Prologue Journal

How extreme heat became the deadliest silent killer among world weather disasters

• prologu5
• 09/14/202409/14/2024

Hong Kong Free Press

Unlike the visible devastation of hurricanes, floods, and tornadoes, extreme heat leaves no trace, making it deadlier than all of these extreme weather events combined.

From 2000 to 2019, about 489,000 people died from extreme heat around the world annually, according to a modelling study reported in The Lancet. Some 45 per cent of these casualties happened in Asia, the world’s most disaster-hit region from weather and climate hazards; 36 per cent were in Europe, the world’s fastest-warming continent, where heat-related mortality has increased by around 30 per cent in the past two decades.

These estimates are often much higher than official data. This is because accurate tracking of heat-related deaths is challenging and many countries still lack proper record-keeping. Unsurprisingly, heat is often referred to as a “silent killer” and it has quickly become the deadliest extreme weather event in many parts of the world.

Understanding extreme heat

To understand why extreme heat is dangerous, we must first look at how our body reacts to it.

For optimal health, the human body requires an internal temperature of around 36.5 degrees Celsius. When exposed to heat, our body initiates cooling mechanisms to keep its temperature stable, including sweating to dissipate heat through evaporation and dilating blood vessels to release heat.

In extreme heat, when the environmental temperature exceeds our body’s own temperature, these physiological processes are compromised. Elevated humidity can further complicate matters, as it hinders the evaporation of sweat from the skin and thus the body’s cooling-down process.

For people living in Hong Kong, elevated temperatures and high humidity are nothing new; temperatures frequently soar above 30 degrees and feel higher still when coupled with humidity. And yet, heat-related illnesses in the city are on the rise. A yet-to-be-published study by researchers at the University of Hong Kong found that heatwaves in the city over the past decade, 18 in total, may have contributed to 1,677 excess deaths.

As of 2022, Hong Kong had already warmed 1.7 degrees Celsius compared to pre-industrial times, according to Berkley Earth. The city just witnessed an “exceptionally hot” July, with its Observatory forecasting that 2024 will be one of the hottest years on record. The same is happening around the world.

The increase in extreme heat is a direct result of our warming planet, which is driven by greenhouse gases that trap heat in the atmosphere. This raises Earth’s surface temperature and leads to longer and hotter heatwaves.

Prolonged exposure to high temperatures without enough rest or cooling breaks can result in the accumulation of heat within the body, overwhelming its cooling mechanisms and leading to severe, sometimes deadly heat-related illnesses.

Some of the most common are heat exhaustion – with symptoms including heavy sweating, weakness, and dizziness – and heatstroke – marked by a high body temperature, confusion, and loss of consciousness. This can be life-threatening if not promptly treated.

People living in urban areas, which often lack cool environments or natural shading, are particularly vulnerable. But in a rapidly warming world, another issue is emerging: nighttime heat.

High temperatures at night prevent the body from recovering from daytime heat. This not only disrupts sleep, which can negatively affect physical and mental health, cognitive function, and life expectancy, but also increases the risk of illness and mortality.

A 2020 study by the Chinese University of Hong Kong found that five consecutive “hot nights,” defined as when temperatures rise above 28 degrees Celsius, would raise the risk of death by 6.66 per cent.

People without access to air conditioning – a huge proportion of the world’s population – are particularly at risk. While about 90 per cent of households in the US and 60 per cent in China have some sort of air conditioning system, the number is lower in rapidly warming places like Europe, where 10 per cent have access to air conditioning, and India, where that number is 8 per cent. In sub-Saharan Africa and South Asia, the percentage is even lower.

With climate change, nights are not just getting warmer, they are doing so faster than days in many parts of the world. According to a Climate Central analysis published earlier this month, 2.4 billion people experienced an average of at least two additional weeks per year where night-time temperatures exceeded 25 degrees between 2014 and 2023.

More than 1 billion people experienced an average of at least two additional weeks per year of nights above 20 degrees and 18 degrees Celsius.

Tracking casualties is complicated

So far this year, Thailand reported 61 heat-related casualties and India 143. Meanwhile, at least 30 heat-related fatalities were confirmed across the western US in July alone. A month earlier, 1,301 Hajj pilgrims were killed in scorching heat in Saudi Arabia. These numbers, however, are just a fraction of the true toll.

Unlike more immediate threats, such as severe storms or earthquakes, heat-related conditions can gradually build up. They also affect vulnerable populations disproportionately, and may not be seen as imminent dangers until symptoms like heat exhaustion or heatstroke manifest suddenly and severely, leading to heat-related illnesses and fatalities without obvious warning signs.

To further complicate matters, heat-related illnesses and deaths can be multifactoral, involving a combination of heat exposure, individual susceptibility, and underlying health conditions.

For those with pre-existing conditions such as diabetes, kidney disease, respiratory or cardiovascular conditions, heat-related stress can trigger or worsen symptoms, leading to serious health complications and, in severe cases, death. In these cases, determining the exact contribution of heat to a death can be complex, as it less likely that fatalities in which temperatures played an indirect role are classified as heat-related deaths.

Who is at risk?

While no one is truly immune to extreme heat, there are factors that can increase an individual’s vulnerability.

Susceptibility to heat, and how effectively the human body regulates its temperature in extreme conditions, is influenced by a combination of aspects such as age and health, as well as exposure variables including occupation and socio-economic circumstances.

Generally speaking, studies show that women and particularly pregnant women, children, and the elderly are especially at risk.

In an August statement, UNICEF said one in five of the world’s children – or 466 million – would experience double the number of extremely hot days compared to their grandparents. It said rising temperatures across Europe and Central Asia killed an estimated 377 children in July 2021.

UNICEF Executive Director Catherine Russel explained that children’s bodies are “far more vulnerable” to extreme heat. “Young bodies heat up faster, and cool down more slowly. Extreme heat is especially risky for babies due to their faster heart rate, so rising temperatures are even more alarming for children,” she said.

UNICEF said extreme heat has been linked to pregnancy complications, including “gestational chronic diseases and adverse birth outcomes including stillbirth, low birth weight, and preterm birth.”

Heat stress on pregnant women can also lead to child malnutrition and leave infants more vulnerable to infectious diseases such as malaria and dengue, which spread in high temperatures.

The number of people exposed to extreme heat is growing exponentially due to climate change. Between 2000 to2004 and 2017 to 2021, heat-related deaths among individuals aged 65 and older surged by around 85 per cent. Age-related physiological changes, such as a decrease in the body’s ability to regulate its temperature and reduced sweating capacity, make older adults less efficient at dissipating heat.

Pre-existing health conditions and medications can further compromise their ability to cope with high temperatures. Social isolation, limited mobility, and inadequate access to cooling resources only exacerbate these vulnerabilities.

Other factors heightening heat vulnerability have to do with race and ethnicity. Pre-existing health conditions that are more prevalent in certain ethnic or racial groups can increase susceptibility to heat-related illnesses. Examples include diabetes or cardiovascular diseases. But socio-economic circumstances also play a role.

Ethnic and racial minorities often face higher rates of poverty and may live in urban areas with fewer green spaces and more concrete surfaces. Temperatures in these neighbourhoods are generally significantly higher.

In the US, an Environmental Protection Agency review of multiple studies revealed that low-income neighbourhoods and those with larger populations of people of colour often experience higher temperatures compared to wealthier mainly white neighbourhoods in the same city.

Another striking example where this is an issue is Hong Kong. The city’s infamous subdivided flats and “cage homes” are becoming increasingly greater health risks as the city faces higher temperatures in the warm seasons.

Anti-poverty local NGO the Society for Community Organisation in July warned of extreme temperatures in subdivided flats, which house more than 220,000 people. The NGO surveyed 308 people living in “inadequate housing,” who often do not have access to or cannot afford ventilation or air conditioning. Over 90 per cent of them said they “felt ill because their apartments were too hot.”

“The heat makes it very hard for me… I feel tired,” 84-year-old Chun Loi, who lives in a windowless, poorly ventilated, one-room flat in Hong Kong, told AFP on a hot summer day. “I try to stay in as much as possible with my fans… Otherwise, where can you go? It’s embarrassing to stay in restaurants and malls if I am not eating anything,” Chun said.

As Eva Yeung of Red Cross Hong Kong put it: “Climate change affects everyone. But the impact is not equal because some people, due to their living conditions and physical conditions, are affected more than others.”

Outdoor workers are also highly vulnerable. The International Labor Organization estimates that almost 4 per cent of the world’s total working hours could be lost to climate-induced extreme temperatures by 2030.

A 2022 Oxfam Hong Kong study on working conditions in waste collection centres in the city revealed that inside temperatures averaged 32.2 degrees Celsius, surpassing the July average by two degrees. Issues such as poor ventilation, heat, humidity, pests, foul odours, and a lack of rest areas are prevalent in both existing and renovated waste collection centres.

Under these circumstances, over 60 per cent of cleaners expressed experiencing discomfort while on duty. More than 70 per cent indicated that they must stay in cooler and shaded areas along the streets for breaks and meals. Upon returning home, they may still have to endure extreme hot weather. 

Street cleaners face a similar threat. According to interviews by Hong Kong-based group Concern for Grassroots’ Livelihood Alliance in August, 90 percent of the street cleaners reported fatigue, thirst, headaches, dizziness, increases in body temperature, and nausea while working, even though their employers provided portable fans.

“I have to drink seven bottles of drinks a day, including water, homemade herbal tea, energy drinks, and more,” Pattie, a 55-year-old cleaner, told HKFP in July. “Sometimes, when it’s too hot, even the taste of water makes me feel nauseous.”

Irreversible trend?

An October 2023 study warned that heat and humidity levels will reach lethal levels for hours, days, and even weeks in some parts of the world by the end of the century, even below 2 degrees Celsius of warming, making it impossible to stay outdoors. 

Since the 1970s, climate scientists have warned that the relentless burning of fossil fuels is heating up our planet, and that crossing a specific warming threshold could lead to irreversible impacts.

See also: Wealthy Hong Kong districts will warm at a cooler pace than poorer areas, study finds

But the world has been slow to react to these warnings and what we are experiencing now is the result of this inaction.

The past nine years have been the hottest on record, and 2023 was the hottest year globally, with global average temperatures at 1.46 degrees Celsius above pre-industrial levels. Scientists are almost certain that 2024 will be even warmer.

According to the Intergovernmental Panel on Climate Change, with further global warming, we can expect an increase in the intensity, frequency and duration of heatwaves. And unless we prepare societies to deal with this, extreme heat will continue to claim millions of lives.

This story originally appeared on Earth.org.

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