The basic problem with Wrigley's interpretation is that it cannot account for per capita increase in energy consumption. The latest estimates of energy consumption by Malanima and Warde, incorporated into chapter 3, show a dramatic increase in per capita consumption of coal and wind energy in England between 1560 and 1800. Because coal was not an important source for performing mechanical work before 1830s, this per capita increase in coal consumption was essentially a per capita increase in heat consumption. The various factors whose interplay is supposed to have produced a positive feedback effect cannot possibly account for this per capita increase in heat consumption. For obvious reasons, the doubling of the population in itself cannot account for this increase; neither can urbanization. Urban areas, by their very nature, are more energy efficient, meaning greater urbanization should have slightly decreased the per capita consumption of energy. Wrigley mentions at least two factors that could explain per capita increase, but he does not directly relate them to energy consumption. The first is the western European marriage system, which, by increasing the number of nuclear households, probably increased per capita demand for space heating. The other factor probably accounts for most of the per capita increase in energy demand: the new heat-intensive industrial processes. Blast furnaces used in metallurgy, glassmaking, brewing, and dyeing all required the use of carbon-intensive and cheaply available coal to produce high temperatures required for making those consumer products.