Letters | Hong Kong summer highs flag the rising risks from extreme heat

Last month was Hong Kong’s hottest since records began in 1884. Not even rainstorms could do much to alleviate the heat and humidity. While most consider July to just be part of a normal summer, climate change threatens to make it a dangerous precedent.

Hot and humid weather is hard to tolerate: our bodies cannot shed heat as well since our sweat doesn’t evaporate as easily. With climate change, warmer temperatures would promote evaporation and increase humidity. Past a “wet-bulb temperature” of 35 degrees Celsius, sweat cannot evaporate at all. If sustained, this condition becomes fatal even to a fit and healthy person, and no amount of loose clothing, rest or shade would help.

Since people assume everyone can just turn on the air conditioner, heatwaves don’t draw as much attention when compared to other, more imposing, extreme weather events – but heatwaves kill more people. For example, the heatwave that swept across Europe in 2003 killed more than 70,000, despite never going above a wet-bulb temperature of 28 degrees.

We also see heatwaves becoming more frequent and intense over the years. The Hong Kong Observatory logged numerous record-breaking high temperatures throughout 2019.

A recent study by the California Institute of Technology revealed that by the mid-21st century, the heat and humidity in regions such as South Asia and the Middle East will regularly exceed our body’s limits, threatening to make those places inhospitable.