It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. Human-induced climate change is already affecting every region across the globe and leading to a proliferation of problems, such as more frequent heat waves and extreme rainfall events, increased global proportion of major tropical cyclones, rise of sea level, reduction in agricultural production, scarcity of water resource in certain regions, spread of disease, loss of ecological and environmental balance, etc.

The observed climate change in Hong Kong is basically in line with global trends. Hong Kong has been warming up in the past hundred years or so. The numbers of hot nights and very hot days have increased significantly while the number of cold days has decreased. In addition, extreme rainfall has become more frequent, and mean sea level at Victoria Harbour is rising.