The Heat Is On

Because of climate change, this summer threatens to be a scorcher. It’s time to adapt.

By Osha Gray Davidson

June 21, 2023

Double exposure portrait of young fitness Woman hand wiping sweat and summer heat wave concept.

Illustration by Tomwang112/iStock

In a short video captured last summer, a UPS delivery worker in metro Phoenix, Arizona, is seen collapsing on someone’s doorstep in 109°F heat. Twenty seconds later, he struggles to get up. Still unsteady on his feet, he manages to ring the doorbell and then, delivery complete, slowly weaves his way back toward the street, his image shimmering and then disappearing into the blinding sunlight.

In addition to eliciting horror, the video, which has more than 20 million views on YouTube, likely caused many viewers to give thanks that they don’t live in Phoenix, the United States’ hottest large city.

But a recent study by climate scientists should give pause to people living outside the desert southwest.

Writing in the journal Nature Sustainability, a team of researchers led by the University of Exeter’s Global Systems Institute determined that as early as 2080, rising temperatures caused by the burning of coal, oil, and gas will place as much as a third of the global population outside the “human climate niche,” the environment in which most humans have lived since prehistory. A separate report by the World Meteorological Organization found that within just five years, there’s a 66 percent chance that the average global temperature will be 2.7°F above preindustrial levels—that is, above the ceiling the 2015 Paris Agreement hoped to prevent. This temperature exceedance isn’t necessarily permanent, WMO secretary-general Petteri Taalas said. “However, [we’re] sounding the alarm that we will breach the 1.5°C [2.7°F] level on a temporary basis with increasing frequency.”

Scientists warn that permanently crossing that temperature threshold could have a domino effect on several irreversible climate trigger points. These include the melting of the Greenland ice sheet, which would raise sea level by 20 feet and disrupt ocean currents around the world, leading to a die-off of phytoplankton, a plantlike organism that removes up to 30 percent of the CO2 emitted by humans.

The scope of the problem is dire, but the basic fact of rapidly rising temperatures shouldn’t surprise anyone who’s been paying attention.


Noting this pattern of record-shattering temperatures is important, but it’s the lived experience of a large and growing portion of humanity that will force change.

The silent killer

Already, heat kills more people each year than any other weather disaster, including nearly twice as many fatalities as floods, and more than hurricanes, tornadoes, and cold weather combined. But because deadly extreme heat events leave no obvious path of physical destruction, they rarely receive media attention. That’s why experts like Ladd Keith often refer to heat as the “silent killer.”

“Heat has largely been ignored by the media, the public, and the government,” Keith, a professor of planning and sustainable built environments at the University of Arizona, told Sierra. “Which explains why we have very little national legislation that targets heat.” Keith points out that deadly extreme heat events don’t qualify for federal disaster assistance, let alone federal efforts to prevent these deaths.

“Hurricane Katrina tragically killed 1,800 people in New Orleans,” Keith said. “There was a massive federal policy change to make sure that we avoided another situation like that.” No such action followed the 2021 Pacific Northwest heat wave that killed more than 1,400 people in the United States and Canada, he said.

A lethal combination

Experts predict that the next two summers will likely be among the hottest on record—and not just because of anthropogenic climate change. The oceanic climate pattern known as ENSO (El Niño–Southern Oscillation) affects global weather worldwide. In the El Niño cycle, an enormous volume of water in the Pacific Ocean heats up. Scientists expect an unusually strong El Niño this year, and we may already be witnessing its effects. Researchers at the National Oceanic and Atmospheric Administration (NOAA) determined that global ocean temperatures in April were the highest on record for that month—and just 2/100 of a degree Fahrenheit below the record for any month ever.

In the United States, El Niño is likely to send temperatures soaring across a wide swath of central states this summer. The summer following an El Niño winter is generally even hotter, meaning that deadly heat waves are even more likely across the globe, including in the US, next summer.

The adaptation imperative 

According to the United Nations’ Intergovernmental Panel on Climate Change, the primary action needed to prevent catastrophic heat waves in the long term is a drastic and immediate reduction in carbon pollution and methane emissions. These measures include electrifying transportation, replacing coal and methane gas power stations with renewable power sources like solar and wind, and decarbonizing cement, steel, and plastics.

But even if all carbon pollution were eliminated tomorrow, temperatures would remain high for years because of the enormous quantity of greenhouse gases already trapped in the planet’s atmosphere and the fact that CO2 will remain there for between 300 and 1,000 years.

Because of this, experts now stress the need to adapt to our already hot world, a task, they say, that is difficult but possible.

“Most heat-related deaths are preventable,” Portland State University professor Vivek Shandas told a congressional committee after the 2021 heat wave killed an estimated 600 people in Oregon and Washington. Reducing deaths from heat, he said, will require a multipronged effort between federal agencies, including the Centers for Disease Control, NOAA, the Federal Emergency Management Agency (FEMA), and the EPA. “The need for coordination has never been greater,” Shandas stressed.

This is especially true for cities, which are often hotter than surrounding areas because of what’s known as the “urban heat island” effect. Most US cities have destroyed the natural vegetation and bodies of water that help cool the air. Instead, the urban environment is paved over and built up, using materials that, rather than reflecting sunlight, absorb its heat, which is released at night so that cities don’t cool off even when the sun is down. Factor in the tall buildings that block cooling winds and the heat generated by air-conditioners and by cars and trucks that burn petroleum, and the result is cities that are up to 7°F hotter than the surrounding areas.

(Rural areas present their own challenges, especially in southeastern states, where simultaneous high temperatures and humidity can reach extreme levels. In rural North Carolina, for example, heat illness rates are 10 times higher than in urban areas.)

Phoenix mayor Kate Gallego recently called on the Biden administration to take a first federal step toward solving the problem by adding extreme heat to FEMA’s list of declared disasters. “Resources from pop-up shelters to additional outreach to our vulnerable residents could help us successfully navigate unforgiving summers,” Gallego said.

Gallego’s mention of “vulnerable residents” highlights a key to saving lives and is the reason Shandra refers to heat as not just a silent killer but a discriminating one.

The best-known vulnerability to heat is age. As we grow older our bodies are less able to adjust to changes in temperature. That explains why the average age of people who died in the Portland, Oregon, area during the 2021 “heat dome” event was 70 years old.

Because of our long history of racial discrimination in housing and city services, Shandra said, Black and brown communities are more likely to be located in “hot zones”—that is, areas without shade or other cooling mechanisms. During the deadly Pacific Northwest heat wave, Shandas collected temperature data across Portland. He found that temperatures were as much as 25 degrees hotter in poorer neighborhoods than in more affluent ones.

The patchwork nature of hotter and cooler neighborhoods within cities has led researchers like Lynée Turek-Hankins at the University of Miami to replace the term “heat island” with a more nuanced one: “urban heat archipelago.”

“In a wealthy Miami neighborhood you have a really wonderful, strong, dense urban canopy,” Turek-Hankins said. “In contrast, we also have low-income communities with no canopy and with lots of black asphalt. It’s not hard to imagine, if you’re standing on the sidewalks, which one is going to be hotter and which is going be cooler.” 

University of Arizona urban planner Ladd Keith stressed that “equity is a huge component of urban heat resilience,” adding that “marginalized populations are less able to cope with rising temperatures.”

The nexus of race, poverty, and official indifference results in less access to medical care, air conditioning, and housing with adequate insulation. “Every aspect of what we work on related to urban heat resilience should focus on these most vulnerable populations,” Keith said.

But so far, that has rarely happened, even in cities that are implementing heat mitigation measures.

A study Keith recently led analyzed how heat mitigation plans and policies are linked to the location of vulnerable communities in Baltimore, Boston, Fort Lauderdale, Seattle, and Houston. The results, he said, were sobering:

“Out of all of those cities, only Boston was really targeting lower-income, marginalized populations and the hotter neighborhoods,” he said. “In the other cities, there was no correlation between heat mitigation policies and vulnerable people and neighborhoods.”

Working in the heat

The video of the UPS worker collapsing in the heat points to another important risk factor for heat illness and death: whether you work inside or outside. One study found that 80 percent of heat-related fatalities were among outdoor workers, with the level of risk varying dramatically by job type. Farmworkers, for example, are at least 35 times more likely to die from heat than are workers in all other industries combined. Construction ranks number two, with an estimated 13 times the overall mortality rate from high temperatures. Environmental justice is an issue here as well, because Black and brown workers are overrepresented in these dangerous sectors.

Most of these deaths are preventable, Juley Fulcher, a health and safety advocate for the group Public Citizen, told Sierra.

“The problem,” Fulcher said, “is that the government agency responsible for worker safety, the Occupational Safety and Health Administration (OSHA), which has rules regulating so many workplace hazards, doesn’t have a single one targeting exposure to heat.”

Public Citizen is trying to change that. In 2018, the group launched a campaign petitioning OSHA to create a heat-stress standard to protect workers. (The Sierra Club was one of the petitioners.)

The proposal was ignored by the Trump administration. Early in the Biden administration, OSHA began work on just such a standard, and while Fulcher welcomes the action, the process takes seven to eight years to implement.

“Workers simply can’t wait,” she said. “Summers are getting hotter. Heat waves are happening more frequently, growing more intense, lasting longer, and happening to areas that haven’t seen them before. So now our efforts are to get legislation passed that would allow OSHA to issue an interim heat rule.”

In addition to protecting workers now, an interim rule could save lives well into the future, even if OSHA doesn’t have a final regulation in place before an administration hostile to protecting workers replaces the current one. “An interim rule doesn’t expire,” Fulcher said. “It remains in effect until a final one is developed.” 

Ladd Keith is upbeat about our ability to protect all Americans from extreme heat—if we take an equitable approach. Beyond our borders, however, he has his doubts.

“The scenarios that keep me up at night are lower-income nations in the Global South. Entire populations may be exposed to extreme heat events where there’s absolutely no capacity for those populations to have cooling centers, or even the electrical capacity to kind of make it through. That’s my nightmare scenario, for sure.”