Climate Change Impact on Hong Kong - a Scientific Perspective
We are stepping into a new era of climate records. As the global atmospheric concentration of carbon dioxide continues to climb at a rate of 2 to 3 ppm per year, reaching 404.7 ppm in December 2016, we are seeing more warming-related record-breaking events in the past couple of years, including a 16-month long sequence of monthly global temperature records from May 2015 to August 2016. The record of yearly global temperature has now been broken for three consecutive years, with the temperature in 2016 standing at 1.1oC above pre-industrial levels. The Arctic is warming at more than twice the rate of the rest of the world, and the monthly Arctic sea ice extent record has been broken nine times in the past 14 months. Recently, the sea ice around Antarctica also shrank to its lowest summertime area on record.
Hong Kong is not immune to the impacts of climate change. Even allowing for the urbanization factor, we have experienced a significant warming trend in the past 130 years or so, and the annual number of very hot days has increased six-fold in the past century. With more frequent extreme weather expected as a result of climate change, the chance of hourly rainfall exceeding 100 mm has since doubled. In line with the rising global mean sea level, an average sea level rise of around 3 mm per year is recorded at the Victoria Harbour.
According to the projection results of studies undertaken by the Hong Kong Observatory, the annual mean temperature of Hong Kong in the last decade of this century is expected to be about 1.5 – 3.5oC above the average temperature of 1986-2005, even if emission reductions pledged under the Paris Agreement materialize. If the pledges are not met and we carry on regardless towards the IPCC AR5 “worst case scenario”, the annual number of very hot days in Hong Kong will exceed 100, and the duration of high heat stress as well as the severity of heat stress will correspondingly increase. Average rainfall intensity will be enhanced as well, and the annual maximum 3-day rainfall could reach 500 mm towards the end of this century. By then, the mean sea level rise in Hong Kong and its adjacent waters is expected to be about 1 m above the level in 1986-2005, and a 1-in-50 years extreme sea level event under the current climate, such as storm surge triggered by the passages of typhoons, may become an annual occurrence.
The Hong Kong Observatory looks forward to working closely with government departments, stakeholders and the community to make Hong Kong a climate resilient city for this generation and beyond.