Even as the climate warms, the cold is becoming a deadlier threat to Americans. New research this month shows that cold-related deaths have significantly increased in the U.S. over the past two decades.
Researchers at Harvard Medical School conducted the study, which aimed to better count the deaths caused by cold temperatures in the U.S. They found that the country’s cold-related mortality rate has more than doubled since the late 1990s, with deaths especially increasing in recent years. Important risk factors for the rise in deaths likely include extreme weather events tied to climate change, homelessness, and social isolation, the researchers say.
Extreme temperatures on either end of the thermometer can be life-threatening. While recent research has shown that heat-related deaths have risen in recent decades, cold weather tends to be deadlier in general. A 2021 study found that the cold was responsible for about three-fourths of extreme temperature deaths worldwide in 2019, for instance (there were an estimated 1.7 million deaths overall that year).
The Harvard researchers note that cold-related deaths in the U.S. have been studied only minimally, and little is known about how this burden has changed over time. To address this knowledge gap, they analyzed death certificate data collected by the Centers for Disease Control and Prevention, focusing specifically on deaths where cold was recorded as either an underlying or contributing cause.
Between 1999 and 2022, there were just over 40,000 cold-related deaths in the U.S., the researchers found. After adjusting for age, they found that the mortality rate had risen from 0.44 cold-related deaths per 100,000 people in 1999 to 0.92 such deaths per 100,000 people in 2022. Much of this jump was the result of a significant annual increase in deaths between 2017 and 2022. The team’s findings were published this month in the journal JAMA.
“There has been a rightful focus on heat-related deaths given the undeniable nature of global warming,” lead study author Rishi Wadhera, a cardiologist and public health researcher at Harvard, told Gizmodo in an email. “However, our study findings serve as a striking reminder that cold-related deaths also remain an important public health issue.”
While their study isn’t designed to identify any specific reasons for this increase, Wadhera and his colleagues do highlight some possible factors.
Climate change is known to raise the risk of both hot and cold extreme weather events, for instance. But it’s also likely that more Americans today are at greater risk of being left out in the cold than before, particularly people with unstable living situations, Wadhera notes.
“For example, we know that the number of unsheltered people in the US has risen over the past several years—this is a population that is most exposed to outside weather, including cold snaps,” he said.
Levels of homelessness in the U.S. have generally increased since 2016 (the early years of the covid-19 pandemic were a notable exception, thanks in part to generous relief programs). In 2023, chronic homelessness surpassed record numbers set in 2007, when modern data collection efforts began, according to the Department of Housing and Urban Development (their report this year is not yet out). Substance use and social isolation may also increase people’s risk of being exposed to unsafe conditions, temperature included.
Certain trends emerged in the team’s data showing who was most vulnerable to cold-related deaths. Regionally, the mortality rate was highest in the Midwest, where winters can be especially brutal, for instance. The highest mortality rates across racial and ethnic groups was seen among Native and Black Americans, respectively, and the highest death rate age-wise was seen in people over 75.
The authors say that more research has to be done to unpack exactly why cold-related deaths have been increasing. At the same time, there are already steps that policymakers can and should take to prevent these tragic losses of life, such as making sure that vulnerable populations are living in homes with reliable indoor heating or expanding access to warming centers.
“Our findings should raise awareness that injury and death due to cold weather exposure is possible— especially for older populations who have more health conditions, unsheltered people who are most exposed to outside weather, and low-income populations who may not have access to adequate indoor heating,” Wadhera said.