Tuesday, August 01, 2006

The Heat-Index.

Boy is it hot here in the US these days! It is over 100°F (37.8°C) right now in Chicago and it is so bad that the entire Chicago area is under an excessive heat warning until tomorrow. This is also the case of other cities in the country, such as New York, Boston, Washington, etc… - very much like what happened in Europe last month.

When you watch the weather on TV they always give you two indicators – the temperature given by the thermometer and the heat-index (similar to humidex in Canada). If the temperature is 100°F in Chicago right now, the heat-index which combines air temperature and relative humidity to determine how hot it actually feels, is soaring to 119°F (48.3°C).

Strangely enough, I do not think I have ever heard anything like the heat-index used in Europe or in France, despite the heat-waves that hit the continent last month. What is even stranger is that something similar is however used in France for cold temperatures in the winter (la temperature ressentie or wind-chill) which combines air temperature and wind speed. So why not use the heat-index in the summer?

It may be because the humidity in most of the US is much greater in the summer than in Europe which has typically drier summers. Also, the whole concept of both wind-chill temperature and heat-index are critized by some scientists who say that...

...creating a formula that quantifies a "feeling" illustrates the dressing-up of science for a goal which is unsuitable for it and which it will never belong to. A feeling is specific to each individual. Science studies REPRODUCTIBLE phenomena, this can not be applied, by definition, to a feeling.

On the other hand, they also agree that when the combined effects of the temperature and moisture approach the normal temperature of the body (37°C), the malaise people feel becomes dangerous for the human body. So however approximate the heat-index may be, it seems to make sense to use an indicator of some kind that warns people about the dangers their body may be exposed to - especially in this context of global warming where such extreme temperatures become more common.

It is also clear that many people would die without air-conditioning. In fact, when the power went out last night in Chicago, people (mostly seniors) had to be actually evacuated to cooling shelters.

One probably needs to find the fine line between indulgence in excessive comfort (which is sometimes the case) causing useless environmental damage and the need to keep people alive.


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