Temperature projections for Hong Kong in the 21st Century

The Hong Kong Observatory announced today (August 19) the results of its recent study on projected temperature changes for Hong Kong in the 21st century.

By the last decade of this century - the 10 years between 2090 and 2099 - the annual mean temperature in Hong Kong can be expected to have risen by 3.5^oC above the 1961-1990 average of 23.0^oC. This trend is consistent with the projected warming of 1.4^oC to 5.8^oC for the entire globe. And, in the 10 years between 2090 and 2099, the annual mean minimum temperature in Hong Kong would be 3.7^oC higher than the 1961-1990 average of 20.9^oC. The annual mean maximum temperature would also be 3.7^oC higher than the 1961-1990 average of 25.7^oC.

The Assistant Director of the Hong Kong Observatory, Mr Yeung Kai-hing, said that between the late 19th century and now, annual mean temperatures recorded at the Hong Kong Observatory Headquarters had risen at a rate of 1.2^oC per 100 years. This is higher than the rising trend of 0.6^oC in the 20th century for the global mean surface temperature. He added that the annual mean temperature, annual mean minimum temperature and the annual mean maximum temperature in Hong Kong would continue to rise in the 21st century.

Mr Yeung said the present study utilised the results of supercomputer simulations of future climate made by major climate centres around the world. These centres in the United States, Canada, Britain, Germany, Australia and Japan had carried out simulations of the future climate including temperature using global climate models forced with different greenhouse gas emission scenarios. The results of these simulations have been assimilated into the assessment report of the Intergovernmental Panel on Climate Change of 2001.

The greenhouse gas emission scenarios used in the computer simulations reflect the various assumptions made by experts on the future population, economy, technology, energy and land use patterns of the world. They range from sustainable scenarios involving emission controls to rapid economic growth and fossil fuel intensive scenarios. Projections of future temperature trends in Hong Kong are made by the Hong Kong Observatory using the results of simulations made by global climate models under the various emission scenarios together with observed temperatures in Hong Kong and southern China through a technique called statistical downscaling.

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

"By the decade 2090-2099, the annual number of very hot days in summer will have risen from the 1961-1990 average of 11 days to 24 days. The annual number of hot nights in summer will see an even greater increase, from 8 nights to 30 nights. The annual number of cold days in winter will have dropped from 21 days to less than a day. There is an 80% chance that there will be no cold days in any given winter. Roughly speaking, there will not be a single cold day in eight out of every 10 years," Mr Yeung said.

Following this study on temperature projections, the Observatory will commence work on the assessment of future changes in rainfall in Hong Kong.

Assistant Director of the Hong Kong Observatory, Mr. YEUNG Kai-hing describing the Temperature Projections for Hong Kong in the 21st Century