The study, published online in thejournal Environmental Research, modelled the daily mortality rate ofpeople over 65 (who suffer most of the heat-related deaths) in GreaterLondon from 1991 to 2002. The model included daily temperatures,humidity, sunshine and wind and assessed any effects of atmosphericozone, particulates and sulphur dioxide. UCL researchers then analysedgeneral mortality trends for days when mean air temperatures exceeded 18ºC.
Theteam found that when temperatures topped 18ºC, mortality rates in theplus-65 group rose progressively as the days grew hotter. They alsofound that mortality rose more with temperature rises in early summerthan in late summer when people had adjusted to heat. High levels ofozone and particulates tended to be associated with sunshine, and highparticulates and sulphur dioxide with low wind, both of which canincrease heat stress.
The UCL study revealed that most analyseswould attribute up to half of the mortality to the pollutants, unlessallowance was made for adjustment to heat in late summer, and forsunshine and wind. Most conventional studies have not allowed for theseeffects. The authors conclude that, contrary to earlier reports,pollutants played little part in the rise in deaths associated with hotweather in the period analysed.
Professor Bill Keatinge, of theRoyal Free and University College Medical School , says: “Ozone,particulates and sulphur dioxide have been fingered as the culpritswhen hot weather is more likely to have caused the deaths. On hot days,older people are more likely to be dying from heat stress than from airpollution. The basic message of ‘keep cool when the weather is hot'seems to be being drowned out by exaggerated concern over airpollution. Runs of hot days are particularly dangerous.
“The factthat deaths were higher in early summer rather than late summersuggests that some people were unprepared for the hot weather and maynot have taken the necessary precautions to keep cool. The heat wave inFrance in 2003 which killed 14,000 people was an unfortunate example ofwhat happens when people are not prepared for hot weather.
“EvenBritain , which has around 800 heat-related deaths in an averagesummer, had more than 3,000 in the exceptionally hot summer of 2003.Global warming may well produce runs of hotter days than have ever beenexperienced here before, and we need to be prepared for that happeningin the UK with little warning.”
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