l Center for Health Statistics analyzed death certificates in the US and came to the opposite conclusion, finding roughly twice as many people die of “excessive cold” conditions than of “excessive heat” (Berko et al. 2014). About 1300 deaths per year from 2006-2010 were coded as resulting from extreme cold exposure, whereas 670 deaths per year were attributed to extreme heat.
The different findings depend, at least in part, on whether the focus is on acute or short-term responses to extreme weather or, alternatively, seasonal differences in estimates of daily mortality. Abnormally cold conditions may have little effect on estimates of daily mortality; rather deaths in winter increase as a result of non-weather-related diseases, like influenza. In addition, a recent study noted that a large majority of cold-related deaths occur under moderately cold conditions, so a reduction in extreme cold due to global warming is not expected to cause a large reduction in cold-related deaths (Gasparrini et al. 2015). It is also widely accepted that direct attribution (in medical records) of cause of death underestimates the number of people who die from temperature extremes (Sarofim et al. 2016). For example, a person who dies from a heart attack that resulted from heat or cold exposure is listed only as having died from a heart attack, even though extreme temperature exposure may have hastened or triggered the attack.
Looking to the future, the Fourth National Climate Assessment found that under an upper-bound (RCP8.5) emissions scenario we should expect a large increase in US extreme temperature deaths. In 49 large US cities, representing one-third of the nation’s population, the report projected that changes in extreme hot and extreme cold temperatures would result in 9300 additional premature deaths per year by 2090, at a cost of $140 billion per year in 2015 dollars (Ebi et al. 2018). Since the study only covered populations in large cities, Montana was not included. These mortality estimates may be reduced through adaptation efforts such as acclimatization programs (e.g., ensuring adequate heating and cooling systems, and improved insulation). The report also considered the reduction in extreme cold deaths expected in a warmer climate; approximately 100 fewer cold deaths per year were expected in the US by 2050, with no further reduction in cold deaths between 2050 and 2090 (Ebi et al. 2018)
The bottom line is that high and low temperature extremes affect vulnerable populations, such as the unwell, the poor, the young, and the elderly, among others. Understanding the extreme-temperature risk for the future requires additional in-depth study of the interaction between temperature-related deaths and socioeconomic factors. With additional information, we can avoid adverse policy outcomes and achieve effective adaptation strategies.
Human impacts from excessive heat
Heat affects humans in a variety of ways, impinging on multiple body systems. As depicted in Figure 3-2, elevated temperatures directly cause heat-related conditions ranging from muscle cramps to heat exhaustion to heat stroke, the latter of which is deadly if not treated promptly (Becker and Stewart 2011; Epstein and Yanovich 2019). In addition, elevated temperatures have been associated with increases in respiratory disease (Anderson et al. 2013; Ho et al. 2015); heart disease and strokes (Knowlton et al. 2009; Wang et al. 2016; Achebak et al. 2018); and fluid and electrolyte disorders, kidney disease, and kidney failure (Bobb et al. 2014; Ross et al. 2018; Sorensen and Garcia-Trabanino 2019). A study by Li et al. (2012) found evidence of a potential high-temperature threshold for several age groups (15–64 yr, 75–84 yr, and >85 yr) and specific heat-related causes for hospital admissions that included endocrine, genitourinary, and renal morbidities, as well as accidental injuries and intentional self-harm.
Elevated temperatures are also associated with increased risk of preterm labor (Auger et al. 2014; Ha et al. 2016; Avalos et al. 2017), as well as sudden infant death