Even with swift climate change mitigation, heatwaves are projected to get worse. The number of lives lost to heatwaves depends on how sensitive our bodies are to heat, and a new study has found that we are much more sensitive to heat than you might expect.
Worldwide, over 800 deadly heatwaves have been documented since 1980, which collectively claimed the lives of tens of thousands of people. The European heatwave of 2003 killed 70,000 people alone.
Camilo Mora from the University of Hawaii at Manoa is the lead author of the study.
“We know of many case examples when people have died as a result of heatwaves,” said Mora. “However, why people died is a question whose answer is scattered.”
For the study, the research team reviewed all of the known ways that heat kills people. They identified five physiological mechanisms which impact seven vital organs. Out of 35 possible interactions between these mechanisms and organs, the researchers found medical evidence to support 27 interactions that could be a fatal result of heat.
Ischemia and heat cytotoxity are conditions that can terminally interfere with the functioning of the brain, heart, kidneys, liver, or guts. Although both conditions can be deadly by themselves, the set of physiological responses to those two attacks pose an even greater risk of death. The attack on the body from ischemia and heat cytotoxity can lead to systemic inflammatory response, for example, which is related to organ failure.
Internal complications created by ischemia, heat cytotoxity and systemic inflammatory response can cause clots that cut off the blood supply to the brain, kidneys, liver, or lungs. As a result, the depletion of clotting proteins can trigger fatal hemorrhaging even without injury.
The conditions of ischemia and heat cytotoxity can also be worsened with strenuous activity, which causes the breaking of skeletal muscle cells. This results in the leakage of myoglobin, which is toxic to the kidneys, liver, and lungs.
“Dying during a heatwave is like a terror movie with 27 bad endings to choose from,” said Mora. “It is remarkable that humanity overall is taking such a complacency on the threats that ongoing climate change is posing.”
The findings of the research suggest that all heat damaging mechanisms can be triggered any time there is substantial heat. This puts everyone at risk, with an even greater threat to those with physical ailments or who cannot afford life saving resources, like air conditioning.
The study is published in the American Heart Association journal Circulation: Cardiovascular Quality and Outcomes.