Listen to the flowers
I remember how when I was in university there was the general concensus that when the azalea blossoms it was time for some serious study. The beautiful white, orange and magenta azeleas in full bloom in March were a timely reminder that we needed to prepare for the exams in April. However, as our weather is steadily warming, this 'alarm' system may not work anymore.
According to Leon Lau Man-chung, an arborist who conducts tree surveys in different areas of Hong Kong, plants are changing their growing cycle because of the climatic change. Some plants which usually bloom or sprout their leaves in Spring now do so as early as in December.
That's one piece of solid evidence of global warming. Another source of evidence is that six the 11 hottest years in Hong Kong history - 2001,2002, 2003, 2006, 2007 and 2009 (2009 is not quite offical yet as the Hong Kong Observatory has yet to confirm the average temperature for December) are in the past ten years, making the past decade the hottest one since the Observatory's records began in 1885.
Some people argue that there is no concrete proof that carbon emissions have led to global warming, the plants and the mercury are telling us otherwise.