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Greenhouse Gas Emissions

Greenhouse Gas Emissions Overview | Inventories | Projections | Project Methodologies

2011 Inventory of Greenhouse Gas Emissions and Sinks

Prepared annually by EPA, the national greenhouse gas inventory report presents estimates of U.S. greenhouse gas emissions and sinks for the years 1990 through 2009. This report also discusses the methods and data used to calculate the emission estimates.

Greenhouse Gas Overview

Gases that trap heat in the atmosphere are often called greenhouse gases. This section of the EPA Climate Change Site provides information and data on emissions of greenhouse gases to Earth’s atmosphere, and also the removal of greenhouse gases from the atmosphere. For more information on the science of climate change, please visit EPA's climate change science home page.

Some greenhouse gases such as carbon dioxide occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases (e.g., fluorinated gases) are created and emitted solely through human activities. The principal greenhouse gases that enter the atmosphere because of human activities are:

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Greenhouse Gas Inventories

A greenhouse gas inventory is an accounting of the amount of greenhouse gases emitted to or removed from the atmosphere over a specific period of time (e.g., one year). A greenhouse gas inventory also provides information on the activities that cause emissions and removals, as well as background on the methods used to make the calculations. Policy makers use greenhouse gas inventories to track emission trends, develop strategies and policies and assess progress. Scientists use greenhouse gas inventories as inputs to atmospheric and economic models.

To track the national trend in emissions and removals since 1990, EPA develops the official U.S. greenhouse gas inventory each year. The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change Exit EPA Disclaimer.

In addition to the U.S. inventory, greenhouse gas emissions can be tracked at the global, state and local levels as well as by companies and individuals:

The Intergovernmental Panel on Climate Change (IPCC) Exit EPA Disclaimer publishes internationally accepted inventory methodologies that serve as a basis for all greenhouse gas inventories, ensuring that they are comparable and understandable. The 2006 IPCC Guidelines Exit EPA Disclaimer were completed and accepted by the IPCC in May 2006.

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Emission Trends & Projections

Estimates of future emissions and removals depend in part on assumptions about changes in underlying human activities. For example, the demand for fossil fuels such as gasoline and coal is expected to increase greatly with the predicted growth of the U.S. and global economies.

The Fifth U.S. Climate Action Report concluded, in assessing current trends, that greenhouse gas emissions increased by 17 percent from 1990-2007. Over that same time period, the U.S. GDP increased by 65 percent and population increased by 21 percent. The dominant factor affecting U.S. emissions trends is CO2 emissions from fossil fuel combustion, which increased by 21.8 percent over the 17-year period, while methane and nitrous oxide emissions decreased by 5 percent and 1 percent, respectively. The declines in methane emissions are mostly due to increased collection and combustion of landfill gas, as well as improvements in technology and management practices at natural gas plants. The decline in nitrous oxide emissions is largely due to the installation of newer N2O control technologies in motor vehicles throughout the past decade. Fluorinated substances (HFCs, PFCs, and SF6) accounted for 2 percent of total U.S. GHG emissions in 2007. The increasing use of these compounds since 1995 as substitutes for ozone depleting substances has been largely responsible for their upward emissions trends. (Fifth U.S.Climate Action Report, 2010)

Many, but not all, human sources of greenhouse gas emissions are expected to rise in the future. This growth may be reduced by ongoing efforts to increase the use of newer, cleaner technologies and other measures. Additionally, our everyday choices about such things as commuting, housing, electricity use and recycling can influence the amount of greenhouse gases being emitted.

The United States government prepares projections of emissions and removals of all greenhouse gases. The following links provide more detailed information on projections:

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Project Methodologies

EPA has developed several Climate Leaders Offset Project Methodologies that use a standardized approach to determine project eligibility, address additionality, select and set the baseline, identify monitoring options, and quantify reductions.  This approach seeks to ensure that the GHG emission reductions from offset projects meet four key accounting principles—they must be real, additional, permanent, and verifiable.   

To be eligible as offsets, project activities must be surplus to regulation.  Projects are also required to demonstrate additionality by achieving a level of performance with respect to emission reductions and/or removals that is significantly better than business-as-usual.  Business-as-usual is determined from similar, recently undertaken or planned practices, activities or facilities in the same geographic region.  This level of “performance” may be defined as an emissions rate, a technology standard or a practice standard.  Data used in setting the performance standard is primarily collected from publicly available historic data (although planned or projected activities may be used in certain cases as well).  The performance standard approach minimizes the risk of accepting a project that is not additional or rejecting a project that is additional.  A performance standard approach also reduces the complexity, cost, and subjectivity of constructing individual project-specific reviews.

Performance standards are available for the following project types:

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