Our ability to harness ever-expanding amounts of data is completely transforming our understanding of environmental problems and solutions. Our Climate Insights blog series  leverages data from CAIT 2.0 , WRI’s climate data explorer, to shed light on the many dimensions of climate change that shape society, policy, and global development.
The U.S. Environmental Protection Agency recently announced  a carbon dioxide pollution standard that sets state-based targets  for power sector greenhouse gas (GHG) emissions out to 2030. The new EPA standard gives states flexibility  in how they meet the emissions standard by letting them reduce emissions  in ways that work for their power sectors.
But where do U.S. power sector emissions come from? And how have they changed over time? Today, WRI released an update of its U.S. state GHG emissions data  via CAIT 2.0, our climate data explorer. These and other data can provide valuable context for the proposed standard by helping to answer questions about emissions from the U.S. power sector and other sources, as well as related historic developments.
How Have U.S. Power Sector Emissions Changed in the Last 40 Years?
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The CAIT 2.0 U.S. data, together with data from the U.S. Energy Information Administration (EIA) 1, show the historic trend of power sector CO₂ emissions. Between 1973 and 2005, U.S. power sector CO₂ emissions increased by almost 90 percent. However, after emissions nearly stabilized between 2005 and 2007, the United States reversed the trend of rising CO₂ emissions in recent years.
Many drivers have contributed to this decline, including  fuel-switching from coal to natural gas, new renewable energy generation, reduced power consumption as a result of the economic downturn, new vehicle rules , and state energy efficiency policies . However, these trends likely won’t suffice to further decrease emissions. Current projections suggest  that without future policy actions (such as the proposed EPA power plant standard ), power sector CO₂ emissions are expected to increase slowly again.
What Does the Power Sector Contribute to U.S. Emissions?
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The power sector comprises the largest share of U.S. GHG emissions, contributing nearly one-third of all emissions from all sectors. For the United States to meet its economy-wide emissions-reduction pledge of 17 percent below 2005 by 2020 , cuts in power sector emissions are essential. WRI’s analysis has already shown  that the power sector represents the biggest opportunity to cut GHG emissions.
What Does Each State Contribute to U.S. Power Sector Emissions?
Power sector emissions vary considerably among U.S. states. To highlight some of these differences, the left map shows that states that rely largely on fossil fuels, have large industrial sectors, and/or have relatively large populations—such as Texas, Florida, and the states of the Midwest—currently contribute the most power sector emissions. In comparison, the map on the right shows power sector emissions per person . Here, states that produce power from fossil fuels but have relatively small populations are the largest contributors. Notably, however, the emissions figures in both maps only consider the production of power within each state, although that power may be consumed by out-of-state businesses and homes.
How Much Does Each State’s Power Sector Contribute to Its Total Emissions?
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The emissions landscape within states can be diverse. The graph above shows the percentage of state GHG emissions that come from the power sector (in blue). Emissions contributions from the power sector vary from nearly 60 percent for Wyoming to less than 2 percent in Idaho and Vermont, which generate most their electricity from hydro and nuclear power plants, respectively.
How Have State Power Sector Emissions Changed Since 2005?
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Cutting power sector emissions is not new at the state level. According to the 2011 U.S. data available through CAIT 2.0, 42 states reduced their emissions  relative to 2005, the baseline used in the U.S. GHG reduction pledge. The graph above shows the 10 states with the most significant reductions. All of them reduced their power sector GHG emissions by more than 30 percent in just six years. Many of these states are also part of the Regional Greenhouse Gas Initiative , a cooperative market-based program to reduce emissions.
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For the top 10 emitters, shown in the graph above, the results are more variable. While Ohio, West Virginia, Florida and Indiana were able to reduce power sector emissions by more than 10 percent between 2005 and 2011, other large emitters, like Texas and Kentucky, slightly increased their emissions during this time period. WRI analysis shows  the existing policy and infrastructure opportunities some states can take to reduce their power sector emissions.
How Are the Sources of U.S. Power Sector Emissions Changing?
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The coming years will be a crucial time for power sector decision-makers to make choices about how power will be generated in the decades to come, as a significant fraction of existing U.S. power plants are approaching the end of their useful life. At the end of 2012, around 51 percent  of all generating capacity was more than 30 years old. While most gas-fired capacity is fewer than 20 years old, 74 percent of coal-fired power plants are older than 30 years (see figure, above). As a result, the EIA projects  that nearly 60 Gigawatts – or more than one-sixth – of coal-fired power capacity will retire between 2010 and 2020.
Explore More State-Level Emissions Data
The U.S. GHG emissions dataset available through CAIT 2.0 , as well as data provided by the EIA and other organizations, provide critical context for evaluating and understanding the proposed EPA standard  and other domestic climate policy initiatives. Good data and smart policies can help the United States cost-effectively reduce its emissions to achieve its 2020 reduction target and go even further in the post-2020 era.
- LEARN MORE: CAIT 2.0  offers many functions to quickly compare emissions, perform analysis, and create your own visualizations. CAIT’s U.S. state level data set  is now updated with 2011 emissions and covers all greenhouse gases, economic sectors and energy sub-sectors. Stay tuned for further updates and analysis by signing up for our newsletter.
Data Source: EIA, Monthly Energy Review June 2014, Available at: http://www.eia.gov/environment/data.cfm#summary ↩