People waiting in extreme heat to buy ice at Duplantier Ice Service in New Orleans, Louisiana on September 1, 2021, as power remained out in most of the city after Hurricane Ida ripped through the state. Leah Millis/Reuters

Even short power outages can be dangerous. “If the grid goes out while there’s a heat wave, it goes from uncomfortable to deadly pretty quickly,” Webber said.

Heat can affect vital organs and cause heat exhaustion, heat stroke and even death. If the power goes out when it’s very cold, people can add layers, make fires and huddle together. “If it gets really hot, there’s only one way to cool, and that is with electricity,” Webber said.

The combination of a heat wave and power outages “is the most deadly climate-related event we can imagine,” said Stone.

He and a team of scientists explored the potential impacts of a heat wave coinciding with a multi-day outage caused by extreme weather or a cyberattack. Focusing on Atlanta, Detroit and Phoenix, they looked at exposure inside people’s homes, a major driver of heat-related illness during a power outage.

The figures were particularly stark for Phoenix. During a three to four-day heat event and outage, half the city’s population — nearly 800,000 people — would require hospital treatment for heat-related illnesses, according to the findings. More than 13,000 would die.

A power outage in Phoenix causes a “very dramatic shift in heat illness,” Stone said, because the city’s climate is so extreme and people struggle to adapt. In an unfortunate irony, widespread air conditioning may actually make residents less resilient because they are so acclimatized to cooling in their homes and workplaces, Stone said.

Authorities in Phoenix say the city is well prepared. Kate Gallego, the city’s mayor, said Stone’s research was based on an extremely unlikely scenario. “The study does not account for any of the existing emergency response plans in place, or the fact that our electric grid consistently ranks among the most reliable in the country,” Gallego told CNN.

Arizona Public Service, one of the energy companies providing power in Phoenix, said it has robust plans in place to prevent large-scale interruptions and regularly maintains the grid.

But while the chances of a combined multi-day power outage and heat wave in Phoenix may be low, Stone said, it’s still possible and becoming more likely as the climate crisis worsens.

A man drinking water in his tent in “the Zone,” the largest homeless encampment in Phoenix, Arizona, during the city’s worst heat wave on record, on July 25, 2023. 

Mario Tama/Getty Images

Drastically cutting planet-heating pollution is the best long-term defense against heat and extreme weather, but the world is already committed to several decades of rising temperatures, Stone said.

In the shorter-term, there are ways to limit vulnerabilities.

Making the grid more robust and resilient is one, Stone said. This includes repairs and upgrades that take into account the climate of the future. Expanding and modernizing the grid, including adding more power plants and ensuring a diverse range of energy sources, will help strengthen it too, Webber said.

“But we also need to acknowledge that those grids will fail, and they are failing with greater rate of frequency, and so we need to have back-up plans,” Stone said.

That means rethinking cities, where heat-trapping concrete, steel and asphalt have replaced trees. Designing urban areas to be greener and cooler “can really increase grid resilience without investing in the grid itself,” he said.

Climate Central’s Brady pointed to community solar projects, which can keep local power on when the grid goes down. Babcock Ranch in Florida — “America’s first solar-powered town” — managed to keep the lights on in 2022 when Hurricane Ian barreled through, unlike nearby towns.

Making homes more efficient will also help, Webber said. Homes better adapted to extreme weather can help reduce electricity demand when temperatures soar.

Ultimately, “we’re vulnerable because we’ve built our lives around conditioned air,” Webber said, living in places where life would be impossible without it. The stress extreme weather is putting on the grid shows “climate change is here and we need to be dealing with it.”