Senin, 08 Juni 2009


Solar radiation heats the earth. The average temperature at the earth’s surface is approximately 287◦ K, and typically varies from 220◦ Kto 320◦ K [Sørenson, 2000, page 26]. Daily variations in temperature are due to the rotation of the earth around its axis. Seasonal variations in temperature are due to the rotation of the earth around the sun and the angle of inclination of the earth’s axis relative to the ecliptic plane.

Measurements of ambient air temperature show a global warming effect that corresponds to an increase in the average temperature of the earth’s atmosphere. The increase in atmospheric temperature can be traced to the beginning of the twentieth century [Lide, 2002, page 14–32] and is associated with the combustion of fossil fuels. When a carbon-based fuel burns, carbon can react with oxygen and nitrogen in the atmosphere to produce carbon dioxide, carbon monoxide, and nitrogen oxides (often abbreviated as NOx). The combustion byproducts, including water vapor, are emitted into the atmosphere in gaseous form. Some of the gaseous by-products are called greenhouse gases because they capture the energy in sunlight that is reflected by the earth’s surface and reradiate the energy in the form of infrared radiation. Greenhouse gases include carbon dioxide, methane, and nitrous oxide, as well as other gases such as volatile organic compounds and hydrofluorocarbons.

Global warming due to the absorption of reflected sunlight and subsequent emission of infrared radiation is called the greenhouse effect because greenhouse walls allow sunlight to enter the greenhouse and then trap reradiated infrared radiation. Some of the incident solar radiation from the sun is absorbed by the earth, some is eflected into space, and some is captured by chemicals in the atmosphere and reradiated as infrared radiation (heat). The reradiated energy would have escaped the earth as reflected sunlight if greenhouse gases were not present in the atmosphere.

Carbon dioxide (CO2) is approximately 83% of the greenhouse gases emitted by the United States as a percent of tonnes of carbon or carbon equivalent. Wigley, Richels and Edmonds [1996] projected ambient CO2 concentration through the twenty-first century. Preindustrial atmospheric CO2 concentration was on the order of 288 parts per million. Atmospheric CO2 concentration is currently at 340 parts per million. The concentration of CO2 that would establish an acceptable energy balance is considered to be 550 parts per million. To achieve the acceptable concentration of CO2 through the next century, society would have to reduce the volume of greenhouse gases entering the atmosphere.

The Kyoto Protocol is an international treaty that was negotiated in Kyoto, Japan in 1997 to establish limits on the amount of greenhouse gases a country can emit into the atmosphere. The Kyoto Protocol has not been accepted worldwide. Some countries believe the greenhouse gas emission limits are too low, and would adversely affect national and world economies without solving the problem of global warming. Research is underway to develop the technology needed to capture and store greenhouse gases in geologic formations as an economically viable means of mitigating the increase in greenhouse gas concentration in the atmosphere. The storage of greenhouse gases in an environmentally acceptable manner is called sequestration.

Reff : Fanchi-Energy, Technology and Direction for the Future

Tidak ada komentar:

Posting Komentar