blizzards and hurricanes get the most attention for their destructive power, but in terms of loss of life heat waves are worse, U.S. researchers say. That\'s from University of Wisconsin-Madison medical bioethicist Richard Keller, who is compiling a detailed history of the epic summer 2003 heat wave that roasted parts of Europe and killed an estimated 70,000 people. For three weeks in August that year, a massive high-pressure system stalled over Europe, bringing the hottest summer weather in more than 500 years and massive fatalities. France, in particular, was especially hard hit by the deadly period of plus-100 degree temperatures, Keller said. \"Measured by mortality, it was the worst natural disaster in contemporary France,\" he said. Social variables such as age of the victims, social status, gender and where they lived contributed to the death toll. In Paris, Keller noted, many of the victims were elderly women who lived alone, usually on the top floors of cheap, poorly ventilated walk-up apartments. \"People who lived in these apartments died like flies,\" he said. \"This was as much a social as a health and epidemiological disaster. There were social factors that made some people much more vulnerable.\" \"The single biggest factor for dying was if you lived alone.\" Those social factors will become significant as heat waves seem to be occurring more frequently and with greater intensity and duration, he said. Part of the problem, Keller says, is we build homes, apartments and public housing with more attention to staying warm in the winter than keeping cool during the dog days of summer. \"We have to recognize that heat kills far more people than the cold and that those most likely to die are people on the social margins of society,\" Keller says.