European heatwaves must spur adaptation and mitigation efforts

We are, yet again, seeing unprecedented extreme heat across the Northern Hemisphere. Whether ferocious wildfires in Greece, 46c days in Sicily, records being broken in California, or 30 days in a row above 35c in Beijing, it is clear that what we are experiencing is anything but normal.

A heatwave is a period of abnormally hot weather when temperatures consistently go well beyond (often +5c, but not always) the upper limits of normal maximum ranges for a certain geographical area at a certain time of the year. Most researchers agree that 2 consecutive days of such temperatures is the minimum for a heatwave to come into existence, with five days being the criteria in other definitions.

What is considered a heatwave in one area may not be a heatwave in another. For instance, if temperatures in Oxford, UK, reached 28c for several consecutive days in July, this would be considered a heatwave, as this temperature falls well beyond the normal maximum temperature ranges for the city (which averages 18c in July and has a normal maximum of 23c). Where as a week of temperatures consistently reaching 30c in Sydney, Australia, in January would not be considered a heatwave, as the average normal temperature in this month is close to 24c and a normal maximum of 28c.

Heat waves go hand-in-hand with weather patterns called high pressure systems. Pressure in the upper atmosphere traps heat near the ground, triggering a range of feedback loops and mechanisms leading to sustained, elevated temperatures. Heat waves are more common during El Niño, a term used to describe one of two patterns of conditions (the other being La Niña) relating to ocean temperatures and wind strength that fluctuate every few years. 

It is clear that the prevalence and severity of heat waves we have seen in recent years is unusual. With a high degree of confidence, the science tells us that the frequency, intensity and timing of heat waves we are experiencing now is a direct result of human-induced climate change. The burning of fossil fuels in the past and present have interrupted and altered the nuanced feedback loops in planetary systems that maintain our climate.   

We need to not just rapidly adapt our infrastructure, cities, homes and health systems to deal with heat waves being the new norm in many regions of the world, but above all else we need to work quickly to mitigate carbon emissions.  

We are, quite literally, playing with fire, and it is time to stop.

The human health impacts are well-documented. Heat waves cause a raft of heat-related illnesses, exacerbate many symptoms in many physical and mental health conditions, worsen side effects of some medications, increase rates of hospital presentation and admission, and lead to a rise in suicide rates.  Heat waves are the leading cause of death of all extreme weather events. In Italy last week, a quarter of all hospital visits have been attributed to the effects of extreme heat (Italian society of emergency medicine, July 2023).

One of the oft-forgotten vulnerable groups during heatwaves are those with mental health conditions. Extended periods of hot weather can pose a range of challenges for those with conditions like depressive, bipolar and anxiety disorders, including acting as a trigger into certain phases of a condition, exacerbation of side effects of medications, and poor quality of sleep leading to a worsening of symptoms. Dehydration is another problem, and in some instances a lack of fluids leading to heat-related illness can have an impact on the way some medications work.

During heatwaves we see a statistically significant increase in rates of hospitalisations, overall mortality and suicide in those with underlying psychiatric disorders. The reasons are complex and seem to be an interplay between socio-economic factors, psychological state, the nature of the mental health condition itself, any underlying physical health conditions, and medications taken.

For the general population, heatwaves can also have an impact on mental health. While most of us love the sunshine and warmth, too much of a good thing can be problematic. Feeling hot and bothered, anxious, tossing and turning at night, brain fog and poor-quality decision making are all well documented impacts of being overheated.