2.4 In-Depth Discussion of Sustainability Topics

Modern Energy Use

The United States accounts for 25 percent of world energy use, and its economy is a major driver of economic activity (and therefore energy use) throughout the world. In 2009, ninety-five billion MMBTU of energy was consumed in the United States. The main source of energy was from petroleum (oil), accounting for 37 percent of all energy consumed. Natural gas accounted for 25 percent, coal 21 percent, nuclear 9 percent, and renewable energy 8 percent. The United States was a net importer of energy in 2009, it imported 24 percent of the energy used, with about 85 percent of imports being petroleum based.

The four main demand sectors in the US economy are transportation, industrial, residential and commercial, and electric power generation. In 2009, the largest energy demand sector was electric power generation, consuming 41 percent of the energy supply; the next largest was transportation at 28 percent, then industrial at 20 percent, and finally residential and commercial at 11 percent.

Figure 2.8 Flow of Energy in the United States, 2009

 

US annual energy consumption peaked at 101.5 billion MMBTU in 2007, with the subsequent decline being primarily attributable to the 2008–9 recession in the United States. While currently below its peak, energy use has remained at high levels in the United States, 12 percent higher than usage in 1990.

In the early history of the United States, wood was the primary thermal energy source. In the late 1800s, coal overtook wood in terms of energy consumption. In the mid-1900s both natural gas and petroleum overtook coal in terms of overall energy consumption.

Figure 2.9

 

The current energy usage in the United States is heavily dependent on fossil fuels. Fossil fuels are fuels formed from the decomposition of dead organic material over periods of millions of years. Coal, oil, and natural gas are all forms of fossil fuels. In 2009, over 80 percent of US energy came from fossil fuels. The benefits of fossil fuels are that they are a relatively inexpensive source of energy, have historically been available in large supplies, and have a very high energy density (making them economical to use for a variety of sectors of the economy).

However, fossil fuels have drawbacks as well. They are considered nonrenewable, meaning that they can't replenish themselves - at least on a human time scale. Also in their extraction from the ground, transportation, and use, they can damage the ecosystem. These two drawbacks are the main factors that raise sustainability concerns for fossil fuels.