Extreme heat here to stay even after El Niño

El Niño may have officially ended, but Hong Kong matched its record for the hottest summer solstice.[1] A 56-year-old hiker passed away in the hospital after being found unconscious with a heatstroke.[2] The brutal heat continues to claim lives around the globe. A June heat wave in Greece has killed at least six tourists;[3]and over 1,300 people died making this year’s Hajj pilgrimage in Saudi Arabia.[4] We often associate extreme heat with deserts and droughts, but it is when humidity is added into the mix that it makes heat waves exceptionally deadly.

The Acropolis, Athens’s most popular landmark, closed early amidst the heat wave (Image source: Stelios Misinas/Reuters)

You may have heard of how drinking hot drinks during summer can paradoxically cool you: this tip works by making you sweat, which then takes away the heat as it evaporates. Our ability to sweat and the physics of evaporative cooling are how our bodies can stay cool on hot days, but that depends on surrounding humidity—the more humid the air, the less evaporation can occur. This is why hot, humid days can feel especially uncomfortable; our sweat clings to our skin and soaks into our clothes, failing to cool us.

A hot drink can help cool you down—only if you are not already sweating (Image source: CUP)

When our bodies cannot cool down effectively, it can lead to heat stroke.[5] 35°C is commonly believed to be the maximum wet-bulb temperature—when the air is water-saturated, and sweat cannot evaporate—that young, healthy adults can tolerate.[6] A 2022 study suggests this threshold could be even lower, at around 31°C.[7]

Symptoms of heat stroke (Image source: Australia Wide First Aid)

What does this mean for us? Even for a city like Hong Kong that is known for its oppressive heat and humidity, taking refuge indoors with sufficient air conditioning is a simple matter for many of us. Those that have to work outdoors however—such as construction, cleaning, and delivery workers—are not as lucky. Of particular concern are the sectors which rely on an ageing workforce that is more vulnerable to the dangers of heat stress.[8] While the Labour Department has recently updated its heatstroke prevention guidance and aligned the warning system with the Hong Kong Observatory, the guidance is ultimately non-binding.[9]

A street sweeper resting and wiping off sweat (Image source: SCMP)

Even with El Niño ending, climate change will continue to expose the vulnerable population to more extreme temperatures and weather. Trying to tough out the heat is no longer a reasonable ask. As much as the government wants the industries to self-govern, heat protection policies need to be mandatory and with teeth to ensure people can work in safe and healthy workplaces. This includes the provision of water breaks, shading, resting period, and more to avoid heat stress. Moreover, the government must provide free assistance to help vulnerable and low-income households stay cool. It should also do more to educate the public on the dangers of both extreme heat and humidity and how to avoid them.

While mitigating climate change through reducing emissions is vital for stabilizing global temperatures over the long run, adapting to existing and future climate impacts is equally important for building community resilience and safeguarding public health as extreme weather intensifies in the coming decades.