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Fossil fuels—including coal, oil, and natural gas—have been powering economies for over 150 years, and currently supply about 80 percent of the world’s energy. Fossil fuels formed millions of years ago from the carbon-rich remains of animals and plants, as they decomposed and were compressed and heated underground. When fossil fuels are burned, the stored carbon and other greenhouse gases are released into the atmosphere. An excess buildup of greenhouse gases in the atmosphere has caused dramatic changes to Earth’s climate—a trend that will worsen as more fossil fuels are burned.
In 2020, oil was the largest source of U.S. energy-related carbon emissions, with natural gas close behind. The three fossil fuels contribute varying levels of emissions across sectors.
Fossil fuels are not the only way to generate electricity. Cleaner technologies such as renewable energy coupled with energy storage and improved energy efficiency can support a more sustainable energy system with zero carbon emissions.
Read more: Climate Change | Renewable Energy
Oil constitutes about one-third of U.S. energy consumption. The majority of the world’s oil is pumped out of underground reservoirs, but can also be sourced from deposits in shale and tar sands. Once extracted, crude oil is processed in refineries to create fuel oil, gasoline, liquefied petroleum gas, and non-fuel products such as pesticides, fertilizers, pharmaceuticals, and plastics. The transportation sector accounts for most oil consumption.
Globally, 100 million barrels of oil per day were produced and consumed in 2019. The United States leads the world in both oil production and consumption, producing about 18.6 million and consuming about 18.1 million barrels of oil per day in 2020.
Oil is also a major source of greenhouse gas emissions: in 2020, oil combustion was responsible for 45 percent of U.S. energy-related carbon dioxide emissions.
Extracting and transporting oil poses major environmental and safety risks. Pipelines, offshore drilling wells, and related infrastructure often leak, polluting oceans, wetlands, freshwater sources, and other ecosystems and threatening human health. Thousands of oil spills occur each year in the United States, and although many are small, they can still harm animals and humans. Major oil spills, such as the 2010 BP Deepwater Horizon disaster, which released three million barrels of oil into the Gulf of Mexico, impact ecosystems for decades.
Despite a drop in oil production and consumption in 2020 because of the COVID-19 pandemic, both are expected to return to 2019 levels within the next few years. The future of oil through 2050 remains uncertain as economies move away from fossil fuels and towards sustainable renewable energy.
Coal is primarily used to generate electricity and, in 2020, supplied 19 percent of U.S. energy consumption. Coal's share has been steadily decreasing as the costs of natural gas and renewable energy have dropped, making coal less competitive. As coal usage has dropped in the United States, so have carbon dioxide emissions from coal—by 50 percent from 2007 to 2019. In the Energy Information Administration’s 2021 Energy Outlook, national coal consumption is predicted to continue to decline between now and 2050 as coal-fired electricity plants are retired across the United States.
Coal production in the United States has been dropping since 2008 and is expected to continue to decline in the future.
Wyoming, West Virginia, Pennsylvania, Illinois, and Kentucky lead coal production in the United States. Multiple methods are employed for extracting coal, the most common of which is surface mining, which involves removing the top layers of soil and rock to access the coal. Surface mining accounts for 62 percent of coal extraction. Underground mining, which creates tunnels in mountains to access coal, accounts for the other 38 percent. Both methods create environmental and human health issues in surrounding areas.
Coal combustion produces a variety of air pollutants that harm human and environmental health, such as sulfur dioxide, nitrogen oxides, mercury, and particulate matter. Coal ash is another harmful coal waste product, which is difficult to recycle and can seep into waterways, polluting them. The Environmental Protection Agency estimates that 130 million tons of coal ash are generated each year in the United States.
Natural gas is burned to generate an increasing share of U.S. electricity and now supplies one-third of the country’s energy consumption. It is most commonly used to produce heat or electricity for buildings or industrial processes. In 2020, the United States produced about 24 percent and consumed about 22 percent of the world’s natural gas.
Accessing natural gas requires drilling a well. In the United States, natural gas is found in shale and other sedimentary rock formations and is extracted through a process called hydraulic fracturing, or fracking. Fracking requires forcing water, chemicals, and sand down a well at high pressure, which cracks the rock and releases the natural gas. This process can be extremely resource-intensive, requiring between 1.5 million gallons to 16 million gallons of water per well. Fracking can also pollute local waterways, create contaminated wastewater, and cause earthquakes.
While generating electricity from natural gas emits less carbon dioxide and other air pollutants than generating electricity from coal, leaks from natural gas plants, wells, and pipelines also emit methane—the main component of natural gas—into the atmosphere. Methane is a greenhouse gas that is 25 times more effective than carbon dioxide at trapping heat in the atmosphere, although it remains in the atmosphere for less time. Through leakage and direct emissions from combustion, natural gas was responsible for 36 percent of greenhouse gas emissions in the United States in 2020.
Natural gas consumption has been steadily increasing in the United States and is expected to continue to grow into the future as natural gas replaces coal.
Under the assumption that natural gas prices will remain low, natural gas is projected to meet an increasing share of U.S. energy demand. In particular, its use is likely to increase in the industrial sector, where it is used as a feedstock in chemical processes and for industrial heat and power.
Several options exist to transition away from a fossil fuel economy. Hydropower, biomass, wind, geothermal, and solar energy are reliable sources of renewable energy and have been a growing part of the U.S. energy mix. Nuclear energy is another zero-carbon alternative, but it is expensive and leaves behind long-lasting radioactive waste that is dangerous and costly to transport and store for disposal. Additionally, methane naturally generated by decomposition in landfills and by manure from livestock production can be captured to produce heat and power, preventing the release of methane directly into the atmosphere.
Improving the energy efficiency of buildings, vehicles, industrial processes, appliances, and equipment is the most immediate and cost-effective way to reduce energy use and cut emissions. Orienting cities and towns around public transit, walking, or biking, instead of using private vehicles, also reduces energy demand.
It is also possible for carbon emitted by the fossil fuel sector to be collected and injected back into the earth through a process called carbon capture and storage (CCS). In 2020, 26 commercial CCS plants were in operation throughout the world, capturing 40 million tons of carbon, or 0.11% of total yearly global emissions. The number of CCS plants is expected to increase as the technology continues to improve. However, increasing carbon capture and storage does not mean industries should continue burning fossil fuels unabated—fossil fuels also release other harmful pollutants. Rather, carbon capture and storage can be used to help avoid the worst effects of climate change.
See our dedicated sections for more information:
Energy Efficiency
Renewable Energy
Updated on July 22, 2021
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