Greenhouse Gases and Global Warming

Naturally occurring and manmade gases that trap heat in the Earth's atmosphere, contributing to the "greenhouse effect" and global warming.

Greenhouse gases are gases that trap heat in the Earth's atmosphere by absorbing and re-emitting solar radiation. A buildup of greenhouse gases is causing the Earth's climate to change, most notably causing the atmosphere's total temperature to increase, an effect called global warming. The most important greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor, all of which occur naturally but are also manmade, plus a series of gases made solely by humans, which include sulfur hexafluoride (SF6), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs). (The Intergovernmental Panel on Climate Change (IPCC) offers a longer list of greenhouse gases.)

When sunlight and ultraviolet radiation hit the Earth and its atmosphere, most of it is reflected back into outer space, thanks to the ozone layer, clouds, and ice on the Earth's surface. But approximately 25 percent is absorbed by the planet and re-emitted as infrared radiation. Greenhouse gases in the atmosphere absorb some of this re-emitted radiation, and return it to the planet in the form of heat-this is called the "greenhouse effect." Because greenhouse gases in the air have increased, so has the amount of infrared radiation being trapped and re-emitted as heat. The U.N. Framework Convention on Climate Change website offers an excellent diagram of how the greenhouse effect works, that shows radiation from the sun becoming trapped under an increasingly thick "blanket" of gases.

Key Greenhouse Gases

Carbon dioxide is one of the greenhouse gases about which scientists are most concerned, mostly because human activities have caused its release into the atmosphere to greatly increase. Carbon dioxide enters the atmosphere through the burning of solid waste, wood, and fossil fuels including oil, natural gas, and coal. It is also created when cement is manufactured. Carbon dioxide is removed from the atmosphere or "sequestered" naturally by plants, but currently not enough to offset its production, which makes large-scale deforestation a matter of grave concern.

Nitrous oxide also enters the atmosphere when fossil fuels and solid wastes are burned, and is emitted during agricultural and industrial activities. Nitrous oxide is 270 times more effective at warming the atmosphere than carbon dioxide, although it is present in lower quantities.

Methane is emitted during the production and transport of oil, natural gas, and coal, as well as from livestock and rotting organic waste in landfills. Methane traps over 21 times more heat than carbon dioxide, but is also present in lower quantities.

Fluorinated gases including hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are completely manmade and generated through various industrial processes. Although they are typically emitted in lower quantities, they are highly potent with regards to global warming.

While CO2 currently contributes the most to the greenhouse effect, the other gases combined will soon be as important, given their increasing concentrations in the atmosphere and higher rates of absorption of infrared radiation.

History

The French mathematician Jean Fourier observed how the atmosphere absorbed and reflected radiation, and coined the term "greenhouse effect" in 1822. Prior to the Industrial Revolution of the 1700s, climate change was purely a natural phenomenon. Technological changes in industry and agriculture during that time period meant that, for the first time, human activities began to alter the planet's climate and increase its overall temperature.

Human activity continues to increase the amount of greenhouse gases in the atmosphere, primarily through burning fossil fuels (coal, oil, natural gas) for electricity, home heating and cooling, transportation, and industry; burning solid wastes; cutting down rainforests; industrial farming; and manufacturing cement.

The U.S. government publishes an annual national greenhouse gas inventory that tracks emissions since 1990, in order to meet obligations to the U.N. Framework Convention on Climate Change, an international agreement dating to 1994 that laid the groundwork for the Kyoto Protocol. The United States currently produces more greenhouse gases than any other country, although China and India are quickly catching up and will likely to surpass the U.S. in the near future (on a national basis, if not per capita). China in particular has been increasing its energy production capacity to serve a fast-growing population, mostly by burning coal-one of the dirtiest forms of energy production.

The ability of the United States to reduce its greenhouse gas emissions remains hampered mostly by politics and economics, rather than science, with one camp advocating a flat cap on emissions versus those who promote a cap-and-trade program, in which those who emit less greenhouse gases could sell their rights to those who wish to emit more, as long as an overall level was maintained.

Context

In one sense, the science of greenhouse gases is without controversy; these gases are, in fact, necessary for human survival. Without them, the average temperature of the Earth's surface would be slightly less than 0 degrees Fahrenheit. With the greenhouse effect, the average surface temperature is a more livable 59 degrees.

Unfortunately, the science of global warming is also without controversy: more greenhouse gases in the atmosphere leads to a warmer planet, and we are now at the point where the growing concentration of these gases is raising the planet's average temperature each year-with consequences that grow increasingly dire, from more droughts and floods to severe weather of many kinds.

What so-called global warming skeptics have for years attacked-in ever-smaller numbers as scientific evidence repeatedly disproves their case-is the idea that the growing amounts of greenhouse gases in the atmosphere are caused by humans. This is a fact accepted by the overwhelming majority of scientists and other experts. Levels of carbon dioxide are higher now than they have been at any time in more than 650,000 years, and they continue to rise. This has a disruptive effect on climate, weather, and ecosystems around the globe.

Human emissions of greenhouse gas can be reduced by several methods, from the use and development of cleaner energy technologies to the changing of everyday personal habits. Simple changes that would decrease one's personal greenhouse gas emissions include conserving energy at home, recycling, buying a more fuel efficient car, and carpooling or using mass transit. tists and other experts. Levels of carbon dioxide are higher now than they have been at any time in more than 650,000 years, and they continue to rise. This has a disruptive effect on climate, weather, and ecosystems around the globe.

Human emissions of greenhouse gas can be reduced by several methods, from the use and development of cleaner energy technologies to the changing of everyday personal habits. Simple changes that would decrease one's personal greenhouse gas emissions include conserving energy at home, recycling, buying a more fuel efficient car, and carpooling or using mass transit.