Division of Energy

Global Climate Change: The Greenhouse Effect

The greenhouse effect as applied to the Earth's atmosphere derives its name from an analogy with the effect of the glass in a greenhouse, which allows the sun's rays to enter, but prevents the heat from escaping. This trapped heat cannot mix with the cooler outside air.

Most of the sun's light (about 70 percent) reaches the earth, while the earth's atmosphere reflects about 30 percent of the sun's rays back into space. When solar radiation strikes the earth's surface, part of it is re-radiated into the atmosphere. In the earth's atmosphere, the greenhouse effect due to water vapor and other trace gases in the atmosphere such as carbon dioxide (CO2), chlorofluorocarbons (CFCs), methane (CH4), and nitrous oxide (N2O) is a well established phenomenon. These gases allow incoming solar radiation to reach the earth but block outgoing infrared radiation. This results in a warming of the atmosphere. Consequently, these infrared-absorbing gases are sometimes called greenhouse gases.

The green-house effect was recognized by scientists as early as 1822. French mathematician Jean Fourier observed that the atmosphere reflected the earth's radiation back to the surface.

The greenhouse gases trap the Earth's radiated energy, which warms the surface of the earth by about 60 degrees Fahrenheit. Without the greenhouse effect, the Earth's average temperature would be -3 degrees Fahrenheit, which is uninhabitable for man. Indeed, it is doubtful whether any life at all would have evolved.

The primary greenhouse gas is water vapor. On a global scale, the evaporation and precipitation of water is a process that cannot be controlled by human activities. Because of this, the discussion of greenhouse gases has centered around the gases which man contributes to the atmosphere. Altering human behavior can have a more significant impact on these gases.

Ozone, CFCs and the Greenhouse Effect

Ozone (O3) close to the earth's surface is harmful to human health. It causes respiratory problems. Older people and babies are most susceptible to these types of problems.

Ozone is produced in the upper levels of the atmosphere (the stratosphere) where it serves a beneficial purpose to the earth. It shields the earth from the sun's harmful ultraviolet radiation. This radiation causes skin cancer, cataracts on the eyes, and has other detrimental affects on humans, plant, and animals. Migration of CFCs to the stratosphere has resulted in a layer of stratospheric ozone.

Stratospheric ozone also is a greenhouse gas. Because CFCs are both greenhouse gases and destroyers of ozone, CFCs produce a cooling effect by means of ozone depletion. Therefore, the net contribution of CFCs to the greenhouse effect is uncertain. In fact, the cooling effect of ozone loss may be large enough to have offset a significant part of the heating from increases in all greenhouse gases over the past decade. If the warming effect of CFCs is offset by the newly discovered cooling effect, then the phasing out of CFC use will not decrease global warming.

Sources of Greenhouse Gases in Missouri

The primary sources of greenhouse gases in Missouri are carbon dioxide from the use of fossil fuels and methane from agricultural activities and solid waste landfills. Methane emissions are inherently difficult to control. Carbon dioxide is not only the most important greenhouse gas but it is the easiest to control.

The most important sources of CO2 in Missouri are transportation, industrial, residential and commercial activities. Energy consumption in the transportation and commercial sectors has grown steadily since 1960. In contrast, energy use in Missouri's industrial sector peaked in the 1970s, and residential use has shown no clear growth pattern.

In 1992, the transportation accounted for 33 percent of energy use in Missouri. The commercial sector's share was 19 percent. The remaining 48 percent of energy consumption were split evenly between the industrial and residential sectors.

The most significant reduction in greenhouse gas emissions can come from fossil fuel use. Energy conservation measures often can provide other economic and environmental benefits while reducing greenhouse gas emissions.

Conclusion

The greenhouse effect is a naturally occurring phenomenon that has made it possible for plant and animal life to develop on earth. Man's release of large quantities of greenhouse gases into the atmosphere could increase the greenhouse effect and speed global warming or cause other large-scale climatic changes. While the projections of global warming or other climate changes are uncertain, the potential consequences are so severe that we should look for ways to reduce the level of greenhouse gases released into the atmosphere.