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.

Adapting to a hotter and more humid climate isn’t as simple as staying in chilled rooms. The energy efficiency of air conditioners may have improved dramatically over the years, but they are still the biggest energy hogs. Running the air conditioner at full blast would dump more greenhouse gases into the atmosphere, as Hong Kong is still reliant on fossil fuels.

There are some technologies that may help, however. Researchers from the National University of Singapore are developing an evaporative cooling system that doesn’t cool as much but is more efficient than the conventional air conditioner. In the United States, a lab at Stanford University has developed a material to cool buildings by both reflecting heat from the sun and sending excessive heat back into space.

Still, short of overhauling our understanding of the laws of thermodynamics, these solutions only help cope with climate change and would do little to help those who need to work outdoors. We must tackle climate change now by aggressively reducing and removing greenhouse gas emissions.

Whether it is switching to low-carbon energy sources, promoting "planetary health diets”, adopting carbon capture and storage or more, we need the government to play a more proactive role in driving these large-scale changes.

They have to integrate climate objectives in policy agenda setting – going beyond environmental policies to socioeconomic policies, spatial planning and more, so as to help avoid catastrophic climate consequences.