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Greenhouse Gas Basics

Federal agencies must understand key terms and management basics to successfully manage greenhouse gas (GHG) emissions. Greenhouse gases are trace gases in the lower atmosphere that trap heat through a natural process called the "greenhouse effect." This process keeps the planet habitable. International research has linked human activities to a rapid increase in GHG concentrations in the atmosphere, contributing to major shifts in the global climate.

Graphic of the top half of earth depicting current arctic sea ice. A red outline depicts arctic sea ice boundaries in 1979. Current arctic sea ice is shown roughly 50% smaller than the 1979 depiction.
Greenhouse gases correlate directly to global warming, which impacts arctic sea ice. This image shows the arctic sea ice formation. The red outline depicts arctic sea ice boundaries in 1979.


Types of Greenhouse Gases

Greenhouse gases are defined in two categories; naturally occurring and manmade (also known as anthropogenic emissions). Ice core samples indicate that concentrations of naturally occurring GHGs have remained relatively steady for thousands of years (fluctuating within a range of 100 parts per million (ppm) of naturally occurring carbon dioxide over the last 400,000 years). Among others, these naturally occurring GHGs include:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous oxide (N2O).

Manmade greenhouse gases are a particular problem as they remain in the atmosphere for thousands of years and can be thousands of times more effective at trapping heat. Among others, these gases include:

  • Perfluorocarbons (PFCs)
  • Hydrofluorocarbons (HFCs)
  • Sulfur hexafluoride (SF6).

The six gases listed above were identified in Executive Order (E.O.) 13514 as the major contributors to global climate change. Other greenhouse gases exist, including nitrogen trifluoride (NF3), which is receiving increasing attention across the globe due to its high global warming potential.

Climate Change

Burning fossil fuels, increased agriculture, and deforestation all emit natural greenhouse gases and are concerning due to their contribution to increased concentrations of these greenhouse gases. Human activities also increase GHG emissions that are not naturally occurring in the atmosphere. These activities include semiconductor manufacturing, refrigerant leaks, and other industrial sources. The high level of greenhouse gases trap heat close to the surface of the earth, contributing to major shifts in the global climate.

The figure below shows common sources of natural and artificial greenhouse gases frequently employed by Federal agencies. These sources span three commonly used scopes.

  • Scope 1 includes greenhouse gas emissions from sources that are owned or controlled by a Federal agency.

  • Scope 2 includes greenhouse gas emissions resulting from the generation of electricity, heat, or steam purchased by a Federal agency.

  • Scope 3 includes greenhouse gas emissions from sources not owned or directly controlled by a Federal agency but related to agency activities, such as business travel and employee commuting.

Graphic depicting three the three scopes of greenhouse gas emissions. A cloud hovering at the top of the image represents the six greenhouse gases defined by the Kyoto Treaty (CO2, SF6, CH4, N2O, HFCs, PFCs,). Three scopes represented by pictures feed into the cloud. Pictures include power lines, nuclear facilities, central plants, a van, construction equipment, a car, industrial facilities, a bus, trash can, and an airplane. Each picture fits into one of three scopes.

Common sources of greenhouse gas emissions from Federal facilities typically fall into one of three scopes. Other greenhouse gases exist, but these six are called out by E.O. 13514.

* Additional significant Scope 3 sources exist beyond the examples provided

Climate change is often used interchangeably with global warming, but climate change is growing in preference because it conveys greenhouse gas impacts beyond rising temperatures. By definition, climate change refers to any significant change in measures of climate (e.g., temperature, precipitation, wind) lasting an extended period (decades or longer). Global warming is an average increase in lower atmosphere temperature that can contribute to changes in global climate patterns.

Greenhouse Gas Management

Effective management of greenhouse gas emissions is essential to reducing the Federal Government's contribution to global climate change. Managing greenhouse gas emissions involves several steps, including:

  • Creating an Inventory: GHG inventories establish a baseline of emissions produced by buildings, transportation, industrial processes, agriculture, and other energy consuming/producing activities. The baseline is typically expressed in tons of carbon dioxide equivalent or MTCO2e.

  • Setting Goals and Milestones: With a baseline established using inventory data, the next step is setting an end goal, whether it be a reduction of GHG emissions or complete climate neutrality. Milestones should be created to help track results to the end goal.

  • Creating a Strategic Greenhouse Gas Management Plan: GHG management, like all energy management activities, requires a thorough plan. Creating a comprehensive portfolio of emission reduction activities ensures targeting strategic reductions across all opportunities instead of a loose collection of one-off activities. Savings will be realized during the implementation phase.

  • Plan Implementation: Plans will not succeed if not implemented. During the implementation process, greenhouse gas management plans are often updated based on changes in mission and incremental findings and results.

  • Measurement and Verification: Projects must be measured and verified to ensure emission reduction measures meet planned milestones and goals. GHG inventories should also be verified to ensure accuracy and consistency across the Federal Government.

Greenhouse Gas Terminology*

  • Greenhouse Gases: Includes carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.

  • Scope 1 Emissions: Includes direct greenhouse gas emissions from sources that are owned or controlled by a Federal agency.

  • Scope 2 Emissions: Includes direct greenhouse gas emissions resulting from the generation of electricity, heat, or steam purchased by a Federal agency.

  • Scope 3 Emissions: Includes greenhouse gas emissions from sources not owned or directly controlled by a Federal agency but related to agency activities, such as vendor supply chains, delivery services, and employee travel and commuting.

  • Absolute Greenhouse Gas Emissions: Total greenhouse gas emissions without normalization for activity levels (see Energy Intensity) but including any allowable consideration for sequestration.

  • Renewable Energy: Energy produced by solar, wind, biomass, landfill gas, ocean (including tidal, wave, current, and thermal), geothermal, municipal solid waste, or new hydroelectric generation capacity achieved from increased efficiency or additions of new capacity at an existing hydroelectric project.

  • Energy Intensity: Energy consumption per square foot of building space, including industrial or laboratory facilities.

  • Excluded Vehicles and Equipment: Any vehicle, vessel, aircraft, or non-road equipment owned or operated by an agency of the Federal Government that is used in combat service or support, tactical or relief operations or training, Federal law enforcement, emergency response, or space flight vehicles.

  • Alternative Fuel Vehicles: Vehicles defined by Section 301 of the Energy Policy Act of 1992 as amended (42 USC 13211) and otherwise including electric-fueled and/or hybrid electric vehicles, plug-in hybrid electric vehicles, dedicated alternative fueled vehicles, dual-fueled alternative fueled vehicles, qualified fuel cell vehicles, advanced lean burn technology motor vehicles, self-propelled vehicles such as bicycles, and any other alternative fueled vehicles that are defined by statute.

*As defined by E.O. 13514