Former Observatory directors Lee Boon-ying and Shun Chi-ming published a joint op-ed in Ming Pao on Thursday, arguing that the Labour Department relies on an inappropriate climate index that delays critical safety alerts during dangerous weather.
According to official records from the Hong Kong Observatory, the city experienced its hottest day in 143 years on Sunday, with temperatures reaching 36.9 degrees Celsius at the Tsim Sha Tsui headquarters and surging to 38.9 degrees Celsius in Sheung Shui.
Despite the historic heat, the Labour Department’s Heat Stress at Work Warning remained at amber—the baseline alert level.
Why the Current Heat Index Fails Outdoor Laborers
At the center of the controversy is the metric used to determine workplace hazards. Introduced in May 2023, the three-tier Heat Stress at Work Warning system—split into amber, red, and black levels—was designed to protect laborers from heatstroke by prompting employers to mandate longer rest breaks. However, Lee and Shun pointed out in their jointly written commentary that the system uses the Observatory’s Hong Kong Heat Index.
According to the former directors, this index is calibrated as a standard of reference for the general public, who typically spend their time inside air-conditioned environments. It is not designed to measure the severe microclimates endured by individuals performing heavy physical labor under direct sunlight. Furthermore, the two weather experts noted that the Labour Department only considers issuing an amber warning when the index hits 30, a threshold that aligns uncomfortably closely with data showing that local hospital admission rates already begin to accelerate rapidly.
The reliance on this baseline creates a dangerous operational lag. “Moreover, issuing and delivering warnings takes time, leading to a lag that prevents outdoor workers from taking timely precautions,” Lee and Shun wrote, adding that the insufficient protection ultimately fails to reassure the public. Lam Chiu-ying, another former director of the Observatory, similarly criticized the framework earlier in the week, describing the current warning setup as merely “decorative” on social media.
The Push for Wet-Bulb Globe Temperature Standards
To fix the shortcomings of the existing framework, the former Observatory chiefs are urging the government to adopt the Wet-Bulb Globe Temperature (WBGT) index. First introduced locally by the Observatory in 2008, WBGT is an internationally recognized standard that accounts for ambient temperature, humidity, wind speed, and solar radiation, providing a much more accurate reflection of physical stress on the human body.
Supporting this assessment, Lam reported via social media that monitoring data collected across the Observatory’s network showed WBGT readings exceeding 32 degrees Celsius at nine out of ten monitoring stations from last Friday through Sunday. According to Lam’s meteorological observations, these conditions should have automatically triggered a Red Heat Stress at Work Warning, while four stations recording 34 degrees Celsius last Saturday reached the black warning threshold.
“Extreme heat is the biggest ‘weather killer’ in Hong Kong, claiming more lives than severe weather events such as typhoons, rainstorms, and thunderstorms,” Lee and Shun emphasized in their op-ed. They urged officials to listen to community groups and scientific experts to adjust the policy before rising global temperatures drive even more frequent heatwaves and casualties.
Next Steps and Official Review
