In June the Met Office unveiled a new “extreme heat” warning system, an addition to its suite of national severe weather warnings. It didn’t have to wait long to use it. The heatwave in July led the Met Office to issue its first “amber” warning for much of England and Wales, meaning there was a risk to the health of the elderly and the very young.
Our bodies function optimally at a core temperature of around 37°C. We generate heat through metabolism and exertion; the higher the ambient temperature, the more we rely on evaporation of sweat to prevent rises in our core temperature. Babies and toddlers have immature nervous systems that are less able to perform such thermoregulation; they also depend on caregivers to ensure hydration and to adjust clothing. The ageing nervous system similarly functions less well; there is a tendency for the elderly to lose their sense of thirst and so fail to respond to dehydration. Many commonly prescribed blood pressure and heart pills affect salt and water balance, and impair the control of skin blood flow and sweat production.
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Heatwaves in 2003 and 2006 each caused more than 2,000 excess deaths in England, and comparable mortality was observed during the summer of 2020. Rates of “cot death” rise, while in the older age groups heart attacks and strokes become more common. Thermoregulation places great demands on the heart to circulate large volumes of blood to the skin, something aggravated by dehydration. Salt imbalances and water loss also affect the function of nerves and muscles, and can cause kidney failure.
Respiratory conditions such as asthma and chronic obstructive pulmonary disease frequently flare up during hot weather. There is also a connection to pollen count for those with an allergy. High concentrations of ozone are also formed at ground level during hot days, which can be toxic to the lungs and heart. Pollution-related mortality is highest in cities, where the built-up urban environment exacerbates ambient temperatures. London, for example, has recorded temperatures as much as 10°C hotter than surrounding rural areas; it can be like living in a giant storage heater.
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The Met Office’s sharpening focus on extreme weather events anticipates the effects of climate change. We have yet to see anything like the “heat domes” that killed hundreds in North America in June and July, and which are causing such problems in southern Europe. However, temperatures in the mid-30°Cs could trigger a “red” warning, meaning that even the fit and healthy are at risk. Heat exhaustion occurs as thermoregulation breaks down. Core temperature starts to rise above 38°C, and symptoms including headache, nausea, dizziness and confusion develop. Rehydration and cooling measures will rapidly reverse the condition; if not, heat stroke will supervene with potentially fatal results.
Most people can adapt physiologically during prolonged hot spells; the greatest mortality is usually seen in the first day or two as bodies struggle in temperatures that are suddenly substantially higher than usual. A heatwave is defined as lasting three days or longer, which is why the Met Office has chosen instead to emphasise “extreme heat” events in its warning system. The aim is to encourage precautions at the onset of a dramatic hike in temperature. Attention to hydration is vital. Ventilating homes overnight with cooler air, and taking measures to block the sun from windows during the day are also important, while green spaces can provide both shade and a cooler microclimate.
The health impacts of climate change are becoming starkly evident. Hopefully, they will only serve to intensify political efforts to counter climate change at Cop26 in Glasgow this November.
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This article appears in the 25 Aug 2021 issue of the New Statesman, The Retreat