Difficult to agree on climate change

I refer to Chris Knop's letter ("Official statistics on warmest years are cause for alarm", December 17) in reply to the Lai See story ("Whatever happened to global warming for the past 16 years?" December 6).

Although the Met Office in Britain responded to David Rose's article in the Mail on Sunday, there has been considerable debate both for and against. It is not entirely one way.

No matter what database is used for the analysis of temperature records, the rise in temperatures over the past 20 years has to be corrected given the influence of local urbanisation in order to reveal the "real" global warming trend. The reason for this is the bias in long temperature records for stations located in cities which are under the influence of the urban heat island effect.

This is clear in Hong Kong when only the record of the Observatory's station at its headquarters near Nathan Road is used. The same trend cannot be seen at the rural Waglan Island station, which is 15 kilometres away.

Ocean temperature measurements of 3,000 stations available since 2007 should be invaluable to resolve this in the future, as oceans hold more heat than the atmosphere. Sea level is the best indicator of long-term global warming based on earth history. However, to draw conclusions based on the short record of tide gauges in Hong Kong from 1954 without considering the many complex factors influencing local sea-level changes is misleading.

For example, the Pacific decadal oscillation may contribute up to one metre's difference in sea-level elevation between the shores of the eastern and western Pacific Ocean.

Anyone linking the occurrence of extreme weather-related events to global climate change must provide supporting evidence. In the field of climate science it is already difficult to reach a consensus when explaining regional climatic variability. Individual events have their own special circumstances.

Cleaner energy applies only to hydro, geothermal and solar. None is economically feasible for Hong Kong. The irony is that our air pollutants released into the atmosphere through the combustion of fossil fuels may reduce temperature rises caused by the local urban heat island effect.

As I pointed out in a previous letter ("Hot air about global warming ignores real culprit - water vapour", November 23), if we are serious about tackling global warming, action is needed to reduce heat generation and the predominant greenhouse effect contributor - water vapour.

Wyss Yim, Pok Fu Lam