For temperature projection, as urbanization is an additional contributor to the rising temperature of cities, the study also takes into account the urbanization effect in Hong Kong. In the lower-bound situation, the level of urbanization is frozen; in the upper-bound situation, urbanization effect grows at a constant rate. In the following, three sets of results are presented and labeled as:

(a) "middle-of-the-road" - average of the scenarios as well as of the two situations regarding urbanization;
(b) "low-end" - low emission scenario and frozen urbanization;
(c) "high-end" - high emission scenario and continued urbanization.

Compared with the 1980-1999 average of 23.1 ℃, the annual mean temperature in Hong Kong in the decade 2090-2099 is expected to rise by 4.8 ℃ according to the middle-of-the-road projection. The corresponding low-end and high-end values are 3.0 and 6.8 ℃ respectively.

As for extreme weather, the study shows that the annual number of hot nights (days with a minimum temperature of 28 ℃ or above) and very hot days (days with a maximum temperature of 33 ℃ or above) in summer will increase. On the other hand, the annual number of cold days in winter (days with a minimum temperature of 12 ℃or below) will continue to drop.

The annual number of hot nights in summer is expected to increase from the average of 15 nights in 1980-1999 to 41 nights in 2090-2099 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 30 and 54 nights respectively.

The annual number of very hot days in summer is expected to increase from the 1980-1999 average of 7 days to 15 days in 2090-2099 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 12 and 19 days respectively.

The average annual number of cold days in winter is expected to drop below one in the decade 2030-39 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 2040-2049 and 2020-2029 respectively. The average annual number of cold days at the end of the last century (1980-1999) was 14 days.

Details of the study on the temperature projections for Hong Kong in the 21st Century can be found in the paper "Temperature Projections for Hong Kong Based on IPCC Fourth Assessment Report".

Under the influence of global climate change, the average annual rainfall in Hong Kong will increase during the latter half of the 21st century. It is expected that, in the last 10 years of this century (2090-2099), the average annual rainfall recorded at the Hong Kong Observatory Headquarters will reach 2572 mm, 248 mm (11%) higher than the 1980-1999 average of 2324 mm.

Apart from the increase in the average annual rainfall in the latter half of the 21st century, the year-to-year variability in rainfall would also increase. The number of extremely wet years will increase significantly from 3 during the period 1885-2008 to 10 in the 21st century and the corresponding figure for extremely dry year is also expected to increase from 2 to 4. Here, the extremely wet and extremely dry year refer to a year with the annual rainfall at the Hong Kong Observatory Headquarters above 3187 mm and below 1282 mm respectively.

In the 21st century, the number of days with heavy rain is also likely to increase. During the last 30 years of this century, that is 2070-2099, the average number of days in a year with hourly rainfall at the Hong Kong Observatory Headquarters exceeding 30 mm would be about 6.5 days, about 1 day more than the 1980-1999 average of 5.8 days.

Further details on updated rainfall projections for Hong Kong can be found in the paper "Rainfall Projections for Hong Kong based on the IPCC Fourth Assessment Report".