Energy-related carbon dioxide emissions vary significantly across states. An analysis of state-level emissions data from 2000 through 2010 released by the U.S. Energy Information Administration (EIA) shows that the overall size of a state, as well as the available fuels, types of businesses, climate and population density, play a role in both total and per capita emissions. For example, some states are located near abundant hydroelectric supplies, while others contain abundant coal resources.
Over the time period from 2000 to 2010, carbon emissions fell in 32 states and rose in 18 states. The greatest percentage decrease in carbon dioxide emissions occurred in Delaware at 28 percent, (4.5 million metric tons). The greatest absolute decline was 58.8 million metric tons in Texas (8.3 percent). New York experienced a decline of 38.6 million metric tons (18.3 percent). The greatest percentage increase was in Nebraska at 16 percent (6.6 million metric tons), while Colorado experienced the greatest absolute increase (11.8 million metric tons or 13.9 percent).
From 2009 to 2010, only 14 states saw a decrease in emissions. The U.S. was rebounding from the recession and emissions from consumption of energy was up in most states. Because of differences in data aggregations it is difficult to compare the total for all states with the total for the U.S.
Emissions by fuel
States exhibit very different emissions profiles by fuel type. For example, in 2010, coal consumption accounted for 80.8 percent of carbon dioxide emissions in West Virginia. In California, 65.2 percent of carbon dioxide emissions came from petroleum, while only 1.4 percent came from coal. Rhode Island had no emissions from coal consumption, but 46.1 percent of its emissions were from natural gas.
Vermont’s share of carbon dioxide emissions from petroleum was 92.5 percent and Hawaii’s share was 91.4 percent in 2010. No other states exceeded 80 percent in terms of the share of emissions from petroleum; Maine’s petroleum share was 75.6 percent.
Emissions by sector
There can also be significant variations in terms of carbon dioxide emissions by sector —even for states that have similar fuel emissions’ profiles. These variations are due to factors such as the use of different fuels for electricity generation, climate, and sources of economic outputs (e.g., commercial versus industrial activity).
For example, in Vermont the largest share of emissions in 2010 came from the transportation sector (58.7 percent), predominantly from petroleum, but the electric power sector share is small (0.1 percent) because of Vermont’s reliance on nuclear power. Vermont’s residential sector share was 22.1 percent — indicative of a relatively cold climate where petroleum is the main heating fuel.
Hawaii, where a dominant share of emissions is also from petroleum, has a residential share of 0.3 percent — the lowest in the U.S. because of minimal heating and cooling requirements. The largest sector emissions share in Hawaii, like Vermont, was from the transportation sector (49.3 percent). However, unlike Vermont, Hawaii’s electric power sector share nearly as high (40.1 percent). The dominant fossil fuel for the generation of electricity in Hawaii is petroleum.
Per capita carbon dioxide emissions
Another useful way to compare total carbon dioxide emissions across states is to divide them by state population and examine them on a per capita basis. Many factors contribute to the amount of emissions per capita, including: climate, the structure of the state economy, population density, energy sources, building standards and explicit state policies to reduce emissions.
The 2010 carbon dioxide emissions in Wyoming were 118.5 metric tons per capita, the highest in the U.S. In 2010, Wyoming was the second largest energy producer in the U.S. Unlike the largest energy producer, Texas, that has a population of 25 million, Wyoming has less than 600 thousand people giving Wyoming the lowest population density in the lower 48 states. Its winters are cold (the average low temperatures in January are in the 5 to 10 degree Fahrenheit range). These factors act to raise Wyoming’s per capita emissions compared to other states.
The second highest state per capita carbon dioxide emissions level was North Dakota at 80.4 metric tons per capita. Alaska (54.6 metric tons per capita), West Virginia (54.2 metric tons per capita) and Louisiana (49.3 metric tons per capita) round out the top five states in terms of per capita carbon dioxide emissions. All of these are fossil-energy-producing states. The activity of producing energy is itself energy intensive.
The State of New York, with a population of 19.6 million people, had the lowest per capita carbon dioxide emissions — 8.8 metric tons per capita. A large portion of the population is located in the New York City metropolitan area where mass transit is readily available and most residences are multi-family units that provide efficiencies of scale in terms of energy for heating and cooling.
The New York economy is oriented towards high-value, low-energy-consuming activities such as financial markets. For example, in 2010 New York contained 6.3 percent of the U.S. population, but consumed only 1.1 percent of the country’s industrial energy. New York’s energy prices are relatively high (the average retail electricity price of 16.41 cents per kWh was third highest in the country in 2010), which in turn encourages energy savings.
The second lowest per capita carbon emitting state (9.7 metric tons per capita) was Vermont. As mentioned above, Vermont had almost no emissions from its electric power sector. Other states with relatively low per capita emissions rates include: California (9.9 metric tons per capita), Idaho and Oregon (both 10.4 metric tons per capita).
The energy intensity of a state, as measured by the amount of energy consumed per unit of economic output or, specifically, British thermal units per dollar of a state’s gross domestic product (Btu/GDP), plays an important role in its overall emissions profile. The states with the highest rates of emissions per capita in 2010 also had the higher energy intensity values: Wyoming (24.6 thousand Btu per dollar), North Dakota (22.8 thousand Btu per dollar) and West Virginia (21.6 thousand Btu per dollar).
Delaware had the lowest energy intensity (3.3 thousand Btu per dollar), followed by New York (3.5 thousand Btu per dollar), Massachusetts, and Connecticut (both 3.7 thousand Btu per dollar). With the exceptions of California and Hawaii, the states with the lowest energy intensity are clustered in the relatively densely populated New England and Central-Atlantic. The 2010 national average is 7.5 thousand Btu per dollar of GDP.
Carbon intensity of energy supply
The carbon intensity of energy supply (CO2/Btu) is reflective of the energy fuel mix within a state. As with energy intensity, the states with high carbon intensity of energy supply tend to be the states with high per capita emissions. The top five states in 2010 for the energy carbon intensity as measured in kilograms of carbon dioxide per million Btu (kg CO2/MMBtu) — West Virginia (81.7 kg CO2/MMBtu), Kentucky (77.2 kg CO2/MMBtu), Wyoming (76.8 kg CO2/MMBtu), Indiana (75.1 kg CO2/MMBtu), and North Dakota (73.6 kg CO2/MMBtu)— are all states with coal as the dominant fuel.
The national average carbon intensity of the energy supply in 2010 was 57.6 kg CO2/MMBtu. The states with lower carbon intensity tend to be those states with relatively substantial non-carbon electricity generation such as hydropower or nuclear. These states include, for example, Vermont (34.5 kg CO2/MMBtu), Washington (37.4 kg CO2/MMBtu), Oregon (39.1 kg CO2/MMBtu), Idaho (41.2 kg CO2/MMBtu) and New Hampshire (41.5 kg CO2/MMBtu).
Carbon intensity of the economy
Another measure, the overall carbon intensity of the economy (CO2/dollar of state GDP), combines energy intensity with the carbon intensity of that energy supply. As one would expect, the states with the highest carbon intensity of their economies as measured in metric tons of carbon dioxide per million dollars of state GDP (mt CO2/million dollars of GDP) are also the states with the highest values of energy intensity and carbon intensity of that energy supply. In 2010 these states included: Wyoming (1,886 mt CO2/ million dollars of GDP), West Virginia (1,767 mt CO2/ million dollars of GDP) North Dakota (1,681 mt CO2/ million dollars of GDP), Louisiana (1,145 mt CO2/ million dollars of GDP), and Montana (1,098 mt CO2/ million dollars of GDP). The 2010 U.S. average is 430 mt CO2/ million dollars of GDP.
The states with the lowest carbon intensity of economic activity are also states that appear on the lower end of both energy intensity and the carbon intensity of that energy supply. These states include: New York (167 mt CO2/ million dollars of GDP), Connecticut (175 mt CO2/ million dollars of GDP), Delaware (209 mt CO2/ million dollars of GDP), Massachusetts (213 mt CO2/ million dollars of GDP), and California (214 mt CO2/ million dollars of GDP).
Because this analysis does not account for electricity trade, it is important to understand how much this can influence a state’s carbon dioxide emissions profile. The Net Electricity Trade Index indicates whether a state is self sufficient in the generation of electricity in a given year (a value of 1); is a net importer of electricity in a given year (a value of less than 1); or is a net exporter of electricity in a given year (a value greater than 1).
More than half of the 10 states with the highest per capita emissions the states are net exporters of electricity in at least some years. In particular, Wyoming, North Dakota, West Virginia and Montana are large electricity exporters of power produced predominantly with coal. New Mexico is also a net exporter of electricity. Oklahoma is a net exporter, but its dominant fuel is natural gas. Indiana is a small exporter in some years, but was export-neutral in 2009 and 2010. Kentucky, like Indiana is a coal-fueled generation state, but has been export-neutral in recent years. Louisiana, the only state of high per capita emitters that is consistently a net importer of electricity, and Alaska a state that is an importer in some years, but export-neutral in most, are both fossil-fuel producing states with a large energy-intensive component of their economies.
Four of the ten states with the lowest per capita carbon dioxide emissions are consistent importers of electricity: Idaho, California, Massachusetts, and Florida. Rhode Island was an electricity exporter in 2001 and was self-sufficient in 2000, 2008, 2009, and 2010. In the other years Rhode Island was an importer of electricity (about 40 percent in 2004). Idaho generates its electricity principally with hydroelectric power and has historically imported 50 percent or more of its electricity from other states. California consistently imports about 30 percent of its electricity and natural gas is the dominant fuel for the electricity that it generates internally. Both Massachusetts and Florida also use natural gas as the dominant fuel for electricity generation.
New York, which is self sufficient many years and a slight importer in other years, generates a dominant share of its electricity with nuclear power. Vermont, which is a consistent exporter of electricity, is also a state dominated by nuclear power generation. Connecticut, also a nuclear power producer, is a slight exporter in some years, an importer in others and self sufficient in yet others. Both Oregon and Washington are usually either self sufficient or net exporters. However, in 2001, which was a particularly bad year for hydroelectric generation in the Pacific Northwest, both states were net importers of electricity.
If the emissions associated with the generation of electricity were allocated to the states where that electricity is consumed, in many cases, the emissions profiles of both the producing and consuming states would change.