One striking feature of the nation’s energy use is the substantial increase in the quantity consumed, from about 0.3 exajoules (EJ) in 1780 to about 100 EJ in 2007. Energy use in 2000 was nearly ten times as great as it was in 1900, and in 1900 it was eighteen times as great as it was in 1800. The secular increase in energy use was driven by increases in population, economic growth, affluence, and technology. The impacts of major geopolitical and economic events are clearly visible: the Great Depression, major recessions, world wars, the oil price shocks of the 1970s and 1980s, and the COVID-19 pandemic.
Other notable features are major transitions in sources. The first century of energy use was largely about America’s prodigious forests. When the first European immigrants arrived on the North American continent around 1630, the total area of forest land was an estimated 1,037 million acres, representing about 46 percent of the total land area. Wood was harvested for space heating and the manufacture of charcoal, among other end uses.
Fodder and food were the other early sources of energy. Even as late as the first decade of the 20th century there were about 30 million horses and mules and about 100 million people in the country, and their fuel accounted for about 6% of energy use.
The first major energy source transition was the substitution of coal for fuelwood. That substitution began in earnest in the mid-19th century and was largely complete by World War I, at which time coal accounted for about three-quarters of national energy use. Much of the increase in coal use was associated with the expansion of the steam engine in stationary (factories) and mobile (railroads) end uses, and in the manufacture of steel.
The second major energy source transition was the substitution of oil (beginning 1910s) and then natural gas (beginning 1930s) for coal. This substitution was largely complete by the early 1970s. The increase in oil and gas was enabled by the advent of the internal combustion engine, advances in oil refining, and the expansion of the national gas pipeline network, among many other drivers.
The need to reduce greenhouse gas emissions to minimize the adverse effects of climate change has generated an enormous investigation of how renewable and other low-carbon sources can replace fossil fuels, the practicality of negative emissions technologies, and how fast this transition can and should happen. Regarding the United States, one thing is clear: if a rapid transition is underway, it is in a nascent stage. In 2021, fossil fuels accounted for more than 80% of primary energy use. Solar and wind are rapidly expanding in electricity generation, but the overall contribution of low-carbon energy is still small. Substantial and rapid changes in consumer attitudes and government policy at all levels are required to steer the nation toward a carbon-neutrality while simultaneously improving the well-being of all Americans.