I’m not long back from a visit to relatives in Ontario, Canada. The day after we arrived, a so-called heat dome descended on the province, bringing with it a week of very high temperatures. We experienced readings up to 33 degrees, but with a real feel when humidity was added of 41 degrees.
It was so extreme that more than 100 Canadian heat records were smashed on June 19th alone. Interestingly, the records mainly were broken in towns in Labrador, Newfoundland, New Brunswick and Nova Scotia – places not usually associated with extreme high temperature.
A national study from Statistics Canada looking at deaths related to extreme heat events found that cities where these events are less common had the greatest spike in deaths, as did cities with more renters, which are less likely to have air conditioning. We would have had a difficult time dealing with the effects of the heat dome had we not been living in an air-conditioned house.
A recent report, The Lancet Countdown: Health and Climate Change in Europe, published in Lancet Public Health, also found that global warming is costing lives, deepening health inequality and driving the proliferation of climate-sensitive diseases.
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Climate and health researcher Rachel Lowe and her colleagues used mortality and temperature data to estimate that, from 2003-2012 to 2013-2022, heat-related mortality increased by an average of 17 deaths per 100,000 people across Europe.
So how do our bodies adapt to protect us when challenged by high temperatures? Our internal temperature is controlled by a small area of the brain called the hypothalamus which functions as the body’s thermostat. When it’s hot outside, the hypothalamus triggers a series of actions that dissipate heat to ensure the body sustains its functions.
One of the first of these is a widening of the blood vessels to allow more blood to flow through them. This vasodilation is focused on blood vessels closest to the surface of the skin, which allows heat to escape.
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Sweating is another mechanism the hypothalamus controls. Sweat is secreted from special glands in the surface of the skin. This helps heat evaporate.
However, Prof Adam Taylor, writing in the Conversation, notes that the processes that help keep us cool may also put additional strain on certain parts of the body. So the heart works much harder during hot weather – beating up to 10 times more per minute for every one-degree temperature increase. Blood flow to the skin is also increased to between six to eight litres per minute, which also spikes the heart rate as it tries to cool the body, he says.
Not surprisingly, certain cardiac conditions become worse during hot spells because the cardiovascular system has to work harder than usual. All of these changes can worsen cardiac symptoms. For example, people with coronary artery disease may experience chest pain if they exert themselves during the hot weather, due to the added pressure of these cooling processes.
People with heart arrhythmias are also at increased risk of death during hot weather. A one-degree temperature increase, above 22 degrees, sees a significant increase in deaths from arrhythmias, especially in women and the over-65s.
Extreme heat also has a significant effect on kidney function. This is mainly because of sweating, which reduces fluid availability in the body and changes the electrolyte balance, causing the kidneys to work harder.
What can we do to avoid the harms of extreme heat?
- Drink plenty of fluids to replace what’s lost to dehydration. Water is better than alcohol or carbonated drinks.
- Avoid sitting in the sun. Cool off in a shady park or in an air-conditioned building.
- Take a lukewarm shower or bath.
- Place a cool flannel on the back of your neck.
- Avoid strenuous activities.
- Wear loose clothing as this allows the warm layer of air next to the body to dissipate more easily.