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Greenhouse Gas Overview

Congress is debating legislation to implement a federal cap and trade program for greenhouse gas emissions and create new energy development and energy efficiency initiatives. The proposed legislation would regulate emissions of greenhouse gases including carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, perfluorocarbons, nitrogen trifluoride and certain hydrofluorocarbons.

The following excerpt from the U.S. Environmental Protection Agency explains how greenhouse gases occur and describes emission trends:

Gases that trap heat in the atmosphere, thus making the Earth warmer, are often called greenhouse gases. 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:

  • Carbon Dioxide (CO2): Carbon dioxide enters the atmosphere through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of other chemical reactions (e.g., manufacture of cement). Carbon dioxide is also removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.
  • Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.
  • Nitrous Oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.
  • Fluorinated Gases: Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for ozone-depleting substances (i.e., CFCs, HCFCs, and halons). 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”).

Texas represents a large portion of the nation’s carbon dioxide (COX), sulphur dioxide (SO2) and nitrous oxide (NOX) emissions. EPA currently regulates the emissions of SO2 and NOX, so-called "criteria pollutants" under the Clean Air Act. Carbon dioxide regulation is a key focus in proposed federal legislation.

Texas Electric Utility, Commercial and Industrial Air Emissions, 2006
Emissions CO2
(Metric Tons)
(Metric Tons)
(Metric Tons)
Total U.S. Emissions 2,459,800,018 9,523,561 3,799,447
Total Texas Emissions 257,552,164 558,350 260,057
Texas Emissions as a Percent of U.S. 10.5% 5.9% 6.8%
Emissions from Coal in Texas 150,589,481 523,073 119,910
Percent of state emissions from coal 58.5% 93.7% 46.1%
Percent of U.S. emissions from coal in Texas 6.1% 5.5% 3.2%

Sources: U.S. Energy Information Administration and Comptroller of Public Accounts.

Emission Trends & Projections

Excerpt from Environmental Protection Agency

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 Fourth U.S. Climate Action Report concluded, in assessing current trends, that carbon dioxide emissions increased by 20 percent from 1990-2004, while methane and nitrous oxide emissions decreased by 10 percent and 2 percent, respectively. The declines in methane emissions are due to a variety of technological, policy, and agricultural changes, such as increased capture of methane from landfills for energy, reduced emissions from natural gas systems, and declining cattle populations. At least some of the decline in nitrous oxide emissions is due to improved emissions control technologies in cars, trucks, and other mobile sources. (Fourth U.S.Climate Action Report, 2007)

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.

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