Last year marked the warmest year ever recorded. The global average temperatures in 2023 were edging closer to 1.5C above pre-industrial levels, and for a brief period in November, they even surpassed 2C above these levels.
As the planet’s temperature increases, heatwaves become more extreme and consequently, more lethal.
Heatwaves kill more people than any other extreme weather event
Extreme heat is already the most deadly of natural hazards, causing or contributing to the deaths of more than 5,300 Australians between 1844 and 2010. And that doesn’t include the record-breaking heat of the past decade.
Heat causes selective fatalities, with the majority of casualties being individuals over 60 years old. Those aged over 85 years old have the highest risk. It also impacts those residing in socioeconomically disadvantaged regions; from 2000 to 2018, almost a third of heat-related deaths in Australia occurred in the top 20% of the most socioeconomically disadvantaged areas. Pregnant individuals, their unborn children, and young children are also more susceptible to severe heat.
It appears that Indigenous Australians have a greater ability to withstand heat compared to non-Indigenous Australians, but there are still limitations. Indigenous communities living in remote areas, specifically in desert regions, are at a higher risk of harm as temperatures reach extreme levels.
It is challenging to accurately determine the number of deaths caused by heat, as they can be misidentified as deaths from existing health conditions like heart disease and diabetes. Therefore, the current statistics are most likely lower than the actual number.
Dehydration, heart failure, and organ failure are all fatal effects of heat exposure.
As temperatures rise and become unpleasant, humans perspire. Sweating is our primary method of cooling down, as the salty liquid produced by sweat glands evaporates off our skin and releases heat. According to specialists, we can produce up to half a liter of sweat per hour.
In order to produce sweat, the body boosts blood circulation to the surface of the skin by expanding the small blood vessels found throughout the skin. However, there is a limit to how much blood flow our body has.
Dr. Aaron Bach, an environmental physiologist at Griffith University in Brisbane, explains that our heart must take into account various factors such as blood pressure, supplying muscles, the brain, and other organs. As a result, it must work harder and faster in order to effectively supply these areas.
For hearts that are already affected by aging or illness, this can result in a collapse of the cardiovascular system.
Excessive sweating causes a decrease in body fluid, which can have a negative impact on kidney function. This is due to dehydration and a decrease in blood pressure caused by increased blood flow to the skin and decreased blood flow to essential organs.
The digestive system is negatively affected by decreased blood circulation and dehydration, which can result in the release of harmful bacteria and inflammatory substances into the bloodstream, potentially resulting in organ failure.
As people age, they are more susceptible to experiencing catastrophic events. This is due, in part, to a decreased ability to sweat, which can be further compounded by pre-existing health issues like heart or kidney disease. Additionally, older individuals may have difficulty finding ways to cool down, such as relocating to a location with air conditioning.
Individuals with disabilities and young children are at a higher risk for heat-related illnesses as they may have limited ability to cool themselves down, such as being unable to access a cooling shelter.
At what point does being overheated and dehydrated lead to heatstroke?
Dehydration can occur not only from exposure to heat, but also from inadequate water intake, even in colder temperatures. However, hot temperatures and sweating increase the likelihood of dehydration. Mild dehydration may manifest in symptoms such as dizziness, nausea, dark or yellow urine, and dry mouth. Severe dehydration can result in lethargy, irritability, paleness, cold extremities, rapid breathing, and confusion.
However, during extreme heat, the main concern is heatstroke. The average body temperature ranges from 36.5C to 37.5C. Once it reaches 40.5 degrees, you are at a high risk as the body is unable to regulate the excessive heat.
This may appear as excessive sweating or a complete absence of sweating. It can also cause confusion, dizziness, nausea, disorientation, and in severe cases, loss of consciousness, seizures, and death.
“Instead of only focusing on the maximum temperature, also consider the minimum temperature.”
Heatwaves are characterized not only by abnormally high daytime temperatures over a period of three days, but also by the lack of coolness during the nighttime.
According to Professor Ollie Jay from the University of Sydney, that is the moment when your body naturally releases extra heat. If you are unable to do so, you will begin the next day at a higher temperature.
Warmer evenings result in your body, especially your heart, having to exert more effort to regulate your temperature. This leads to a decrease in the quality of your sleep, leaving you feeling fatigued at the start of the following hot day. It also causes increased dehydration, particularly if relying on fans for overnight cooling.
What is the meaning of ‘feels like’ in relation to temperature?
Describing the temperature and its effect on our perception of heat can be challenging, as it is a complex concept that goes beyond the single number provided in the nightly forecast. This number refers to the dry bulb temperature, which is the air temperature in the shade.
According to Jay, being in the sun results in exposure to temperatures 12-15 degrees Celsius higher due to absorption of radiation.
The velocity of the wind can impact your perception of heat. This is because wind, whether it is from nature or a fan, causes more evaporation from your skin, resulting in a sensation of coolness.
If the air is humid, it will be more difficult for sweat to evaporate, resulting in the temperature feeling much warmer than indicated by the numbers. This is determined by the “wet bulb” temperature, which is measured using a thermometer with a wet bulb.
It is believed that the maximum temperature for human survival is approximately 35C with 100% humidity, known as wet bulb temperature. According to Bach, one can only endure this temperature for approximately six hours before succumbing to heatstroke, regardless of their activities.
As humidity decreases, the temperature can rise to a higher level before reaching the critical threshold.
Our level of activity and clothing choices can impact our perceived level of heat. Physical movement produces heat, causing our body to work harder to regulate it. Additionally, inappropriate dressing can exacerbate the situation.
According to Jay, clothing serves as a barrier that hinders the release of heat from the body through conduction or convection. Additionally, items with a high level of resistance to evaporation can also prevent sweat from evaporating.
Tips for staying cool: place your feet in water and apply ice to the back of your neck.
The most effective techniques for staying cool focus on the individual instead of their surroundings, and also consider factors such as power usage, expenses, and environmental effects.
In hot weather, fans can provide relief by cooling the skin. However, they need electricity to operate, making them ineffective during power outages that often occur during heatwaves. Additionally, concerns about increased electricity costs may discourage people from using electric fans even when faced with extreme heat.
Fans also increase evaporation of sweat, which can increase the risk of dehydration. Misting fans and evaporative coolers can also help, but only in dry conditions and when there’s power.
According to Bach, submerging your hands and feet in tap water is a highly effective method for lowering your core body temperature. This is because our hands and feet have a large surface area, allowing for maximum heat transfer to the water.
According to Bach, using icy towels on the neck can be beneficial because the blood flow near the skin’s surface is directed towards the brain and originates directly from the heart. These towels can be either wet towels wrapped around crushed ice or soaked in a container of icy water.
According to Jay, on hot days, it is recommended to consume 250ml of water per hour based on the average amount of water lost from the body. He also cautions that relying solely on thirst as a guide may not always indicate dehydration.
On a community level, there is an increased emphasis globally on the importance of “cooling shelters” – locations like libraries, community centers, and schools that provide air conditioning, electricity, and water for individuals to seek refuge during periods of extreme heat. However, there are challenges that must be addressed in order to ensure that these shelters are available and accommodating to all members of society, including those with mobility limitations, the elderly, and individuals experiencing homelessness.
Jay explains that the solutions for various subgroups and individuals will vary. Once effective solutions are identified, the next step is to address policy and practices in both public health and individual settings.