Global Warming Potentials
[FONT=Times,Times][FONT=Times,Times]Gases in the atmosphere can contribute to the greenhouse effect both directly and indirectly. Direct effects occur when the gas itself absorbs radiation. Indirect radiative forcing occurs when chemical transformations of the substance produce other greenhouse gases, when a gas influences the atmospheric lifetimes of other gases, and/or when a gas affects atmospheric processes that alter the radiative balance of the earth (e.g., affect cloud formation or albedo).[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]6 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]The IPCC developed the Global Warming Potential (GWP) concept to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to another gas.[/FONT]
[FONT=Times,Times]The GWP of a greenhouse gas is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kilogram (kg) of a trace substance relative to that of 1 kg of a reference gas (IPCC 2001). Direct radiative effects occur when the gas itself is a greenhouse gas. The reference gas used is CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times], and therefore GWP-weighted emissions are measured in teragrams (or million metric tons) of CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]equivalents (Tg CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Eq.).[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]7,8 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]All gases in this Executive Summary are presented in units of Tg CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Eq. [/FONT]
[/FONT]The UNFCCC reporting guidelines for national inventories were updated in 2006,[FONT=Times,Times][FONT=Times,Times]9 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]but continue to require the use of GWPs from the IPCC Second Assessment Report (SAR) (IPCC 1996). This requirement ensures that current estimates of aggregate greenhouse gas emissions for 1990 to 2007 are consistent with estimates developed prior to the publication of the IPCC Third Assessment Report (TAR) and the IPCC Fourth Assessment Report (AR4). Therefore, to comply with international reporting standards under the UNFCCC, official emission estimates are reported by the United States using SAR GWP values. All estimates are provided throughout the report in both CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]equivalents and unweighted units. A comparison of emission values using the SAR GWPs versus the TAR and AR4 GWPs can be found in Chapter 1 and, in more detail, in Annex 6.1 of this report. The GWP values used in this report are listed in Table ES-1.[/FONT]
[/FONT][FONT=Times,Times][FONT=Times,Times]6 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Albedo is a measure of the Earth’s reflectivity, and is defined as the fraction of the total solar radiation incident on a body that is reflected by it.[/FONT]
[/FONT][FONT=Times,Times][FONT=Times,Times]7 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Carbon comprises 12/44[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]ths [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]of carbon dioxide by weight.[/FONT]
[/FONT][FONT=Times,Times][FONT=Times,Times]8 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]One teragram is equal to 10[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]12 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]grams (g) or one million metric tons.[/FONT]
[/FONT][FONT=Times,Times][FONT=Times,Times]9 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]See <http://unfccc.int/resource/docs/2006/sbsta/eng/09.pdf>.[/FONT]
[/FONT][FONT=Times,Times][FONT=Times,Times]Global warming potentials are not provided for CO, NO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]x[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times], NMVOCs, SO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times], and aerosols because there is no agreed-upon method to estimate the contribution of gases that are short-lived in the atmosphere, spatially variable, or have only indirect effects on radiative forcing (IPCC 1996).[/FONT][/FONT]
ES.2. Recent Trends in U.S. Greenhouse Gas Emissions and Sinks
[FONT=Times,Times][FONT=Times,Times]In 2007, total U.S. greenhouse gas emissions were 7,150.1 Tg CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Eq. Overall, total U.S. emissions have risen by 17 percent from 1990 to 2007. Emissions rose from 2006 to 2007, increasing by 1.4 percent (99.0 Tg CO[/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]2 [/FONT][/FONT][FONT=Times,Times][FONT=Times,Times]Eq.). The following factors were primary contributors to this increase: (1) cooler winter and warmer summer conditions in 2007 than in 2006 increased the demand for heating fuels and contributed to the increase in the demand for electricity, (2) increased consumption of fossil fuels to generate electricity and (3) a significant decrease (14.2 percent) in hydropower generation used to meet this demand.[/FONT]
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[FONT=Times,Times][FONT=Times,Times]Table ES-1: Global Warming Potentials (100-Year Time Horizon) Used in This Report[/FONT]
[FONT=Times,Times][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]Gas [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]GWP[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]CO[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]1[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]CH[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]4[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]* - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]21[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]N[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]O - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]310[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-23 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]11,700[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-32 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]650[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-125 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2,800[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-134a - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]1,300[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-143a - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]3,800[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-152a - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]140[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-227ea - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2,900[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-236fa - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]6,300[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]HFC-4310mee - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]1,300[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]CF[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]4 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]6,500[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]C[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]F[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]6 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]9,200[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]C[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]4[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]F[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]10 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]7,000[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]C[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]6[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]F[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]14 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]7,400[/FONT][/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]SF[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]6 - [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]23,900[/FONT][/FONT]
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[FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]Source: IPCC (1996)[/FONT]
[FONT=Swiss 72 1 BT,Swiss 72 1 BT]* The CH[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]4 [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]GWP includes the direct effects and those indirect effects due to the production of tropospheric ozone and stratospheric water vapor. The indirect effect due to the production of CO[/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]2 [/FONT][/FONT][FONT=Swiss 72 1 BT,Swiss 72 1 BT][FONT=Swiss 72 1 BT,Swiss 72 1 BT]is not included.[/FONT][/FONT]
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