Using weekly mortality data for London spanning 1866-1965, we analyze the changing relationship between temperature and mortality as the city developed. Our results show that both warm and cold weeks were associated with elevated mortality in the late 19th-century, but heat effects, due mainly to infant deaths from digestive diseases, largely disappeared after WWI. The resulting change in the temperature-mortality relationship meant that thousands of heat-related deaths-equal to 0.8-1.3 percent of all deaths-were averted. Our findings also indicate that a series of hot years in the 1890s substantially changed the timing of the infant mortality decline in London.

Using novel weekly mortality data for London spanning 1866-1965, we analyze the changing relationship between temperature and mortality as the city developed. Our main results show that warm weeks led to elevated mortality in the late nineteenth century, mainly due to infant deaths from digestive diseases. However, this pattern largely disappeared after WWI as infant digestive diseases became less prevalent. The resulting change in the temperature-mortality relationship meant that thousands of heat-related deaths—equal to 0.9-1.4 percent of all deaths— were averted. These findings show that improving the disease environment can dramatically alter the impact of high temperature on mortality.

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