This piece is part of the Sidewalk Talk series "15 Innovations That Shaped the City."
Today's cities owe their size and success to a fundamental process of nature: steam. Before the advent of steam power, industry clung to riverbanks, where the force of moving water could be harnessed to run the machinery of factories and mills. Freed from that constraint, steam-driven industrial plants could cluster in city centers to take advantage of the larger workforces, better roads, and other services found in urban areas. Greater productivity, in turn, accelerated the process of urbanization by giving rise to higher wages, which attracted more workers, greater investments in infrastructure, and so on.
Jeremy Rifkin, author of The Zero Marginal Cost Society, explains that the importance of steam in shaping modern cities and economies is hard to overstate: "humanity made its first tentative steps into an industrial way of life that would, over the next two centuries, forever change the world."
The first safe and effective steam engine was designed to pump water out of mines in Cornwall, England. The so-called "atmospheric engine," developed by Thomas Newcomen around 1712, used steam pressure to drive a piston, which in turn drove a beam engine---essentially a large wooden beam that rocks atop a central fulcrum---to run a pump deep within a mine.
Newcomen's invention was a fuel hog, requiring an abundance of coal. It wasn't until several decades later that the Scotsman James Watt added a separate condenser, enabling the piston chamber to stay hot as steam cooled and condensed, improving energy efficiency several-fold. Watt also devised sun-and-planet gearing that turned reciprocating motion into rotary motion, allowing the steam engine to drive almost any other machinery. Watt measured the work capacity of his engines in what he dubbed horsepower; today we measure the electrical output of power plants in eponymous watts.
As steam power applications grew---primarily in transportation, energy, and manufacturing---so did their displacement of water as the primary power source of the Industrial Revolution. In 1838, steam accounted for just 5 percent of power generation in the U.S. By 1860, it was generating over 80 percent and helping drive urban and suburban expansion, with cities shedding their long-held dependence on water for their livelihoods.
Then came a secondary breakthrough from steam: the electrification of cities. Steam and electrical power may at first seem to be different types of technological advances, but as historian Maury Klein points out in his book The Power Makers: Steam, Electricity and the Men Who Made America, a direct line runs from Watt's engines to Edison's incandescent bulbs. With the advent of the coal-fired power plant in 1882, the Industrial Revolution entered a second phase. Before then, steam had been used to power reciprocating engines to run machinery. Henceforth, steam would also be used to power turbines to generate electricity.
"Without the steam engine, there would be no electricity," Klein writes, "Together they form the foundation of the modern world."
Steam made the world more urban, as factory jobs attracted the rural poor to cities. In 1801, when steam was just beginning to take over British industry, only about a third of the population of England and Wales lived in cities. By 1910, that figure reached almost 80 percent---some 36 million people. London's population grew fivefold over the same time period, and the city's air became polluted, not only from industry, but also from the growing population's use of coal for domestic heat. The city's famous fogs were really smog---fog mixed with the coal smoke issuing from a million hearths and chimneys.
"Hell is a city much like London---a populous and smoky city," wrote Percy Shelley.
With steam power came a new era of fossil fuels and what we now call the carbon economy. Before the steam engine, society ran primarily on renewable sources of energy: water, wind, biomass, and beasts of burden. After the steam engine, it ran primarily on coal, oil, and gas. The consequences of that transition are being felt worldwide as concentrations of heat-trapping greenhouse gases increase in the Earth's atmosphere, leading glaciers to melt, sea levels to rise, and heat waves to grip cities around the globe. Climate scientists warn that humanity will have to wean itself off fossil fuels almost entirely in the near future if the worst consequences are to be avoided.
Steam power may play a role in the transition to clean energy as less carbon-intensive technologies such as geothermal, nuclear, and solar-thermal continue to gain use. The world's largest solar plant---the 392-megawatt Ivanpah Solar Electric Generating Facility in the Mojave Desert---creates electricity by producing steam to spin a turbine.
Steam is also used for heat, and today some cities pipe steam underground to provide both heating and cooling (the latter by way of absorption chillers), as well as other uses such as cleaning, cooking, and sterilization. A number of cities around the world have adopted this kind of "district energy," with new design advances enabling these systems to run more easily on local renewable energy sources, dramatically reducing reliance on fossil fuels.
The benefits of district energy are even greater with the emergence of combined heat and power operations. This "cogeneration" often involves a steam turbine to produce renewable electricity; its waste energy can then heat downtown buildings and recycle water to start the steam process anew. At the largest district energy operation in the U.S., in St. Paul, combined heat and power meets 80 percent of downtown heating needs. By combining an age-old technology with a modern design, these types of systems can help cities tackle climate change at the community level.