Temperatures in densely built cities are several degrees higher than rural and suburban areas. The phenomenon, known as the city's thermal island, is due to the combination of surfaces that catch heat, low airflow, traffic and other heat-generating activities that happen in cities.
The difference tends to increase at night, as cities do not cool as much as rural areas.
Older people and children are particularly vulnerable to heat in cities, but the extreme climatic conditions affect everyone.
This is a problem that will only get worse because more people are moving to cities. According to the UN, 55% of the world's population currently lives in cities. By 2050 this figure is likely to grow to 68%.
Cities were hardest hit. Paris introduced a special heating plan designed to give its residents relief. The plan was developed after the heat wave of 2003, in which only 14,000 people were killed in France. The city builds public refrigerators in municipal buildings, fogs in the streets, and keeps parks and pools open longer than usual.
While current European temperatures of just over 100 degrees Fahrenheit may not look too high for some, they are well above seasonal averages for the region.
And since most of Europe's infrastructure and cities were built long before anyone realized the dangers of climate change, it made the heat wave even more dangerous. "Cities that are accustomed to a more temperate climate, such as London, find it very difficult to handle," Ward said. "Places experiencing cold winters tend to worry more about insulation … but of course some of the measures you design to keep warmth in winter can prevent heat from coming out in the summer, a bigger problem
This is a severe problem in the UK when one of five buildings overheats in the summer, according to the Oddi Committee of the UK United Kingdom Catherine Brown, head of the Adaptation Committee on Climate Change in the UK, told the committee that the temperature in some British hospitals may exceed 30 degrees Celsius when the outside temperature is about 22 degrees (70 in Fahrenheit)