Monday, August 24, 2009

Overview: Greenhouse Gasses

greenhouse-gas.jpgThe heart of climate change is the greenhouse gas effect. Molecules of various gasses trap heat, causing the atmosphere to heat up. Some of these gasses are okay and normal, but when there is too much it creates too much heat. Too much heat throws the whole system out of balance. What makes a gas a greenhouse gas is that it traps heat. (image courtesy ZooFari from Wikimedia Commons)

Some of the gasses (such as carbon dioxide) are part of natural processes (such as breathing) leading to erroneous claims of harmlessness. The same gasses can be emitted by non-natural processes (such as burning fossil fuel) which are not at all harmless. It's one thing for a gas to come from a natural process, it's quite another thing for it to come from an unnatural one. The natural world designed itself to accomodate naturally occuring quantities of various gasses, and human activity to add additional quantities of these gasses throws the system out of balance.

The principal greenhouse gases that enter the atmosphere because of human activities are (courtesy EPA):

  • Carbon Dioxide (CO2): Carbon dioxide enters the atmosphere by 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”).

A greenhouse gas inventory is an accounting of the amount of greenhouse gases emitted to or removed from the atmosphere over a specific period of time (e.g., one year). A greenhouse gas inventory also provides information on the activities that cause emissions and removals, as well as background on the methods used to make the calculations.