Print and digital media headlines around the world tell the story of this summer’s persistent heat dome spanning large parts of the US, Europe and Asia. Excessive heat can be very dangerous to human health. It can lead to potentially fatal conditions such as heat exhaustion, which represents an acute loss of water and salt through profuse sweating. It can also cause heat stroke, which occurs when the body’s temperature rises so quickly and so much that the cooling system stops working completely and sweating is reduced as a result.
But for the most vulnerable populations, the effects of the heat are less clear. Heat is usually seen as a silent killer. It is only weeks or months later when researchers examine mortality data that they notice sharp increases in additional deaths after prolonged heat waves. More than 61,000 such deaths occurred in Europe last summer.
Between 2000 and 2019, annual deaths from heat exposure increased worldwide. The 20-year period coincided with the world warming by about 0.9 degrees Fahrenheit. Heat-related deaths have had a disproportionate impact in Asia, Africa, and southern Europe and North America.
Some of the people most at risk of heat-related death are people with cardiovascular disease, such as high blood pressure. Extreme heat puts pressure on the heart. Others may have respiratory or kidney problems.
Most deaths occur among the elderly, as they do not tend to cope as well with the heat imbalance. In other words, it is more difficult for their body to regulate temperature when they are exposed to intense heat.
Exposure to Extreme Cold is Deadlier
According to a 2021 study published in The Lancet Planetary Healthit is very cold more deadly. For every heat-related death, nine are cold-related.
Excessive cold can worsen existing medical conditions such as cardiovascular and respiratory diseases. For example, death rates from myocardial infarction increase as the temperature drops. This seems to indicate the way cold can affect blood circulation. People exposed to extremely cold conditions can also suffer from direct effects such as frostbite and potentially fatal hypothermia.
Interestingly enough, during the 2000-2019 period examined in the study, while heat-related deaths rose, deaths from cold exposure fell. And they decreased by more than the increase in heat-related deaths. Overall, the researchers estimated that around 650,000 fewer people worldwide died from heat exposure during the period 2000-2019 than in the 1980s and 1990s.
To illustrate just how big the difference was between cold and heat-related deaths, looking specifically at England and Wales, there were almost 800 heat-related deaths on average and 60,500 cold-related deaths between 2000 and 2019, according to the authors. Lancet publication.
Strangely enough, US data show no such stark contrast. Additionally, the two US government agencies that track heat and cold deaths—the National Oceanic and Atmospheric Administration (NOAA) and the Centers for Disease Control and Prevention (CDC)—are diametrically opposed to their estimates.
NOAA’s tally of what it calls “weather-related deaths” indicates that there were an average of 134 heat-related deaths per year during the 30-year period 1988 to 2017, and 30 cold-related deaths per year.
Unlike NOAA, the CDC’s National Center for Health Statistics’ Compressed Mortality Database, which is based on actual death certificates, indicates that about twice as many people die from colds in any given year as from heat.
Still, the CDC’s calculations are far from the kinds of numbers published in the Lancet study, for England and Wales and the world as a whole.
This is not the first time that organizations’ estimates of the same observable events would be far from each other. There are inconsistencies in the definitions and measurement assumptions underlying each organization’s calculation of cold- and heat-related deaths.
Perhaps another way to approximate the relative difference in cold and heat related deaths is to compare deaths in winter and non-winter months. In the US, death rates tended to be higher in the winter months 8% to 12% higher than in non-winter months. Although this can be attributed to the effects of the common cold it is also partly a function of the greater prevalence of respiratory illnesses, such as the flu, in winter.
All things considered, it is highly likely that in a given year cold causes more deaths than heat. As the planet warms, heat exposure deaths increase and cold deaths decrease. The rate of decrease in deaths from colds is faster than the rate of increase in deaths from heat. And so overall there seem to be fewer deaths from temperature exposure.
However, we should not read into this that global warming is a good thing. Climate change has long-term impacts on sea levels, animal and plant life, and agriculture, all of which can have long-lasting adverse effects on human health and well-being. Also, heat exposure deaths disproportionately affect poor regions of the world, including poor areas of the US, suggesting that temperature-related deaths have a much greater impact on them over time.