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Thursday, 6th November 2008

Spring in autumn

Last Saturday, I went to swim without thinking that it was already November. On the way to the pool, I saw trees sprouting new leaves, magpies carrying twigs to build nests and spotted doves in feverish courtship rituals. It was every bit like spring. But it was autumn. The biological world has been fooled by the changing climate.

According to the press release (http://www.weather.gov.hk/wxinfo/news/2008/pre1101e.htm) issued by the Hong Kong Observatory (HKO), October 2008 was the hottest month of October since records began in 1884. What strikes me most is that out of the ten hottest months of October on record, five occurred in the last decade. The probability of getting it "hot" is 50% in the last decade. The overall probability over the 124-year period is 10/124, which equals about 8%. The difference of some 40% is most unlikely to be due to random chance.

Scientifically, we cannot attribute any particular hot month to "climate change" because year-to-year fluctuations do occur naturally. But with statistical data like that shown above, it leaves little doubt that October has become warmer over the decades and that the climate has indeed changed.

I take the opportunity to clarify certain press reports carrying the title of "no winter in n years". The smallest value of "n" I have seen in newspaper is "12". What the HKO has said in its last press release on the subject (http://www.weather.gov.hk/wxinfo/news/2008/pre0312e.htm) was : "The average of all calculation results based on different scenarios shows that by 2030-2039, there will be less than one cold day a year, meaning that for some winters, there will not be any cold days at all. For the situation in which the high emission scenario is coupled with continued urbanisation, the time for this to occur will be advanced to 2020 - 2029."

It refers to a situation in which the average number of cold days per year in a certain decade drops below 1. In that case, at least one of the years in that decade would have 0 cold days according to arithmetic. That would be a year "with no winter" in layman terms. There will continue to be years with winter, only that from time to time, winter would be skipped. That is what we really mean.

In the press release, HKO says that in the worst scenario, skipped winters would start appearing in the decade 2020 - 2029. One of the reporters took the earliest year 2020 and subtracted 2008 from it to get 12, thus the title "no winter in 12 years".

"No winter in 12 years" might be somewhat exaggerated. But even if it is 22 years, it would be alarming enough because it would be within the life-time of many of us. In the past, we talk about preserving the Earth for our children and grand-children. Now we could see the boomerang hitting ourselves if we do not act quickly to arrest the accelerating climate change.

I am not an alarmist. I am just an honest meteorologist reading the available data in front of me and getting concerned about the destiny of the living world, including human beings. That is why I talk about climate change all the time.

C.Y. Lam



Last revision date: <17 Jan 2013>