Energy-related carbon dioxide (CO₂) emissions fell in 37 states between the years 2000–2013, according to an October report from the U.S. Energy Information Administration (EIA). CO₂ emissions rose in 13 states in the same time period. CO₂ emissions vary greatly across states, including on an absolute and per capita basis.


Maine experienced the greatest emissions decrease, at 27 percent, or 6 million metric tons. New York saw the greatest absolute decline, at 25 percent, or 52 million metric tons. Nebraska was the state with both the greatest percentage and absolute increase in CO₂ emissions, at 28 percent, or 11 million metric tons, according to the report.


CO₂ emissions also fell in 16 states from 2012 to 2013. During the same time period, 34 states experienced an increase in emissions. Emissions for 2013 increased by about 2.5 percent nationally. There are different methods for data aggregation among states and the national total, so the EIA warns that it is difficult to compare the total emissions for all states with the U.S. total.


The EIA releases an annual report on energy-related emissions levels. The October report finds that a state’s total CO₂ emissions are determined by its size, available fuels, types of businesses, climate and population density. Total state CO₂ emissions include direct fuel use across sectors, including commercial, industrial, residential and transportation as well as primary fuels consumed for electric generation, according to the report. CO₂ emissions also vary by sector, due to the use of different fuels for electricity generation, climate and other economic output.


Some states have hydroelectric supplies, while others have more coal resources, the report states. These types of supplies and resources affect a state’s energy system and emissions output. The EIA found that states have different emissions profiles based on fuel type. In 2013, coal consumption accounted for 78 percent of CO₂ emissions in West Virginia, and, in California, 1 percent of CO₂ emissions came from coal and 62 percent came from petroleum.


The EIA assigned all emissions related to primary energy consumed to the state where that electricity is produced, instead of where it’s consumed. So, states that produce electricity from fossil fuels and sell it across state lines can have higher per capita CO₂ emissions than states that consume more electricity than they produce.