On average, extreme heat over the past 30 years has killed more people in the United States than any other weather event, according to the U.S. Natural Hazard Statistics. That means more lives have been lost to heat over the past three decades than to hurricanes, floods, or tornadoes — and National Oceanic and Atmospheric Administration (NOAA) data shows that extremely hot days are growing in intensity and frequency while also stretching farther into the spring and autumn seasons. This has serious consequences for human health, especially for populations that already face grave inequities.
As hotter average temperatures become the new normal, Black, Latino, and American Indian and Alaska Native (AIAN) communities suffer disproportionately. This is a historical trend that will be amplified by climate change, says Vivek Shandas, a professor of climate adaptation at Portland State University.
According to June Spector, MD, MPH, director of occupational and environmental medicine at the University of Washington, many factors are to blame. “As with a lot of health outcomes, the systems and structures are really where we need to focus. For example, if we have a lot of Latinx folks working in agriculture, there's also a rural aspect to it since there is less access to health services in rural areas. There are also issues around how folks are paid, and poverty aspects that come into play, as well as discrimination, power structures, and harassment,” says Dr. Spector. “These compound the disproportionate effects that these communities face.”
What Heat Does to the Body
While the Centers for Disease Control and Prevention (CDC) estimates that heat kills an average of roughly 700 Americans a year, research shows that heat likely plays a role in far more deaths in the United States. A study?published in June 2020 in the journal Environmental Epidemiology?determined that heat was a contributing factor in 5,600 deaths every year between 1997 and 2006. Moderate, rather than extreme heat, contributed to most of these deaths, but Spector says that’s because humans are able to acclimate to hot weather if they live in traditionally hot places. What is hot in Phoenix is not the same as what is considered hot in Minneapolis. In addition, humidity and wind also play an important role in how heat affects people.
“With weather, we have to think about humidity, because the way humans cool down is through evaporative cooling, or sweat,” says Spector. When the air is already full of moisture, less sweat can evaporate. Wind also helps bodies cool off, she says.
According to Spector, certain medications can inhibit a person’s ability to sweat or increase their metabolism, making their core temperature warmer. Heat illnesses are common when temperatures soar, and heat stroke, the most serious heat illness, can quickly become fatal or cause lasting organ damage, according to the CDC. In addition, once a person experiences a heat illness, they are more prone to experiencing them again, says Spector.
When this cycle of heat and dehydration gets repeated, over a summer season, for example, it can cause acute kidney injury, according to Spector. “There are gaps in the literature as far as long-term exposure to heat, but there is a lot of speculation that if we are seeing certain health outcomes over a short period of time, that these could cumulatively be a problem,” she says.
People with preexisting conditions, including heart disease and diabetes, as well as pregnant women, also have a higher risk of being injured or dying due to heat exposure.
According to the CDC, 41 percent of Americans who died from heat-related causes had an underlying condition that was the primary cause of death (the heat was listed as a contributing factor). Of those deaths, the report found that 49 percent were due to major cardiovascular disease. Exposure to heat has also been tied to poorer mental health outcomes, including an increased rate of suicide, as shown by a meta-analysis of 35 studies?published in August 2018 in the journal Public Health.
Heat Exasperates Health Inequities
Largely due to generations of racist systems that have created stark health inequities in the United States, which include less access to healthy food, healthy living conditions, and health care, Black communities already suffer from hypertension and heart disease at higher rates, says Adrienne Hollis, senior climate justice and health scientist at the Union of Concerned Scientists (UCS). According to the Office of Minority Health (OMH), Black American adults are 40 percent more likely to have high blood pressure and are 20 percent more likely to die of heart disease than white Americans. This puts them at a higher risk for heat-related injury or death.
Lack of insurance also plays a key role in who is killed or injured by heat exposure, says Juan Declet-Barreto, a climate vulnerability social scientist at UCS. In 2018, nearly 27 percent of Hispanic Americans and more than 15 percent of Black Americans lacked health insurance, compared with 9 percent of white Americans and 8 percent of Asian Americans, according to the National Center for Health Statistics.
“We know that Latin American people in this country have less access to job benefits like sick days and health care, which leaves them less able to deal with preexisting conditions that are exacerbated by heat,” says Declet-Barreto. “Occupationally, Latinx people are more likely to work outdoor jobs which exposes them to more extreme heat and other conditions than other people, and many are undocumented.”
According to the United States Department of Agriculture (USDA), nearly 60 percent of farm laborers in the United States are Latinos, and roughly half of all farm laborers are not legal citizens of the United States. A study published in April 2018 in the American Journal of Public Health?estimated that non-U.S. citizens age 18 to 24 were 20 times more likely to die from excessive heat exposure than were U.S. citizens. Twenty percent reported being exposed to heat on a farm.
Declet-Barreto says that not being a legal citizen is usually a barrier to getting both medical care and fair wages that can help people afford things like air-conditioned vehicles and homes. Regardless of citizenship status, “the profile of a Latin American immigrant is low income, and 70 percent reside in cities, where they typically live in the poorest parts of the city, in housing that is substandard or not energy efficient and that may not have AC,” says Declet-Barreto.
According to the most recent CDC statistics, between 2004 and 2018, AIAN populations had the highest rates of heat-related deaths, double the rate of non-Hispanic Black Americans, who had the second-highest rates.
Linda Bane Frizzell, PhD, an associate professor at the University of Minnesota School of Public Health, who is a member of the Eastern Band of Cherokee Indians and Lakota and? a board member of the The Indian Health Board of Minneapolis, says Indian Health Service (IHS) — an agency within the U.S. Department of Health and Human Services that is responsible for providing federal health services to AIAN communities — is crucially underfunded. According to the OMH, 60 percent of AIAN people live in rural areas, the highest of any race or ethnic group.
“American Indians can go anywhere [for medical care], but in rural America, health clinics are closing. Access is a big deal,” says Frizzell, noting that it can take 30 minutes or more for an ambulance to arrive to a person in need who lives on a reservation.
Urban Heat Islands and the Lasting Effects of Redlined Neighborhoods
In cities, racist policies and urban planning from decades ago have resulted in many Black Americans living in neighborhoods that are hotter by design. A study published in January 2020 in the journal Climate?looked at summer temperatures in 108 American cities. Researchers found that even when an entire city was hit with a heat wave, there was a pattern of certain neighborhoods being much hotter — and deadlier — than others. These neighborhoods were redlined, meaning developers and urban planners drew lines around Black neighborhoods on residential maps. Until 1968, lenders could legally refuse to issue mortgages to people who lived in these neighborhoods. As a result, these areas lack critical infrastructure that keeps historically white neighborhoods cooler, things like parks and tree cover. In Portland, Oregon, and Denver, the two cities with the highest heat disparities, redlined neighborhoods were 12 degrees hotter than the rest of the city.
“It is increasingly becoming clear that actions, plans, and policies that were carried out 100 years ago are well and alive today, and that they disproportionately affect Black and Brown communities’ health and well-being and ability to get basic necessities,” says Shandas.
According to Hollis, redlining forced Black Americans into less desirable neighborhoods, often low-lying areas that, because of flooding, won’t support tree growth. According to a study published in April 2019 in the journal PNAS, adequate tree canopy coverage can cool a neighborhood in the summer by 10 degrees. In turn, tree cover actually reduces air-conditioning demand and lowers energy costs for residents, according to the Environmental Protection Agency (EPA).
There’s another factor raising temperatures in certain areas of cities. “How much of a neighborhood is covered by impermeable surfaces like asphalt, vertical services like buildings, and highways that bring heat-trapping exhaust impacts how hot parts of a city get,” says Declet-Barreto, noting that packing a neighborhood full of tall buildings and asphalt and very little green space creates an urban heat island, in which parts of a city do not cool off at night when external temperatures drop.
“Heat correlates with a lot of different potential health outcomes and it depends on people’s access to cooling,” says Spector, noting that people in low-income redlined neighborhoods may need to choose between running an AC unit and paying for another necessity.
The UCS Killer Heat in the United States report, published in July 2019, showed that counties with large Black populations experience extreme heat two to three more days per year than counties with smaller Black populations. By midcentury, this is expected to jump to about 20 more days annually. “We know that these impacts are here and that they will continue to get worse,” says Declet-Barreto. In the end, he says the road to closing the racial heat divide will take years of legislative action. According to Shandas, grassroots efforts are needed immediately.
This is something city governments are aware of and, in some cases, trying to change. The city of Denver is attempting to?improve the amount of greenery in poorer neighborhoods?— building new parks, planting trees, and improving existing spaces — but it’s not happening as quickly or as smoothly as officials would like. The slow pace of urban planning and concerns by residents about possible gentrification show this problem isn’t always an easy one to fix.
“It’s imperative to build trust and engage people who have experienced trauma by what policies and planning has done to these communities,” says Shandas.