Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases ('High GWP gases').Įach gas's effect on climate change depends on three main factors:Ĭoncentration, or abundance, is the amount of a particular gas in the air. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons).

Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes.

Nitrous oxide (N 2O): Nitrous oxide is emitted during agricultural, land use, industrial activities, combustion of fossil fuels and solid waste, as well as during treatment of wastewater.

Methane emissions also result from livestock and other agricultural practices, land use and by the decay of organic waste in municipal solid waste landfills.

Methane (CH 4): Methane is emitted during the production and transport of coal, natural gas, and oil.

Carbon dioxide is removed from the atmosphere (or 'sequestered') when it is absorbed by plants as part of the biological carbon cycle.

Carbon dioxide (CO 2): Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of cement).

Inventory and the IPCC's discussion on GWPs (PDF) (106 pp, 7.7MB). For further discussion of GWPs and an estimate of GHG emissions using updated GWPs, see Annex 6 of the U.S. Inventory, which are drawn from the IPCC’s Fourth Assessment Report (AR4). The GWP values appearing in the Emissions webpages reflect the values used in the U.S. The GWP takes into account the fact that many gases are more effective at warming Earth than CO 2, per unit mass. To convert emissions of a gas into CO 2 equivalent, its emissions are multiplied by the gas's Global Warming Potential (GWP). GHG emissions are often measured in carbon dioxide (CO 2) equivalent.

For reference, a metric ton is a little bit larger (about 10%) than a U.S. Inventory uses metric units for consistency and comparability with other countries. Thus, a million metric tons is roughly the same mass as 1 million small cars! For comparison, a small car is likely to weigh a little more than 1 metric ton. 6,457 million metric tons of CO 2: What does that mean?Ī million metric tons is equal to about 2.2 billion pounds, or 1 trillion grams.

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