(See endnote 15)

Greenhouse gases are gases that trap heat in the atmosphere, thereby not letting the heat flow back into space and warming the Earth’s surface. They include carbon dioxide (84% of the total), methane (9% of the total), nitrous oxide (5% of the total), and fluorinated gases (2% of the total).

Carbon dioxide is produced during the burning of coal, natural gas, oil, solid waste, trees, and wood products, and through certain chemical reactions such as during the production of cement. Carbon dioxide is sequestered or removed from the atmosphere when it is absorbed by plants and trees. (The destruction of forests greatly affects the amount of carbon dioxide in the air.)

Methane is found during the mining, processing, and transportation of coal, natural gas, and oil. It is also emitted by cattle and by organic waste decaying in municipal solid waste landfills. (The largest methane emitters are China, India, the United States, Brazil, Russia, Mexico, Ukraine, and Australia, which account for about half of all of the anthropogenic methane emissions in the world. The largest source of methane emissions in the United States is landfills.) The global warming potential of methane is very large, since it is 25 times greater than carbon dioxide. Methane contributes more than one third of today’s global warming caused by people.

Nitrous oxide is produced by agricultural activities, industrial activities, and the burning of fossil fuels and solid waste.

Fluorinated gases, regulated by the Montreal Protocol and the Kyoto Protocol, come from industrial processes either as a final product or as a byproduct. Although they are released in small quantities, they have a very potent effect on global warming. Since chlorofluorocarbons deplete the ozone layer in the atmosphere, they had been replaced with hydrofluorocarbons, which are strong greenhouse gases. This is a prime example of trying to correct one environmental problem while causing another one. Sulfur hexafluoride is another potent greenhouse gas which is used primarily to insulate electrical equipment, since it is non-combustible and non-flammable. Leakage of the gas as well as emissions during equipment maintenance exacerbate warming trends in the area where this material is used.

Each of the greenhouse gases affect climate change depending on their concentration in the air, how long they stay in the atmosphere, and how effective they are in producing global warming. Some gases can remain in the atmosphere for many years. It should be recognized that even after there has been a substantial reduction in greenhouse gases, that the full effect of the emissions will be felt for many years into the future because of lag time. Water heats more slowly than the atmosphere and the greenhouse gases that have been trapped in the ocean will be released slowly over time back to the atmosphere.

Although ozone depletion is not a major cause of climate change, it still has some effect on the temperature balance of the earth. Atmospheric ozone absorbs solar ultraviolet radiation which heats the stratosphere. It also absorbs infrared radiation from the surface of the earth, which traps heat in the troposphere. Whereas ozone losses in the lower stratosphere from chlorine and bromine- containing gases cool the Earth’s surface, surface pollution gases rising in to the troposphere can heat the Earth’s surface thereby contributing to the greenhouse effect. (See endnote 80.)

General Best Practices for Land and Forests (See endnote 24)

  • • Increase or maintain carbon storage by transforming cropland into forest areas.
  • • Avoid destroying forest land.
  • • Reduce soil erosion in forests and farmlands to minimize soil losses which affects soil carbon storage.
  • • Plant appropriate vegetation that will grow rapidly on land where the soil has been disturbed and soil erosion has occurred.
  • • Encourage the growth of green areas in urban and suburban situations.

Sources of Greenhouse Gases

(See endnotes 23, 81)

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