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climate change

Climate Projections for Hong Kong

<<Mean sea level

Wet-bulb temperature


Against the background of global warming, it is generally expected that heat stress would increase and thermal comfort would decrease. A basic indicator of heat stress is the wet-bulb temperature. High wet-bulb temperatures indicate a warm and humid environment in which heat dissipation would be suppressed.

The Observatory utilizes data of a number of computer climate models in the IPCC Fifth Assessment Report (AR5) and statistical method to project the future change in the wet-bulb temperature in Hong Kong. Results show that regardless of the greenhouse gas concentration scenarios, the annual number of extremely warm-and-humid days (days with a maximum wet-bulb temperature of 28.2°C or above) and the annual maximum number of consecutive extremely warm-and-humid days are expected to increase in the 21st century. The increase is most significant in the high greenhouse gas concentration scenario.

concentration scenario
concentration scenario
concentration scenario
concentration scenario
high concentration scenario

Projected annual number of extremely warm-and-humid days and annual maximum number of consecutive extremely warm-and-humid days in Hong Kong under the high greenhouse gas concentration scenario

» Climate projections under different greenhouse gas concentration scenarios



Climate projection uncertainties

It is important to note that climate projection is very different from weather or seasonal forecasts. Climate projection involves assumptions in future socio-economic and technological developments and greenhouse gas emission scenarios and aims at describing the plausible change in the future climate from a long-term perspective, rather than depicting the "day-to-day" or "year-to-year" variations in weather.

Although a majority of the model projections suggests in general consistent trends for the changes in the climate of the 21st century, inter-model differences in the projections for the future climate are still rather large. This, to a certain extent, reflects that climate projection is still subject to various uncertainties in the simulation of future climate, which depend very much on such factors as future greenhouse gas emissions, the choice of models, the ability of climate models to simulate physical processes, the downscaling methodology, the stability of the statistical downscaling relationship in the future. The technique is expected to continue to improve over time as scientists know more about various physical processes that impact on the climate.