Global warming is raising the average temperature in Korea throughout the country and all the seasons and the rate of increase is particularly high in the winter as reported by many previous studies. Nevertheless, people feel that the intensity of extreme cold in the winter is getting more severe year by year, and mass media are reporting record-breaking cold spells. Thus, this study purposed to examine whether the number of extremely cold days is actually increasing despite the rise of the average temperature and whether the number of deaths increase during the days of cold spell as suggested by these experiences.For this study, we used a total of 18 years' data on weather and death toll during the winter season. Time series analysis was applied to changes in the lowest winter temperature in 6 large cities. The 3rdpercentile data were defined cold spell.To identify the changes of the effects of cold spell yearly, we grouped the years from 92 to 2009 by 10 years and made 9 sets by excluding a previous year and then including the next year by phase. We compared effects of those 9 sets. The relationship between cold days and mortality was estimated using a quasipoisson generalized linear model. Consequently, we calculate relative risk(RR).According to the analysis result, there were increased effects of cold effects in 4 cities including Seoul and there was decrease in 2 cities.This result may be related with the adaptation according to geographical location and the status of housing or heating which is directly related with coldness because those cities were developed in different times. For the accurate interpretation, we need to consider the social and economic level and the level of urbanization of the cities. The important things is that there are increased effects of cold spell on human health year by year although winter temperature becomes higher according to global warming phenomenon. Therefore, it is needed to perform in-depth study on cold spell as well as heat wave.
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