| 英文摘要: | There has been much debate about whether winter warming due to climate change will substantially decrease mortality in that season. Research now finds that cold severity no longer predicts the number of excess winter deaths in England and Wales. For centuries, the seasons and weather have been considered fundamental determinants of human health. In temperate climates, there is a distinctive seasonal pattern of mortality — with a significant number of additional deaths in winter — known as excess winter deaths (EWDs). Assessments of the health impacts of climate change have often concluded that a reduction in the severity and length of cold weather because of global warming would substantially reduce EWDs1, 2. However, the accuracy of these predictions depends on how much of this winter mortality is directly dependent on cold outdoor temperatures, as opposed to other factors. Writing in Nature Climate Change, Staddon and colleagues3 suggest that the association of annual variation in EWDs with the number of cold days that was observed until the mid-1970s has now disappeared, leaving only the incidence of influenza-like illnesses to explain any of the yearly variation in EWDs during the past decade. By looking at data for England and Wales, they conclude it is unlikely that EWDs will decrease in the region if winters warm with climate change. It has long been recognized that in England and Wales mortality is much higher in the winter than the rest of the year4. This seasonal pattern is consistent across much of the world, and most countries suffer 10% to 30% EWDs5. A complex range of specific causes explains seasonal mortality, including the high incidence of cardio-respiratory and infectious diseases in the winter and the direct impact of cold weather. Understanding the causes of EWDs will help with disease prevention and save lives. Although much of the evidence points to the fact that cold weather is somehow responsible for EWDs, it is surprising that the level of EWDs is higher in warmer localities5. In recent years the strength of observed associations between cold temperature and winter mortality also seems to have weakened in some places6. This calls into question the assumption that outdoor temperature is the reason for the strong seasonal dependence of mortality. In fact, the complex and changing patterns of seasonal variations in mortality are likely to be related to a combination of socioeconomic, cultural and physiological adaptations to cold temperatures. Modern heating technology, along with better winter clothing, improved health care and increased prosperity and social welfare, may have reduced the harmful effects of cold weather7. The short-term effects of temperature on mortality have been widely studied in various climates, with most previous studies finding that cold temperatures increase it8. These studies usually use a time-series design to compare daily mortality counts with daily ambient temperatures. Time-series analysis has the advantage of accounting for multiple confounding factors because the same population is examined repeatedly under varying exposure conditions, such as daily temperatures, but constant (or slowly varying) covariate patterns, such as diet or smoking9. However, it is still difficult to completely separate the effects of cold temperatures, which are often measured with long lag times, from seasonality. Staddon and colleagues examine yearly data on EWDs in England and Wales through an interesting approach. The team used data over the past 60 years to identify factors associated with the decreasing trend in EWDs and its annual variation. With a detailed analysis, they show that cold outdoor temperatures now contribute little to EWDs (Fig. 1) so that milder winters resulting from climate change are unlikely to offer a public health benefit.
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![Detrended data showing the year-to-year variation in excess winter deaths compared with the number of winter days below 5 [deg]C.](http://www.nature.com/nclimate/journal/v4/n3/images_article/nclimate2146-f1.jpg)