There are many different kinds of manufacturing systems, all geared to the production of a bewildering variety of items, from buttons to battleships.
Each of these products starts out as raw materials. Therefore, the manufacturing sector depends on—and could be said to include—mining (for minerals), forestry (for wood), and agriculture (for the production of cotton and other natural fibers).
The U.S. mining industry uses about 366 gigawatt-hours (GWh) per year (32 million tons of oil equivalent)—mostly in the forms of diesel fuel to power excavators, trucks, and other large mobile equipment, and electricity to power conveyor belts and other smaller machines. In the case of manufacturing of plastics, fertilizers, and petrochemicals, the raw materials themselves are made from fossil fuels—primarily natural gas, natural gas liquids, and petroleum condensate.
It’s not just the extraction of the raw materials that comes with a sizable energy cost. Any raw material usually has to be transformed into a more readily usable form (iron ore into steel, bauxite into aluminum, limestone into cement), and these transformation processes often involve high heat—for example, 1,500 degrees Celsius for making cement.
Coal and natural gas are typically used for high-heat industrial processes, though electricity is employed in arc furnaces, for aluminum smelting, and in a few other applications.
Electricity accounts for less than one fifth of the final energy consumption of the U.S. manufacturing sector, according to the Energy Information Administration. The vast majority comes from oil, natural gas, coal and related by-products used both for fuel and as feedstock.
Once materials have been transformed and molded or fabricated into parts and components (often using electricity), assembly occurs using human labor or electric robots, assisted by electrically powered tools and assembly lines.
Of course, at every stage of manufacturing—from mining to final delivery of the finished product—transportation is required, which depends mostly on oil (see Transportation). Most of the products we use on a daily basis—our clothes, toothbrushes, televisions, computers, etc.—are resourced, manufactured, assembled, and packaged thousands of miles away.
Example: A Pair of Jeans
Most American families purchase their clothing items at giant discount stores. The majority of these items are made in other countries, including China, Indonesia, India, or Mexico; in fact, individual items are usually assembled in a number of different countries, depending on labor, specialization, and local resources.
Few people think much about how these clothes were made, by whom, under what conditions, or how much energy use and carbon emissions were entailed. Since their clothes are remarkably inexpensive, many American families replace them on a regular basis. The United States generates 21 billion tons post-consumer waste textiles per year, about 82 pounds per resident. Of that, 85% goes into landfills. And the amount going to landfills is growing much faster than the amount being diverted to donation or recycling.
The lifecycle of a pair of jeans can be said to fall into six phases: cotton production, fabric production, garment manufacturing, transportation & distribution (including retail), consumer use, and disposal. A small percentage of jeans will start the process again through recycling.
In 2009 and 2015, Levi Strauss published the results of lifecycle analysis of the energy and environmental impacts of a pair of 501® Jeans. They found that largest source of energy consumption and climate impact is when the jeans are washed—often in warm or hot water, which is heated directly by natural gas or fossil fuel powered electricity—and likewise dried in machines powered by fossil fuel sourced electricity.
This energy use can be easily reduced by wearing jeans more often before cleaning, by washing them in cold water, and by hang drying. And the climate impacts can likewise be reduced by using renewable energy sources for electricity.
Much more challenging is reducing fossil fuel inputs during the cotton and fabric production phases. Cotton typically comes from intensively managed farms, like those in China. High yields are achieved through seedling transplanting, plastic mulching, double cropping, plant training, and super-high plant density. However, these techniques are labor-intensive and involve a large input of chemical products like fertilizers (natural gas), pesticides (natural gas and natural gas liquids), and plastic films (natural gas and natural gas liquids).
Additionally, clothes and the raw materials that went into making them had to travel thousands of miles—usually via diesel-powered container ships. Because clothes are relatively small, lightweight items, transportation is responsible for only a minor portion of total energy expended. However, the delivery of these goods cannot easily be accomplished without oil-powered container ships and diesel-burning trucks.