Urban heat island effect big factor in climate change, Hong Kong records show

Temperature and rainfall are the two most basic elements in climate change. So what can we learn from a study of local temperature records and why might it be that local factors other than carbon dioxide output are the main cause of rising temperatures in our city?

Climate change is defined by the United Nations Framework Convention on Climate Change as that attributable directly or indirectly to human activity that alters the composition of the global atmosphere and is in addition to natural climate variability. This definition challenges scientists to distinguish clearly between natural and human-induced causes.

However, the Intergovernmental Panel on Climate Change (IPCC) defines climate change as changes in the state of the climate that can be identified - for example, by using statistical tests - in such features as temperature and sea levels and that persist for an extended period, typically decades or longer. Short time periods of less than 10 years have been excluded. The changes may be due to natural variability or as a result of human activity.

The Hong Kong Observatory was established in 1883. Continuous temperature records have been kept since 1884 except during the seven years 1940-1946 encompassing the second world war.

Temperature measurements at the observatory are known historically to be influenced significantly by the urban heat island effect, defined as urban pockets that are significantly warmer than their surroundings due to human activities.

A comparative study in 1988 of temperature records from the observatory in Tsim Sha Tsui and Macau monitoring stations attributed the warmest temperatures, and a temperature increase of about 0.9 degrees Celsius at the observatory between 1884 and 1986, to heat trapping in the Victoria Harbour basin. This is best explained by the urban heat island effect resulting from rapid population growth and lifestyle changes within the basin.