Cold kills more Americans each year, study finds

Even as the climate warms, the cold has become a deadly threat to Americans. New research this month shows that cold-related deaths have increased significantly in the United States over the past two decades.

Harvard Medical School researchers conducted the study, which aims to better count deaths caused by cold temperatures in the United States. They discovered that the country’s cold death rate has more than doubled since the end of the 1990s, with deaths especially increasing in recent years. Important risk factors for the increase in deaths likely include extreme weather events linked to climate change, homelessness and social isolation, the researchers say.

Extreme temperatures at either end of the thermometer can be life-threatening. While recent research has shown that heat-related deaths have increased in recent decades, cold weather tends to be deadlier overall. A 2021 study found that the cold was responsible for about three-quarters of the deaths from extreme temperatures in the world in 2019, for example (there were an estimated 1.7 million deaths in the whole of that year).

Harvard researchers note that cold-related deaths in the United States 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 the cold was recorded as an underlying or contributing cause.

Between 1999 and 2022, there were just over 40,000 cold-related deaths in the United States, the researchers found. After adjusting for age, they found that the death rate had risen from 0.44 deaths per 100,000 people in 1999 to 0.92 deaths per 100,000 people in 2022. Much of this jump is the result of a significant annual increase in deaths between 2017. and 2022. The results of the team were published this month in the newspaper JAMA.

“There has been a fair amount of focus on heat-related deaths given the undeniable nature of global warming,” study lead author Rishi Wadhera, a cardiologist and public health researcher at Harvard, told Gizmodo in an email. “However, our study results serve as a striking reminder that cold-related deaths still remain an important public health problem.”

While their study is not designed to identify any specific reason for this increase, Wadhera and his colleagues highlight some possible factors.

Climate change is known to raise the risk of heat and extreme cold weather eventsfor example. But it’s also likely that more Americans today are at greater risk of being left out in the cold than before, especially people with unstable living situations, Wadhera notes.

“For example, we know that the number of people without shelter in the United States has grown in recent years – this is a population that is more exposed to the external climate, including the cold,” he said.

Homelessness levels in the US have generally increased since 2016 (the early years of the covid-19 pandemic were a notable exceptionsthanks in part to generous relief programs). In 2023, chronically homeless overcome record numbers set in 2007, when modern data collection efforts began, according to the Department of Housing and Urban Development (its report this year is not yet out). Substance use and social isolation can also increase people’s risk of being exposed to unsafe conditions, including temperature.

Certain trends emerged in the team’s data showing who was most vulnerable to cold-related deaths. At the regional level, the mortality rate was higher in the Midwest, where winters can be particularly brutal, for example. The highest death rates among racial and ethnic groups were seen among Native Americans and Blacks, respectively, and the highest death rate by age was seen in people over 75 years of age.

The authors say more research needs to be done to unravel exactly why cold-related deaths have increased. At the same time, there are already steps that policymakers can and should take to prevent these tragic losses of life, such as ensuring that vulnerable populations live in homes with reliable indoor heating or expanding access to warming centers .

“Our findings should raise awareness that injury and death from exposure to cold weather is possible — especially for older populations who have more health conditions, homeless people who are more exposed to the weather outside, and the low-income populations that do not have access to adequate indoor heating,” said Wadhera.