Overview
Energy-related carbon dioxide (CO2) emissions vary significantly across states, whether considered on an absolute basis (Figure 1) or on a per capita basis. Total state CO2 emissions include those from direct fuel use across all sectors, including residential, commercial, industrial, and transportation, as well as primary fuels consumed for electricity generation.
The physical size of a state, as well as the available fuels, types of businesses, climate, and population size and density, all play a role in determining the level of both total and per capita emissions. In addition, each state’s energy system reflects circumstances specific to that state. For example, some states have abundant hydroelectric supplies, while others contain abundant coal resources.This paper examines the factors that contribute to a state’s CO2 profile. The analysis does not attempt to assess the effect of state policies on absolute emissions levels, or on current and future trends, nor does it intend to imply that certain policies would be appropriate for a particular state.
The term energy-related CO2 emissions, as used in this analysis, includes emissions released at the location where fossil fuels are combusted. To the extent that fuels are used in one state to generate electricity consumed in another state, emissions are attributed to the state in which electricity is generated and fuels are combusted. Attributing emissions to the state consuming the electricity, rather than the state where it is generated, would yield different results. For feedstock uses of fossil fuels, carbon stored in products such as plastics is subtracted from reported emissions for the states where they are produced.
The calculations presented in this paper also assume that biomass used by electricity generators, by industries, and by homes and commercial buildings is carbon neutral, with combustion emissions fully offset by land sinks in a sustainable biomass cycle. Emissions may be underestimated to the extent that actual use of biomass energy is not carbon neutral.
Total state emission levels
From 2000 to 2015, CO2 emissions fell in 41 states and rose in 9 states (not including the District of Columbia) (Table 1). The greatest percentage decrease was Maine’s 25%—a drop of 6 million metric tons (mt)—while the greatest absolute decline was 52 million mt in Ohio (a 19% reduction). Nebraska’s 22% rise in emissions—an increase of 9 million mt—was the largest in both absolute and percentage terms between 2000 and 2015.
From 2014 to 2015, 31 states saw a decrease in emissions, while 18 experienced an increase—Oregon’s emissions were unchanged. Over that period, national emissions decreased by about 2.7%. Because of differences in how the national and state data sets are collected and presented, it is not possible to directly compare the total for all states with the total for the United States. See Appendix A for a comparison of the state- and national-level data systems.Emissions by fuel
States exhibit very different emissions profiles by fuel type (Table 2). For example, in 2015, coal consumption accounted for 75% of energy-related CO2 emissions (69 million mt) in West Virginia and 71% of Wyoming’s energy-related CO2 emissions (46 million mt). In California, where less than 1% of CO2 emissions came from coal (3 million mt), 64% came from petroleum (234 million mt). In Rhode Island, which had no emissions from coal, 53% of CO2 emissions were from petroleum (6 million mt). Hawaii’s and Vermont’s shares of CO2 emissions from petroleum in 2015 were 92% (17 million mt) and 89% (5 million mt), respectively. Maine’s petroleum share was 81% (14 million mt). No other state’s petroleum share exceeded 70%.
Emissions by sector
CO2 emissions also vary significantly by sector (Tables 3 and 4), based on factors such as the use of different fuels for electricity generation, different climates, and different sources of economic outputs (e.g., commercial versus industrial activity). For example, in Vermont, the largest share of emissions in 2015 came from the transportation sector (55%, or 3 million mt), predominantly from petroleum, while the electric power sector share rounded to 0.0% because Vermont had virtually no reported generation using fossil fuels. Vermont’s residential sector share (23%, or 1.4 million mt) reflected its relatively cold climate where petroleum is the main heating fuel. On the other hand, Hawaii, where a dominant share of emissions is also from petroleum, had a residential share of 0.2% (0.03 million mt) and the lowest in the United States because of its minimal heating fuel requirements. The largest sector emissions share in Hawaii, like Vermont, was from the transportation sector (54%, or 10 million mt). However, unlike Vermont, Hawaii’s electric power sector share was relatively high (36%, or 7 million mt) because petroleum is the dominant fossil fuel generating electricity in Hawaii.
Per capita carbon dioxide emissions
Another useful way to compare total CO2 emissions across states is to divide them by state population and examine them on a per capita basis (Table 5 and Figure 2). Many factors contribute to variation in 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 2015 CO2 emissions in Wyoming were 110 mt per capita, the highest in the United States. In 2015, Wyoming was the second-largest energy producer in the United States. Unlike the largest energy producer, Texas, with a population of 27 million, Wyoming has fewer than 600,000 people, giving Wyoming the lowest population density in the Lower 48 states. Its winters are cold (the average low temperatures in January range between 5 to 10 degrees Fahrenheit). These factors raise Wyoming’s per capita emissions compared with other states. The second-highest state per capita CO2 emissions level was North Dakota at 75 mt per capita. West Virginia (50 mt per capita), Alaska (49 mt per capita), and Louisiana (47 mt per capita) round out the top five states in terms of per capita CO2 emissions.
New York, with a population of almost 20 million people, had the lowest per capita CO2 emissions of any state—fewer than 9 mt 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 used for heating and cooling. The New York economy is oriented towards low energy-consuming activities such as financial markets; for example, New York accounted for about 6% of the U.S. population in 2015, but consumed only 1% of the country’s industrial energy.3 New York’s energy prices are relatively high (the average retail electricity price of 15.28 cents per kWh was eighth highest in the country in 2015), which in turn encourages energy savings.4Other states with fewer than 10 mt per capita include California, Maryland, Massachusetts, Oregon, and Vermont. Connecticut and Rhode Island produce slightly more than 10 mt of CO2 per capita. The national average is 16 mt per capita.
Energy intensity
The energy intensity of a state, as measured by the amount of energy consumed per unit of economic output or, specifically, British thermal units (Btu) per dollar of a state’s gross domestic product (GDP), plays an important role in its overall emissions profile (Table 6). The states with the highest rates of emissions per capita in 2015 also tended to have higher energy-intensity values: Wyoming (24,000 Btu per chained 2009 dollar of GDP), Louisiana (20,000 Btu per dollar), West Virginia (19,000 Btu per dollar), North Dakota (16,000 Btu per dollar), and Montana and Alabama (both about 14,000 Btu per dollar). California, Connecticut, Maryland, Massachusetts, and New York were the lowest—each at about 3,000 Btu per dollar. Many of the states with the lowest energy intensities are clustered in the relatively densely populated New England and Middle Atlantic regions. The 2015 national average was 6,000 Btu per dollar of GDP.
Carbon intensity of the energy supply
The carbon intensity of energy supply (CO2/Btu) reflects the energy fuel mix within a state (Table 7). As with energy intensity, the states with high carbon intensity of energy supply tend to be the states with high per capita emissions. The states with the most carbon-intensive energy supply as measured in kilograms of CO2 per million Btu (kg CO2/MMBtu)—West Virginia (79 kg CO2/MMBtu), Wyoming (77 kg CO2/MMBtu), Kentucky (74 kg CO2/MMBtu), Utah (72 kg CO2/MMBtu), and Indiana and North Dakota (both about 70 kg CO2/MMBtu)—are all states with coal as the dominant emissions source (Table 2). The national average carbon intensity of the energy supply in 2015 was 55 kg CO2/MMBtu. The states with lower carbon intensity of their energy supply tend to be those states with relatively substantial non-carbon electricity generation such as nuclear or hydropower. These states include Washington (36 kg CO2/MMBtu), Vermont and Oregon (both 37 kg CO2/MMBtu), New Hampshire (39 kg CO2/MMBtu), and Maine and South Dakota (both 40 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 state’s energy supply. As expected, the states with the highest carbon intensity of their economies (Table 8) as measured in metric tons (mt) of CO2 per million dollars of state GDP (mt CO2/million chained 2009 dollars of GDP) are also the states with the highest values of energy intensity and carbon intensity of that energy supply. In 2015, these states included: Wyoming (1,814 mt CO2/million dollars of GDP), West Virginia (1,371 mt CO2/million dollars of GDP), North Dakota (1,122 mt CO2/million dollars of GDP), Louisiana (1,055 mt CO2/million dollars of GDP), and Montana (786 mt CO2/million dollars of GDP). The 2015 U.S. average was 320 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 (133 mt CO2/million dollars of GDP), Massachusetts (150 mt CO2/million dollars of GDP), Connecticut (160 mt CO2/million dollars of GDP), California (163 mt CO2/million dollars of GDP), and Maryland (181 mt CO2/million dollars of GDP).
Electricity trade
This analysis assigns all emissions related to the primary energy consumed for the production of electricity to the state where that electricity is produced rather than where it is consumed. As a result, the states that produce electricity from fossil fuels (especially coal) and sell that electricity across state lines tend to have higher per capita CO2 emissions than states that consume more electricity than they produce (Table 9). If the emissions associated with the generation of electricity were allocated to the states where that electricity is consumed, the emissions profiles of both the producing and consuming states would be different in many cases.
Non-carbon energy
Historically, the primary non-carbon-producing energy forms have been nuclear and hydroelectric generation. Neither energy form has experienced significant capacity increases in the United States in recent years. On the other hand, nonhydropower renewable energy forms such as wind and solar have experienced significant growth over the past decade, which has changed the non-carbon generation profile of several states.
Although California increased its electricity generated by wind and solar between 2000 and 2015 (Figure 3), generation from hydropower and nuclear fell between 2000 and 2015. In total, California non-carbon electricity generation fell from 78 billion kilowatthours (kWh) in 2000 to 59 billion kWh in 2015. Illinois increased its nuclear output from existing nuclear capacity while adding wind capacity and in 2015, the state produced 108 billion kWh from non-carbon generation sources. Pennsylvania experienced a pattern similar to that in Illinois. In contrast, Texas has more than doubled its non-carbon generation output over that period, from 39 billion kWh in 2000 to 86 billion kWh in 2015. This doubling resulted from a stable level of nuclear generation and additions of wind capacity. Washington State has always relied heavily on hydropower generation and has added wind capacity to its generation mix, which helped during the relatively low precipitation year in 2015.
See Appendix B for other EIA state-related energy and environmental products.
Footnotes
1U.S. Energy Information Administration, State Profiles and Energy Estimates: http://www.eia.gov/state/.
2http://www.wrcc.dri.edu/narratives/WYOMING.htm.
3U.S. Energy Information Administration, State Energy Data 2015, state population and energy consumption by sector.
4U.S. Energy Information Administration, State Electricity Profiles, Table 1, 2015 Summary Statistics http://www.eia.gov/electricity/state/newyork/.