Heat acclimatization cause false indications of mortality due to ozone
Oct 12, 2005 - 4:46:38 AM
A study, published online in the journal Environmental Research, modelled the daily mortality rate of people over 65 (who suffer most of the heat-related deaths) in Greater London from 1991 to 2002. The model included daily temperatures, humidity, sunshine and wind and assessed any effects of atmospheric ozone, particulates and sulphur dioxide. UCL researchers then analysed general mortality trends for days when mean air temperatures exceeded 18oC.
The team found that when temperatures topped 18oC, mortality rates in the plus-65 group rose progressively as the days grew hotter. They also found that mortality rose more with temperature rises in early summer than in late summer when people had adjusted to heat. High levels of ozone and particulates tended to be associated with sunshine, and high particulates and sulphur dioxide with low wind, both of which can increase heat stress.
The UCL study revealed that most analyses would attribute up to half of the mortality to the pollutants, unless allowance was made for adjustment to heat in late summer, and for sunshine and wind. Most conventional studies have not allowed for these effects. The authors conclude that, contrary to earlier reports, pollutants played little part in the rise in deaths associated with hot weather in the period analysed.
Professor Bill Keatinge, of the Royal Free and University College Medical School , says: Ozone, particulates and sulphur dioxide have been fingered as the culprits when 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 air pollution. The basic message of keep cool when the weather is hot' seems to be being drowned out by exaggerated concern over air pollution. Runs of hot days are particularly dangerous.
The fact that deaths were higher in early summer rather than late summer suggests that some people were unprepared for the hot weather and may not have taken the necessary precautions to keep cool. The heat wave in France in 2003 which killed 14,000 people was an unfortunate example of what happens when people are not prepared for hot weather.
Even Britain , which has around 800 heat-related deaths in an average summer, had more than 3,000 in the exceptionally hot summer of 2003. Global warming may well produce runs of hotter days than have ever been experienced here before, and we need to be prepared for that happening in the UK with little warning.
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