Print and digital media headlines worldwide tell the story of stubbornly persistent heat domes this summer encompassing large parts of the continental U.S., Europe, and Asia. Excessive heat can be very dangerous to human health. It can lead to potentially fatal conditions such as heat exhaustion, which is exhibited by an acute loss of water and salt through profuse sweating. It can also cause heatstroke, which occurs when the body’s temperature rises so rapidly and by so much that the cooling system stops working altogether resulting in decreased sweating.
But to most vulnerable populations, the effects of heat aren’t as obvious. Heat is usually seen as a silent killer. It’s only weeks or months later when researchers examine mortality data that they observe steep rises in excess deaths following prolonged heatwaves. More than 61,000 such deaths occurred in Europe last summer.
Between 2000 and 2019, annual deaths from heat exposure increased globally. The 20-year period coincided with the earth warmed by about 0.9 degrees Fahrenheit. The heat-related fatalities disproportionately impacted Asia, Africa, and Southern parts of Europe and North America.
Some of those susceptible to heat-related deaths are people with cardiovascular disease, such as high blood pressure. Extreme heat adds strain on the heart. Others may have existing respiratory or kidney problems.
Most fatalities occur among the elderly, as they tend not to cope as well with the disequilibrium brought on by heat. In other words, it’s harder for their bodies to regulate temperature when exposed to intense heat.
Exposure to Extreme Cold Is More Fatal
According to a 2021 study published in The Lancet Planetary Health, cold is far more deadly. For every death linked to heat, nine are connected to cold.
Excessive cold can exacerbate pre-existing medical conditions such as cardiovascular and respiratory diseases. For example, death rates from myocardial infarction increase as temperatures drop. This appears to reflect the way cold can affect blood circulation. People exposed to extremely cold conditions can also suffer from direct effects such as frostbite and potentially deadly hypothermia.
Interestingly, during the 2000-2019 period examined in the study, while heat-related deaths rose, deaths from cold exposure fell. And they decreased by a larger amount than the increase in heat-related fatalities. Overall, researchers estimated that approximately 650,000 fewer people worldwide died from temperature exposure during the 2000-2019 period than in the 1980s and 1990s.
To show just how great the disparity was between cold- and heat-related deaths, looking specifically at England and Wales there were on average nearly 800 excess deaths associated with heat and 60,500 associated with cold between 2000 and 2019, according to the authors of the Lancet publication.
Curiously, U.S. data does not depict nearly such a stark contrast. Moreover, the two U.S. government agencies that track heat and cold deaths—National Oceanic and Atmospheric Administration (NOAA) and the Centers for Disease Control and Prevention (CDC)—are diametrically opposed in their estimates.
The NOAA’s account of what it calls “weather-related deaths” suggests that during the 30-year period 1988 to 2017, an average of 134 heat-related deaths occurred annually, while 30 per year were cold-related.
Contrary to the NOAA, the CDC’s National Center for Health Statistics Compressed Mortality Database, which is based on actual death certificates, indicates that roughly twice as many people die of cold in a given year than of heat.
Still, the CDC’s calculations are a far cry from the kind of numbers published in the Lancet study, both for England and Wales and the globe in its entirety.
It wouldn’t be the first time that organizations’ estimates of what are seemingly the same observable events are so far apart. Discrepancies in definitions and assumptions around measurement underlie each organization’s calculations of cold- and heat-related deaths.
Perhaps another way of approximating the relative difference in cold- versus heat-related fatalities is to compare deaths in winter and non-winter months. In the U.S., death rates in winter months have typically been 8% to 12% higher than in non-winter months. While this can be attributed to the effects of cold it’s also in part a function of the prevalence of more respiratory illnesses, such as influenza, in winter.
All things considered, it is very likely in a given year that cold causes more deaths than heat. As the planet heats up, the number of heat exposure deaths increase and fatalities due to cold decrease. The rate of decrease in deaths owing to cold is faster than the rate of increase in deaths due to heat. And so on balance there then appear to be fewer temperature exposure deaths.
However, we shouldn’t 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, each of which can have lasting deleterious effects on human health and wellbeing. Also, heat exposure deaths disproportionately impact impoverished regions of the world, including poor areas of the U.S. which implies that over time they’re much more affected by temperature-related deaths.
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