The U.S. emitted 6,586,700,000 metric tons of greenhouse gases in 2015
The United States is the world’s second largest emitter of greenhouse gases after China and produces 15% of the global annual emission of greenhouse gases. The United States has the second highest per capita greenhouse gas emissions of any nation (after Canada) with over 20.5 metric tons emitted per person per year. Over the period from 1750 to 2012 the United States alone has contributed 27% of the total cumulative amount of carbon dioxide in the atmosphere. All these greenhouse gases emitted by man are, as is well known, heating up the atmosphere and the ocean resulting in global warming and climate change.
Here we will look at the current state of the United States in terms of its greenhouse gas emissions and its energy use which is the primary source of its greenhouse gas emissions. We will consider ways in which the greenhouse gas emissions can be reduced and make simple estimates of potential reductions in different sectors of the economy. A greener, cleaner and sustainable economy for the United States is possible. This can be done by the displacement of fossil fuels for electricity generation with clean renewable energy and perhaps more nuclear power, replacing noisy polluting internal combustion engine vehicles with quiet clean electric vehicles, making buildings and electrical appliances more energy efficient and upgrading the electrical grid to a smart grid with ample energy storage capacity that can handle the variable output of renewable energy and meet the future electrical demand that will be needed by the electric vehicles.
A. GREENHOUSE GAS EMISSIONS
A.0 Overview of U.S. Greenhouse Gas Emissions in 2015.
The man-made greenhouse gas emissions from the United States in 2015 were tallied up by U.S. Environmental Protection Agency to fulfill the American commitment to the United Nations Framework Convention on Climate Change (UNFCC). They came to 6.5867 Gt CO2 equivalents (6,586,700,000 metric tons) that were reduced to a net total of 5.828 Gt of CO2 equivalents after accounting for sequestration from land use (1 Gt = 1 gigaton or 1 billion metric tons).
The bulk of the greenhouse gas emissions were carbon dioxide (5.4114 Gt) with smaller amounts of methane (0.6557 Gt), nitrous oxide (0.3348 Gt) and flourinated gases (0.1848 Gt). More than 80% of U.S. greenhouse gas emissions are due to energy use in some fashion from burning coal and natural gas to generate electricity and heat or in the use of petroleum fuels for transportation, heating or other purposes all of which emit carbon dioxide. Methane comes from gas leaks in oil and gas production, flatulence from cows and sheep and decay of organic waste in landfills and other sites. Nitrous oxide mainly comes from fertilizer use in agriculture and some forms of combustion. The fluorinated gases (also know as F-gases), which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), come from industrial processes, refrigeration and the use of a variety of consumer products.
The different atmospheric greenhouse gases absorb infrared radiation from the ground with different degrees of effectiveness and so cause different amounts of atmospheric warming for the same amount of gas. This is measured by their global warming potential relative to that of carbon dioxide. Methane has a global warming potential of 25 times that of carbon dioxide on a 100 year time span so 1 kg of atmospheric methane is equivalent to 25 kg of carbon dioxide in terms of the warming it causes. Nitrous oxide has a global warming potential of 298 on a 100 year time span. The fluorinated gases have global warming potentials that range from hundreds to thousands of times that of CO2. Amounts of non-CO2 gases are all quoted using their CO2 equivalent in this report.
The U.S. EPA defines six economic sectors for analyzing sources of greenhouse gas emissions: electricity, transportation, industry, commercial, residential and agriculture. The sources of greenhouse gas emissions in terms of these economic sector are shown below with percentages out of the total emissions of 6.587 Gt CO2 equivalents. Electricity generation and transportation accounted for 56% of the total.
A.1 Full economic sector breakdown for 2015 for all greenhouse gases
Now we will look at the emissions from each economic sector in more detail. The emissions can be divided into direct emissions that come from a variety of sources such as burning fuel to heat buildings or run vehicles, industrial processes that emit greenhouse gases in converting raw materials into finished products or emissions from farm animals. Electricity generation and distribution emits more greenhouse gases than any other sector through burning fossil fuels to generate electricity but these emissions are often reassigned to the economic sector that uses the electricity and are then considered indirect emissions by that sector. Direct emissions accounted for 70.5% of total emissions and electricity related emissions 29.5%. When direct and indirect emissions are considered, the industrial sector emitted the largest share of greenhouse gases in 2015 with 29.3% of the total.
The figures and numbers here and the next two sections are from the EPA’s “Inventory of U.S. GHG Emissions and Sinks 1990-2015“.
The primary source of greenhouse gas emissions is fossil fuel combustion that creates carbon dioxide. Other carbon dioxide emissions come from a variety of sources such as the processing of raw materials into finished products (e.g. in cement production). Methane, nitrous oxide and the flourinated gases are also emitted by each economic sector. The table below (adapted from table 2-12 in the EPA report) shows the total emissions in each category in black and also includes both CO2 and non-CO2 gases in the direct and indirect emissions from each sector. The amount of CO2 only emissions are indicated by the [ ]. Significant methane emissions are indicated by [ ], significant nitrous oxide emissions by [ ] and significant F-gas emissions by [ ]. Each sector is discussed later in more depth in the emission trends section.
|Land Use, Land Use Change, Forestry||(0.759)||(11.5%)|
Both the commercial and industrial sectors have significant amounts of non-CO2 direct emissions (43.7% and 27.7% respectively of their direct emissions). In the commercial sector these are mostly methane from landfills and some fluorinated gases and in the industrial sector these are mostly methane with smaller amounts of nitrous oxide and the flourinated gases. The direct emissions from the agricultural sector are almost entirely from nitrous oxide (fertilizer use) and methane (animal flatulence and manure management) and a small amount of carbon dioxide from the use of farm machinery. The generation and distribution of electricity produces a small amount of non-CO2 gases, mostly nitrous oxide and the flourinated gas SF6 used in circuit breakers. Transportation has a very small amount of indirect emissions from electricity used in some mass transit systems. Land use, land use changes and forests absorb CO2 and take it out of the atmosphere acting as a net sink for atmospheric CO2 in the U.S. In some other countries of the world deforestation and clearing land for settlements or agriculture acts as a net source of greenhouse gas emissions.
A.2 Greenhouse gas emissions from fossil fuel combustion in 2015
Fossil fuel combustion consumed 82% of the energy used in the U.S. in 2015, accounted for 76.7% of the total greenhouse gas emissions and 93.1% of the CO2 emissions. Greenhouse gas emissions in 2015 from fossil fuel combustion are shown below by fuel type and economic sector. Units on the left side of the graph are in million metric tons (MMT). One Gt is equal to 1,000 MMT. The emissions total to 5,050 MMT (or 5.05 Gt) of CO2. Petroleum had the largest share from fossil fuel combustion at 42.8% with natural gas and coal nearly equally split at 29% and 28.2% respectively. Coal combustion is used almost entirely for electricity generation and contributed 71% of all the carbon dioxide emissions from electricity generation. Almost all petroleum combustion is for transportation and building heating and a very small portion for electricity generation. Natural gas combustion is mostly split between electricity generation and heating of buildings. The shares from fossil fuel combustion by economic sector are: electricity generation (37.6%), transportation (34.4%), industry (15.9%), residential (6.3%), commercial (4.9%) and U.S. territories (0.81%). Some nice graphics showing the flow of carbon dioxide emissions from source to sector for the years 2014 and earlier can be found at the Lawrence Livermore National Laboratory.
Fossil fuel combustion emissions in 2015 by economic sector are shown below with emissions from electricity generation redistributed to their end-use sector (i.e. indirect fossil fuel combustion). The residential and commercial sectors used almost identical amounts of electricity and which contributed the bulk of their emissions. The indirect emissions from electricity use for each sector are: commercial 663.1 MMT (73%), residential 684.3 MMT (68.2%), industry 549.6 MMT (40.6%) and transportation 3.7 MMT (0.2%).
Transportation relies on fuels made from petroleum in the form of gasoline, diesel and jet fuel. Given the large size of the United States, the urban sprawl of its cities and the relatively small amount of public transit and railroads in use it is not surprising that transportation and hence petroleum product combustion is the single largest source of U.S. carbon dioxide emissions.
A.3 Emissions from Non-Fossil Fuel Combustion
Fossil fuel combustion emitted 5.05 Gt CO2 equivalents out of the total of 6.587 Gt CO2 equivalents emitted in 2015. The other 1.5367 Gt of emissions can be divided into these sectors: 0.499 Gt from other energy related uses (non-energy use of fuels, leaks in the natural gas and petroleum distribution networks, emissions from coal mines, waste incineration, etc.), 0.522 Gt from agriculture, 0.376 Gt from a great variety of industrial processes and product use (substitution of ozone depleting substances, iron and steel production, cement production, petrochemical production, etc.) and 0.139 Gt from waste (landfills, waste water treatment and composting). These categories are used by the Intergovernmental Panel on Climate Change (IPCC) and differ from those used by the U.S. EPA. For a detailed breakdown of greenhouse gas emissions from each of these sectors see Table 2-3 in chapter 2 of the EPA’s “Inventory of U.S. GHG Emissions and Sinks 1990-2015”.
A.4 Recent Trends in U.S. Greenhouse Gas Emissions.
Greenhouse gas emissions of the United States are show above and have stabilized in the last few decades and even decreased by 10% between 2007 and 2015 (units are in million metric tons or MMT). This is primarily a result of replacing natural gas for coal in electricity generation since natural gas burns more efficiently than coal and produces only 40% of the carbon dioxide per kilowatt-hour of electricity generated although these gains are offset somewhat by methane leakages in natural gas production and distribution. Other gains have been due to the rise of renewable energy in electrical generation, more efficient appliances that have decreased electrical demand somewhat and the renewed growth of American forests that are absorbing more carbon dioxide. Although growth in emissions has stalled major reductions in total emissions can and still need to be made.
The trend in carbon dioxide emissions from energy consumption by fossil fuel source are shown above and illustrate the recent decrease in coal use and the increase in natural gas use.
A.5 Trends in Greenhouse Gas Emissions by Economic Sector.
The trends in greenhouse gas emissions by all economic sectors over the period 1990 to 2015 are shown below. The industry, commercial and residential sectors show contributions from burning fossil fuels for heating and other uses but without their electricity usage included. The direct emissions from the agriculture, residential and commercial sectors have been very constant over the last 25 years while those from the electrical sector, transportation and industry have all peaked and then declined somewhat.
The trend in greenhouse gas emissions with electricity distributed to each end-use sector for the period 1990 to 2015 are shown below. For comparison we show the energy consumption by sector with electricity included below that (energy units are in British Thermal Units or BTU’s). Industry is the largest emitter when its electricity use is included and emitted more greenhouse gases than the residential and commercial sectors combined in the 1990’s before starting to decline after the year 2000. The residential sector has consistently used about 20% more energy than the commercial sector, mostly natural gas, and that may reflect more residential heating at night when many commercial buildings are not in use. The two sectors emitted almost the same amount of greenhouse gases with or without electricity included. The commercial sector has emissions from landfills and wastewater treatment that are comparable to the difference in emissions from energy use with respect to the residential sector. For a more detailed look at trends in carbon dioxide emissions by energy use in each economic sector see this link from the U.S. Energy Information Administration.
Carbon intensity is a measure of the amount of greenhouse gases emitted per unit of energy used. The carbon intensity in all sectors has decreased since the 1970’s but the largest decreases have been in electrical generation and the industrial sector.
Electricity. Electricity generation accounted for 37.6% of CO2 emissions from fossil fuel combustion and 29.5% (1.94 Gt) of total greenhouse gas emissions in 2015. A long term graph from the EPA of annual end-use electricity generated (in energy units of billions of kWh) shows the shares of electricity generated from each primary energy source and the total greenhouse gas emissions (dark line with scale on right). Note that neither nuclear generation nor renewable generation (hydropower, wind, solar and geothermal) produce any significant amount of greenhouse gases.
The greenhouse gas emissions from electricity generation have been declining since 2007 as natural gas generation replaces coal generation and as use of renewable energy has increased. The carbon dioxide emitted per kWh generated (the “carbon intensity”) has declined by 16% since 1990. Over the period from 1990 to 2015 the share of electricity generated by coal has dropped from 54% to 33% while the share produced from natural gas increased from 11% to 33%. During this same time period the cost of natural gas decreased by 51% while the cost of coal increased by 91%. In spite of coal producing only 33% of the electricity generated in 2015 it accounted for about 70% (1,361.9 MMT) of the greenhouse gases emitted (1,941.4 MMT) while the share from natural gas was 27.5% (534.7 MMT). The share of electricity production from the renewable sources of wind and solar went from 0.1% in 1990 to 5% in 2015. In 2016 greenhouse gas emissions from the electricity sector dropped to just below those from the transportation sector for the first time since the late 1970’s.
Transportation. Transportation accounted for 34.4% of CO2 emissions from fossil fuel combustion and 27.5% (1.81 Gt) of total greenhouse gas emissions in 2015. The sources of transportation CO2 emissions in 2015 (1.81 Gt CO2 equivalents) by vehicle type were passenger cars (42.3%), medium and heavy duty trucks (23.6%), sport utility vehicles, pickup trucks and minivans (17.1%), commercial aircraft (6.8%), rail (2.5%), other aircraft (2.3%), pipelines (2.2%), and ships and boats (1.9%). The major emissions by fuel type are gasoline (60%), distillate fuel oil or diesel (23%) and jet fuel (12%).
The long term emissions from transportation have increased somewhat due to increased amounts of travel. The total vehicle miles traveled (VMT) of all road vehicles increased by 43% between 1990 and 2015 due to population increase and hence increasing numbers of vehicles on the road, economic growth, urban sprawl and low fuel prices in the 1990’s. However, after 2007 VMT leveled off in the wake of the 2008 financial crisis but looks to be increasing again. At the same time average vehicle fuel efficiency (miles per gallon or mpg) has improved over this same time span to an average of 24.8 mpg for new vehicle models in 2015. The CO2 emission trend by fuel type (gasoline, diesel, jet fuel, etc.) can be seen here. The average road vehicle emitted 4.67 metric tons of CO2 equivalents in 2015 (see Transportation in the energy section below).
Industry. Industry accounted for 27% of CO2 emissions from fossil fuel combustion and 29.3% of total greenhouse gas emissions in 2015, the largest share of any economic sector. Direct emissions were 73.1% of the total industrial emissions (1.931 Gt) and indirect emissions from electricity use contributed 26.9%. About 54% of direct emissions from industry were from fossil fuel combustion (0.758 Gt) to produce heat or steam for industrial processes. The other 46% of direct emissions (0.654 Gt) came from processes that emit greenhouse gases such as the chemical transformation of raw materials in the production of chemicals, cement and iron and steel, the use of fuel in production or leaks in natural gas and petroleum systems. Indirect emissions from electricity use added another 0.52 Gt CO2 equivalents for running motors, electric furnaces, ovens, lighting and other uses. For a more detailed look at industrial greenhouse gas emissions see the EPA data here.
The greenhouse gas emissions from the industrial sector have been decreasing due to changes in the U.S. economy such as a decrease in manufacturing and an increase in the service sector, changes in the fuels used and by efficiency improvements. There has also been a shift from energy-intensive manufacturing products to less energy-intensive products (e.g. from steel to computer equipment). The emissions from the production of iron and steel and metallurgical coke (0.0489 Gt CO2 in 2015 or 2.5% of industrial emissions) have dropped by 51.8% since 1990 due to restructuring of the industry, technological improvements and increased scrap steel utilization.
Carbon dioxide emissions from industrial energy use by source (MMT CO2 equivalents) are shown above and are about 80-85% of total industrial greenhouse gas emissions. The decline in total industrial greenhouse gas emissions are mainly due to a declining use of coal and petroleum and decreased emissions from electricity.
Commercial and Residential. The commercial and residential sectors accounted for 11.2% of CO2 emissions from fossil fuel combustion and 33.2% (2.187 Gt) of total greenhouse gas emissions in 2015. About 37% of greenhouse gas emissions in 2015 from these sectors came from direct emissions that were mostly due to burning fuel for heating buildings and cooking. Other direct emissions come from management of waste and waste water and leaks from refrigerants in homes and businesses. The other 63% of emissions came from electrical energy use for lighting, heating, air conditioning and running appliances. Total emissions have declined somewhat from a peak in 2007 due to decreased emissions per kWh produced in the electricity sector. Electricity use in the combined sectors has increased by about 36% since 1990 but electricity related emissions only increased by 19%.
The average American home emitted 9.26 metric tons of CO2 equivalents in 2016 of which 6.672 metric tons were from electricity use (72%), 2.09 metric tons from natural gas use (22.6%), 0.23 metric tons from liquid petroleum gas (2.5%) and 0.27 metric tons from fuel oil (2.9%).
Agriculture. Agricultural activities emitted 9.3% (0.612 Gt) of the total U.S. greenhouse gas emissions in 2015. Direct emissions contributed 93% of the total and indirect emissions from electricity use 7%. Nitrous oxide emissions from fertilizer use contributed 44% of direct agricultural emissions and 75% of all nitrous oxide emissions in the U.S. Methane emissions from livestock flatulence (known as enteric fermentation) contributed 29.2% of direct emissions and methane emissions from manure management contributed 14.7%. The remaining direct emissions came from fossil fuel combustion by farm machinery (8.3%), rice cultivation (2%) and miscellaneous processes.
The trends in emissions from the agricultural sector come from changes in weather patterns, crop selection and fertilizer use that affect nitrous oxide emissions while variations in cattle population and diet affect methane emissions. The emissions from manure management have increased by 64% since 1990 from increased use of energy intensive liquid-systems.
Land Use, Land-Use Change and Forestry. Plants absorb carbon dioxide from the atmosphere to grow, sequestering it, and hence act as a sink for carbon dioxide. Increasing or decreasing the amount and type of plant life in a given area through changes in land use by clearing land, changing land from grasslands to croplands or vice versa, planting more trees and other practices make land more or less able to absorb carbon dioxide. When plants burn in forest fires or grass fires they emit carbon dioxide. Wood that is harvested from trees and then used in buildings acts as a sink for carbon dioxide whereas plants harvested for fuel act a carbon dioxide source. Overall, land use, land use changes and forests act as a net sink for U.S. carbon dioxide emissions absorbing 11.5% (0.759 Gt CO2 ) of the total greenhouse gas emissions. For a deeper understanding of how this is determined see here.
Land sequestration of carbon dioxide has decreased by 6% since 1990 due to a net decrease of carbon accumulation by forests and an increase from land converted to settlements.
The forest coverage of the U.S. has been increasing of late and is monitored by the U.S. Forest service. U.S. forests currently offset 10-15% of man-made U.S. carbon dioxide emissions per year. The graph below is from a report at the U.S. Environmental Protection agency using data collected by the U.S. Forest Service. This seems to be a somewhat different picture of the situation from that measured by the U.S. EPA. For a nice U.S. Forest Service infographic see here.
A.5 Trends in Greenhouse Gas Emissions by IPCC Sector.
The trend in U.S. greenhouse gas emission by the sectors used by the Intergovernmental Panel on Climate Change are shown below. The categories are energy, agriculture, industrial processes and product use, waste and land use, land change and forestry (LULUCF). Energy consumption is easily the largest source of greenhouse gas emissions. In the next section we look at U.S. energy production and consumption.
B.1 Total U.S. energy PRODUCTION in 2016
84 quadrillion Btu’s or 24.62 trillion kWh were produced (3412 Btu=1 kWh). Production was 86% of consumption with the difference made up by imported oil and natural gas.
|Petroleum (crude oil + natural gas plant liquids)||28.5%|
|Geothermal, Wind, Solar||4%|
|Economic Sector||(With Elec. Included)||*CO2 emissions|
*Energy consumption produced 5.174 Gt of CO2 in 2016 (petroleum 44.9%, natural gas 28.7%, coal 26.2%). Electric power percentage is out of 5.174 Gt, other sectors include emissions from electricity and so add to 100%.
In 2016 fossil fuel combustion accounted for about 81% of the total energy consumed in the U.S. while 19% came from nuclear power and renewable energy. The shares of energy consumption by energy source were: petroleum 37%, natural gas 29%, coal 15%, renewable energy 10% and nuclear power 9%.
Electricity generation used 11.1 trillion kWh of energy to make 4.08 trillion kWh of electricity, an efficiency of 36.7%. About 60-65% of the energy is lost in the electrical generating process. After accounting for electricity imports and exports and a 6% loss from transmission and distribution the final amount of electricity available came to 3.853 trillion kWh and that was divided into retail sales (3.711 trillion kWh) and direct use by the generating facility (0.142 trillion kWh). Note that every kWh of electricity saved through energy efficiency measures or other means actually saves about three times that much energy.
B.3 The distribution of energy between sources and end-use sector.
Transportation consumes 71% of all the petroleum produced and imported. Electric power generation consumes 91% of all coal produced. Natural gas is used both for electricity generation (36%) and for heating buildings, water and other uses (61%). Nuclear power is used only for electricity generation.
Another similar graphic from the Lawrence Livermore National Laboratory that includes energy lost. About 68% of energy produced is lost as waste heat or in other forms mostly in the generation and distribution of electricity and in the internal combustion engines used in transportation. For a larger version of the chart see here and for a video showing how to interpret the chart see here.
B.4 Long term energy production and consumption trends.
Long term U.S. energy production and consumption trends are shown below. For comparison we show the growth in U.S. GDP over the same time period below that.
Total energy consumption has been fairly constant since the beginning of the 21st century. The use of imported oil and natural gas has been dropping in recent years due to increased domestic production (see below). Energy exports have been increasing recently as well in the form of refined petroleum products but with a decreasing amount of coal. The U.S. economy has continued to grow in spite of the leveling of energy use. This may be due to the increasing size of the service sector and declining size of the industrial sector. The 2015 U.S. expenditures on end-use energy were $1.127 trillion or 6.2% of GDP. Adjusted for inflation this was the lowest amount spent since 2004 and was mostly due to the recent drop in the price of oil and the low price of natural gas.
Total energy production was fairly constant from 2000 to 2009 at around 71 quadrillion BTU’s but increased over the last eight years to 88 quadrillion BTU’s in 2015 before dropping to 84 quadrillion BTU’s in 2016 because of warmer winter temperatures (see also here).
Long term primary energy production, consumption and imports by all major energy sources are shown below in the next three graphs. Coal production and consumption has been declining and some coal is exported. Oil and natural gas production have been increasing but a large amount of oil is still imported as is a small amount of natural gas. Net exports of petroleum products started in 2010. The energy production of nuclear electric power and renewable energy are equal to their consumption.
a-NGPL are natural gas plant liquids and are included with oil.
Long term energy imports (crude oil, natural gas) and exports (petroleum products, coal) by source (units are in quadrillion Btu’s) are shown below.
a:Crude oil imports include imports into the strategic petroleum reserve that began in 1977. b:Petroleum products, unfinished oils, pentanes plus and gasoline blending components.
The U.S. has a large negative trade balance meaning that the total cost of goods imported to the U.S. annually exceeds the value of U.S. exports. A large portion of the negative trade balance has long been due to the need to import oil but this has changed in recent years as net oil imports have dropped. The U.S. still has a large trade imbalance but it is not due to energy imports anymore (see below, units are in billions of dollars).
B.4b Long term oil production.
Conventional oil production in the U.S. reached a peak in 1970 at 3.5 billion barrels that year and then began a long decline. A new surge in oil production began about 2008 with the exploitation of shale oil using horizontal drilling and hydraulic fracturing. There are signs that the “shale oil revolution” is already peaking and production will begin to decline in a few years.
The U.S. produced about 3.24 billion barrels of oil in 2016. The estimated proven reserves of U.S. oil are about 35 billion barrels although this estimate fluctuates depending on the price of oil and if new recoverable oil reserves are discovered. At low oil prices some reserves become unprofitable to exploit and are removed from the proven reserve estimate while conversely high oil prices mean reserves that are more expensive to exploit become available. Given these estimates, the U.S. only has 10-20 years of oil reserves left to exploit.
B.4c Long term natural gas production.
Natural gas production in the U.S., like petroleum, has seen a resurgence in the last decade due to the exploitation of shale gas using hydraulic fracturing that has added to the supplies provided by conventional gas production. The U.S. produced about 27.1 trillion cubic feet of natural gas in 2015. The estimated proven reserves of natural gas are about 324 trillion cubic feet but that estimate fluctuates with the price of natural gas. There is an additional estimated 2,136 trillion cubic feet of unproven but technically recoverable reserves. The estimated proven reserves of shale gas alone are about 200 trillion cubic feet with another 623 trillion cubic feet of unproven but technically recoverable reserves. The U.S. Energy Information Administration in January of 2015 estimated that the U.S. has an 86 year supply of natural gas at current rates of consumption although that rate is likely to increase in the future as natural gas replaces coal in electrical generation.
B.4d Long term coal production.
Coal is used almost entirely (>90%) for electricity generation. In 2015 the U.S. produced 897 million short tons of coal. The demonstrated reserve base of coal (i.e. estimated reserves) were 477 billion short tons at the end of 2015. Competition from cheap natural gas is now replacing coal as the primary fossil fuel used to generate electricity. Natural gas burns more efficiently than coal and natural gas power plants are less expensive to build than coal-fired power plants.
B.4e Long term generation of electricity
The total amount of electricity generated annually has been fairly constant over the last 15 years at about 4 trillion kWh per year. In 2016 natural gas produced 33.8% of the total electricity generated, coal 30.4%, nuclear power 19.7%, hydropower 6.5%, wind 5.6%, biomass 1.5%, solar 0.9%, petroleum 0.6% and other 0.6%. Use of coal for electricity generation has been decreasing while the share from natural gas, wind power and solar power has been increasing rapidly in the last few years. Natural gas surpassed coal as the largest single source of electric power in 2016. In the last fifteen years a net of 174 gigawatts of natural gas generating capacity has been added to the U.S. electrical grid while coal generation decreased by a net of 33 gigawatts. Total production of electricity from renewable energy, which includes hydropower and biomass in addition to wind, solar and geothermal power, exceeded nuclear power for the first time in the first quarter of 2017. Note that 4,000,000 thousand megawatthours is the same as 4 trillion kWh.
The trend in the energy consumed to produce electricity is shown above by fuel type and is compared to the amount of electricity actually generated. The rise of nuclear power in the 1970’s and 80’s is apparent as is the decline in the use of petroleum generation after the 1973 OPEC oil price hike. Coal based generation peaked in 2007. One can see that coal uses more energy to produce less electricity than natural gas, another factor in the decline of coal use. In 2016 coal used 3.07 kWh of energy to produce 1 kWh of electricity, while for natural gas the ratio was 2.18. For nuclear power the ratio was very similar to coal at 3.06. To convert quadrillion BTU’s into billion kWh’s multiply by 293 (1 qd BTU = 293 billion kWh).
The trend in the consumption of electricity in the three economic sectors that consume 96% of the total is shown above. Total electricity consumption has leveled off since the year 2000 (see here) following that of electricity production above. The increase in electricity consumption by the residential and commercial sectors has been somewhat compensated by a consumption decrease in the industrial sector.
Electricity Generating Capacity
The nameplate generating capacity of all U.S. utility scale electric generating plants in 2015 was 1,167 gigaWatts (GW) or 1.167 trillion Watts (TW) with a net summer capacity of 1,064 GW and a net winter capacity of 1,104 GW. The nameplate capacity of distributed solar power (e.g. residential and commercial building roof-tops) was estimated at 9.8 GW. There was a total of 20,068 utility scale generators in 2015. The largest plant in terms of nameplate capacity is the Grand Coulee hydroelectric dam at 7.079 GW that generates about 20.24 billion kWh annually (a capacity factor of 36%). The largest plant in terms of production was the Palo Verde Nuclear plant that generated 32.5 billion kWh in 2015 and has a nameplate capacity of 3.937 GW (a capacity factor of 93.5%).
|U.S. Utility Scale Nameplate Generating Capacity in 2015|
|Type||Capacity (GW)||Capacity Factor*||Generators|
|Hydroelectric pumped storage||21.6||N/A||156|
*Typical annual capacity factors
**Capacity factors are for combined cycle plants/steam turbine or combustion turbines
***Biomass power comes from burning wood, wood derived fuels and other forms of biomass. Capacity factors are for wood-based generation/landfill and waste generation.
Note that the maximum generating capacity (i.e. the nameplate capacity) is not fully used 24 hours a day for the entire year but depends on many factors not least of which is that equipment tends to degrade in efficiency over time. Generators are turned off or decoupled from the grid when they are not needed to meet current electrical demand, for occasional maintenance or may not run at maximum capacity in order to save fuel. Petroleum based generators are typically used only during periods of high electrical demand for example. Reactors in nuclear plants have to be refueled every 18 months or so and are turned off at that time usually for about six weeks. Hydroelectric plants may experience low water levels or water may be needed for agriculture. Wind power plants are idle if the wind is blowing too weakly or too strongly. Similarly solar photovoltaic plants only work when the sun is shining. If the 1 trillion watts of generating capacity was run continuously at full capacity it would generate the 4 trillion kWh of electricity actually made each year in 156.6 days so the entire electrical generating system has a capacity factor of about 43%.
Renewable energy capacity is growing rapidly as more solar and wind power is deployed. At the end of 2016 installed solar utility scale capacity was at 21.5 GW and wind capacity was at 81.3 GW exceeding that of hydroelectric power for the first time. Small scale distributed solar capacity had risen to 13.1 GW. The growth in biomass energy use that started in 1975 was due to increasing use of wood whereas the increase in the early 2000’s was due to the increasing use of ethanol and biodiesel as additives to gasoline and diesel. In the last few years the use of biomass for the generation of electricity has also risen.
The history of growth in generating capacity is shown below showing capacity additions and retirements since 1950. Almost all coal plants were built in the period from 1950 to 1990 while nuclear plants were built in the 1970’s and 1980’s. The phase out of petroleum plants and older coal generating plants and some nuclear plants since 2010 is apparent as is the relatively recent rise of natural gas and renewable energy generation.
The mix of generation types varies considerably from one region of the country to another. The West coast is dominated by natural gas and hydroelectric power with almost no coal fired capacity. Nuclear power is concentrated along the East coast, Great Lakes region and the South. New England and the Middle Atlantic have little coal generation with natural gas and nuclear power dominant. Coal generation is mostly in the central part of the country and the South. Natural gas is prominent in all regions except the northern great plains. Alaska and Hawaii are the only regions that use a considerable amount of fuel oil for electrical generation. For another view of the geographic distribution of electrical generating capacity see this link or go to the U.S. Energy Information Administration and use their U.S. Energy mapping system.
B.4f Long term energy consumption trends by economic sector.
The long term consumption of energy by the various economic sectors (with electricity included) is shown above. Total industrial energy use has fallen somewhat since a peak in the late 90’s while residential and commercial energy use have leveled off. Energy use in the transport sector fell somewhat since it peaked in 2007 but has risen back again almost to its peak level.
Shown above is the long term consumption of primary energy by the various economic sectors with total electrical consumption shown separately. End-use electrical energy is about one-third of primary electrical energy consumption. Transportation uses very little electricity so energy consumption is almost the same with electricity or without electricity included. Fossil fuel use (primary energy) in the residential and commercial sectors has been steady but very slowly declining since a peak in the early 1970’s. Increasing energy use in these two sectors has been entirely due to increased use of electricity. Total industrial energy consumption has been fairly constant since the early 1970’s despite substantial changes in the structure and nature of various industries. Total electrical consumption leveled off around the year 2000.
B.5 A more detailed look at energy use by each economic sector.
The United States had over 263,600,000 vehicles registered for highway use in 2015 and about 217,000 aircraft. Light-duty vehicles (passenger cars, light trucks, sport utility vehicles, vans and pick-up trucks) make up 92.1% of road vehicles with motorcycles (3.3%), heavy trucks (4.25%) and buses (0.34%) making up the rest. Petroleum products provided 92% of the energy used in transportation, biofuels (ethanol and biodiesel) provided 5% with natural gas (3%) and electricity (<1%) providing the rest.
The petroleum fuels are gasoline, diesel fuel (also known as distillate fuel), kerosene and residual fuel oil. Gasoline is used by cars, motorcycles, light trucks and boats. Diesel fuel is mostly used by heavy trucks, buses, trains, boats and ships. Kerosene is used by jet airplanes and some types of helicopters and residual fuel oil by ships. The biofuels are used as additives to gasoline and diesel fuel. Natural gas in either compressed or liquid form as well as propane are used by road vehicles, mostly in government or private fleets and to move natural gas in pipelines. Electricity is used by public transit systems and a small but growing number of electric cars. There were about 540,000 electric cars in the U.S. in 2016. The breakdown of total transportation energy use among the different types of vehicles is as follows: light trucks used 33%, cars and motorcycles 23%, other trucks 23%, aircraft 8%, boats and ships 4%, trains and buses 3%, military (all uses) 2%, pipeline fuel 2% and lubricants (<1%).
In 2016 road vehicles and boats used about 376.5 million gallons of gasoline per day or more than one gallon per person per day. Diesel fuel was consumed at a rate of 121.5 million gallons per day and jet fuel at a rate of 68 million gallons per day. For all forms of petroleum fuel the transportation sector used a total of 582 million gallons per day. The average heavy truck used 3,904 gallons of fuel in 2015 while light-duty vehicles with a long wheel base averaged 684 gallons per vehicle and light-duty vehicles with a short wheel base averaged 475 gallons per vehicle.
Each gallon of pure gasoline burned creates 19.6 pounds (8.9 kg) of carbon dioxide while gasoline mixed with ethanol creates 18.9 pounds (8.6 kg). The combustion of diesel fuel produces about 22.4 pounds (10.2 kg) of carbon dioxide per gallon. Each carbon atom of fuel burned adds two oxygen molecules to form a carbon dioxide molecule so the weight of the carbon dioxide produced is actually greater than the weight of the fuel consumed.
a-Light duty vehicle, long wheel base includes large passenger cars, vans, pickup trucks, and sport/utility vehicles with wheelbases (WB) larger than 121 inches.
b-Light duty vehicle, short wheel base includes passenger cars, light trucks, vans and sport utility vehicles with a wheelbase (WB) equal to or less than 121 inches.
In 2015, the weighted average combined fuel economy of cars and light trucks was 22.0 miles per gallon. The average vehicle traveled 11,443 miles per year in 2015. The long term graph of annual miles driven per vehicle shown below shows that American light-duty vehicles having been averaging around 10,000 miles driven per year since the 1950’s. Heavy-duty trucks began to increase their average travel distance around 1965 until leveling off near 27,000 miles per year after 1993. With these average numbers one can estimate that the average road vehicle emitted 4.67 metric tons of CO2 equivalents in 2015.
Long term energy consumption trend of the transport sector is show below. Transportation energy consumption reached a peak in 2006 before dropping a little. U.S. airline fuel use peaked in 2007 and then decreased but has started to increase again following a similar trend as in road travel. Given that average miles per vehicle seems to have leveled off the rise in energy consumption is probably due to increasing numbers of vehicles on the road and airplanes in the air as the U.S. population has increased. The share of renewable energy used for transport is currently very small but will likely grow much larger as electric vehicles become more popular. Long term transportation energy use is expected to decline as fuel economy improvements in both road vehicles and airplanes exceed increases in travel miles.
The industrial sector has the most diverse use of energy and greatest variety of greenhouse gas emissions of any sector. Industry uses about one-third of the energy produced in the U.S. and of that 66% is from direct use and 34% from electricity. The largest industrial use of energy is for petroleum refining with 31% of the total in 2010, the most recent year in which data from the U.S. EIA survey of industry is available. The other large industrial users of energy are the chemical industry with 27% of total followed by the pulp and paper industry at 11% and the metal industries at 9%. Together these four industries consume 78% of the energy used by industry.
Manufacturing processes (smelting and curing raw materials, chemical reactions, distillation, etc.) consumes about 80% of the energy used by industry. Another 15% is used to power machinery (pumps, conveyor belts, etc.) and 5% is used for powering facilities (lighting, heating, running appliances).
Long term industrial energy use by energy source. Electricity retail sales are shown below rather than the energy used to produce the electricity which is a bit more than twice that. Use of coal has been steadily declining as in other economic sectors.
The U.S. had 118.2 million housing units in 2015 with 68.4% being single family houses, 13.9% apartments and 5.8% mobile homes. With a U.S. population of 320.9 million that comes to an average of only 2.7 people per housing unit. In 2009, the most recent year from which full data from the Residential Energy Consumption Survey (RECS) conducted by the U.S. Energy Information Administration (EIA) are available, there were 113.6 million housing units that used a total of 21.077 quadrillion BTU’s with 9.788 quadrillion BTU’s lost in electrical generation and distribution. Single family homes used 80% of the energy while apartments used 15% and mobile homes 5%. The largest single use was for space heating accounting for 42% of the total. In terms of energy sources, 68.5% of the energy was in the form of electricity and 23.2% was natural gas with smaller amounts in the form of heating oil , propane and kerosene. The fossil fuels are all used for heating (both space and water) and cooking (indoor and outdoor grilling). Heating oil is used only in the Northeastern part of the United States while electricity is the dominant form of residential energy use in the South where 60% of homes primarily use electricity for space heating compared to 22% outside the South.The division of energy among various home uses:
The average housing unit used 11,306 kWh of electricity in 2009 which dropped slightly to 10,812 kWh in 2015. The average residential price of electricity in 2015 was 12.65 cents/kWh so each housing unit spent an average of $1,318 for their electricity. Alabama had the highest residential per capita consumption of electricity in 2016 with 6,619 kWh per person and Hawaii had the lowest at 1,828 kWh per person.
Total residential utility-based electricity consumption has decreased slightly in the last several years dropping by 3% between 2010 and 2016. This has been due partly to the use of residential solar photovoltaic power that has been growing rapidly in recent years with 8.57 GW of capacity installed by June 2017, an increase of 35% since June of 2016. Weather is also a factor as global warming may be lowering heating needs. Several southern states such as South Carolina, Georgia and Alabama had 25% to 30% fewer degree heating days in 2016 compared to 2010 and double digit declines in per capita residential electricity sales. More energy efficient appliances are also being used as they replace older less efficient appliances. For example, in the U.S. EIA’s 2015 RECS 18% of households reported that they had no incandescent lighting at all, instead using more efficient compact fluorescent bulbs and LED’s for lighting.
Long term residential energy sources have shown many changes over the last few decades. Coal has been phased out entirely and the once common use of petroleum has now been restricted to fuel oil used in the Northeast. Natural gas used for heating and cooking exhibited a remarkable rise in home use in the 1950’s and 1960’s but then leveled off in 1972. Electricity has largely replaced petroleum for heating and increased steadily in use until peaking in 2010. The end-use amount of electricity has leveled off at nearly the same average level as natural gas although electrical energy losses are roughly twice the end-use total. The use of air conditioning has doubled since 1980 and homes have been adding more and more appliances in the form of microwave ovens, dishwashers, clothes washers and dryers, larger TV’s, computers and other home electronics. Electric heating is now also commonplace and is the dominant form of home heating used in the South.
a-includes taxes b-excludes taxes
The real cost of residential electricity has dropped by about 59% since 1960 and that may be related to the increasing use of electricity in homes. One million Btu’s is equal to 293 kWh so $15/million Btu is equal to 5.12 cents/kWh. One million Btu’s is also equal to the energy burned by 8.3 gallons of gasoline so $10/million Btu is equal to $1.24/gallon. Inflation has caused the value of $100.00 in 1984 to rise to $235.60 in 2017 so 5.12 cents in 1984 is equal to 12.06 cents in 2017 and $1.24 in 1984 is now equal to $2.92.
The U.S. had an estimated 5.6 million commercial buildings in 2012, the most recent year surveyed by the U.S. Energy Information Administration. They occupied a floorspace of 87 billion square feet which is equal to a square with sides 55.86 miles long. Most of the buildings are small (<5,000 square feet) and comprise 50% of the total number of buildings but cover less than 10% of the total commercial building floorspace.
The largest energy source used was electricity (61%), then natural gas (31%), district heating where a central power station provides power or heat to a number of local buildings (5%) and fuel oil (3%). Natural gas is almost entirely used to heat water and interior space and to operate cooling equipment. The commercial uses of electricity are show below. Lighting is the single largest use of electricity. Note that the figure shows the total end-use electricity consumption. The energy used to generate that was actually 4,014 billion kWh.
Commercial buildings come in a variety of types depending on their use. Office buildings used more energy than any other type of commercial building. Note that the energy total in the figure below is composed of electrical end-use energy and fuel use.
Long term commercial energy sources have shown many changes over the last few decades that are very similar to the trends seen in the residential sector. Since both sectors are composed of buildings that use energy that is not unexpected. Commercial electricity use has leveled off since 2005 at an amount just a little less than the total in the residential sector. Natural gas use, following a similar trend as in the residential sector, has leveled off but at an amount only 60% of that in the residential sector. This may reflect the fact that most residential buildings are heated at night when it is cold but most commercial buildings are unoccupied and so have the heat off or turned down.
C. Some Estimates of Greenhouse Gas Emission Reductions
We have an electric future or a very hot one. We will decide by our collective actions. What will things be like in 3017? How will this era of fossil fuel use be seen in history?
The U.S. produced 6.587 Gt (or 6,587 MMT) of greenhouse gases in 2015 or a net of 5.828 Gt after accounting for land sequestration.
C.0 What would be the reduction in U.S. greenhouse gas emissions if natural gas entirely replaced coal in electricity generation?
In 2015 coal produced 1,352.4 billion kWh of electricity and created 1,350 million metric tons (MMT) of CO2 equivalents. Each kWh of electricity generated by coal created 1.002 kg of greenhouse gases.
Natural gas generation produces only 40% of the greenhouse gases emitted by coal generation per kWh. Below are carbon dioxide emissions in MMT of CO2 equivalents.
Thus if natural gas entirely replaced coal in the generation of electricity in 2015 then greenhouse gas emissions would have been reduced by 60% of the greenhouse gases emitted through coal generation or 818 MMT of CO2 equivalents. That is 12.4% of the total of 6,587 MMT of CO2 equivalents emitted by the U.S. in 2015. The share of greenhouse gas emissions by natural gas electricity production would then have doubled to 16.3% of total emissions or 1,079.5 MMT of CO2 equivalents. If the current trend in the graph above continue coal use will end sometime before 2030 but that simple trend may not continue.
C.1 The transportation sector produced 1,810 MMT of CO2 equivalents in 2015 or 27.5% of the U.S. greenhouse gas emissions. Road vehicles were responsible for 83% of the transportation emissions or 1,500 MMT of CO2 equivalents.
If all road vehicles were replaced with electric vehicles (not accounting for CO2 emissions from creation of the electric vehicles) and all electricity needed was replaced with renewables then U.S. greenhouse gas emissions in 2015 would have been lowered by 1,500 MMT or 22.8%.
Additional reductions in greenhouse gas emissions would come from a major decrease in petroleum refining that currently emits the most greenhouse gases of any industry in the industrial sector. Oil refining produced 175.1 MMT of CO2 equivalents in 2015. Other sources of greenhouse emissions come from oil fields and distribution pipelines that added 92.7 MMT of CO2 equivalents in 2016, which scaled to 2015, would be about 100 MMT for a combined total of about 275 MMT CO2 equivalents. We can estimate that the reduction in gasoline and diesel production would lower these emissions by about 75% or 206 MMT.
C.1b How much more electricity would have to be generated to supply the needs of the electric vehicle fleet? The U.S. generated about 4 trillion kWh of electricity in 2015.
Example. We can compare miles/kWh of electric cars with miles/gallon of internal combustion engine cars. A charge of 24 kWh in the battery of an electric vehicle produces 70 miles of travel, a typical measure for current electric cars. For that same 70 miles a vehicle getting 17.9 miles per gallon (the U.S. vehicle fleet average in 2015) would require 3.9 gallons of gasoline. So that is (24/3.9)=6.15 kWh/gallon. In 2016 the U.S. used 377 million gallons of gasoline per day or 137.6 billion gallons. That translates into 0.846 trillion kWh of electricity. U.S. electricity generation would have to increase from 4 trillion kWh to 4.846 trillion kWh, an increase of 21%.
We can include diesel vehicles as well. The consumption of diesel fuel was about one third that of gasoline (33.7%) so that a total of 44.3 billion gallons of diesel fuel used in 2016. Electric trucks will use more electrical energy per mile since they are heavier. If we assume the average truck is five times heavier than the average car then 120 kWh would be needed for a 70 mile trip. The mpg of trucks is lower than that of cars so we will use the average 2015 truck fuel economy of 6.4 mpg (see table 1.8 here). That comes to 10.94 gallons for a 70 mile trip so we have (120/10.94)=10.97 or 11 kWh/gallon. This increases the total amount of electricity needed for the entire future U.S. electrical vehicle fleet by 0.49 trillion kWh for a combined total of 1.34 trillion kWh. So U.S. electricity generation would have to increase by about 34% to supply the future electric vehicle fleet. This is not an unreasonable increase in the total supply of electricity that needs to be generated.
If we assume an energy loss of 66% in generating the extra electricity that comes to 4.02 trillion kWh. For comparison the amount of energy currently used in the transportation sector is about 28 quadrillion BTU’s of which 80% is used by road vehicles. That is energetically equal to 6.56 trillion kWh.or 1.63 times the energy of an equivalent electrical vehicle fleet. This implies that electric vehicles are 39% more efficient at converting primary energy into vehicle motion.So one alternative would be to use petroleum to generate the electricity needed which would cut current oil consumption by 39%. This would be the case if the current internal combustion engine road vehicle fleet was replaced with a hybrid electric vehicle fleet.
Using only coal to generate all the extra electricity needed for an electric vehicle fleet, at a rate of one kg of carbon dioxide emitted per kWh hour generated, would result in a reduction of carbon dioxide emissions by 1,500 MMt – 1,340 MMt = 160 MMt. Thus even using coal generated electricity for electric vehicles will reduce greenhouse gas emissions from the transport sector by 8.8%. If that same amount of electricity was generated entirely by natural gas then only 1,340 * 0.4 = 536 MMt of carbon dioxide would be produced for a saving of about 1,500 – 536 = 963 MMt of carbon dioxide reducing emissions from the transport sector by 53.2% or 14.6% of all 2015 U.S. greenhouse emissions.
Acknowledgements. Thanks to Morton Archibald and Affordable Energy Solutions for making this report possible.