With unabating greenhouse gas emissions, the annual number of extremely warm-and-humid days (days with a maximum wet-bulb temperature of 28.2°C or above [1]) are expected to increase significantly in the 21st century.

Projected  20-year average of annual number of extremely warm-and-humid days of Hong Kong under the intermediate (SSP2-4.5), high (SSP3-7.0) and very high (SSP5-8.5) greenhouse gas emissions scenarios. (Data source: IPCC AR6)

» Projection data of extremely warm-and-humid days

Notes:

[1] Starting from the Fifth Assessment Report (AR5), the Hong Kong Observatory has adopted the following criteria to define extremely warm-and-humid days: Based on observational data from the Observatory Headquarters between 1966 and 2005, the threshold is defined as the daily maximum wet-bulb temperature reaching or exceeding the 99th percentile of that period, namely a daily maximum wet-bulb temperature of 28.2°C or above.

[2] The above climate projection results are based on the annual average number of days derived from a 20-year average and should not be directly compared with data from individual years.