Human Activity And Greenhouse Gases
The world’s economy runs on carbon: the “fuel” in fossil fuels. Coal, oil, and natural gas contribute energy to nearly every human endeavor in industrialized nations, and carbon dioxide (CO2) is a by-product of burning these fuels. Immediately eliminating CO2 emissions would literally stop the industrial world. This graph illustrates how thoroughly fossil fuels and CO2 emissions are integrated into American life.
 |
U.S. Greenhouse Gas Emissions by Sector, 1997
In 1997, different sectors of the U.S. economy emitted millions of metric tons of carbon dioxide. Industry was the largest contributor, producing 610 million metric tons. Transportation emitted 470 million metric tons, residential 300 million metric tons, and commercial 280 million metric tons. Agriculture was also a contributor, with 120 million metric tons of carbon dioxide emitted. |
CO2 contributes more to the recent increase in greenhouse warming than any other gas. CO2 persists in the atmosphere longer and longer as concentrations continue to rise.
Other chemicals such as methane, nitrous oxide, and halocarbons also contribute to the global greenhouse effect. A number of additional chemicals related to urban pollution, such as low-level (tropospheric) ozone and black soot, can have a strong regional and perhaps global warming effect. Sulfate aerosols may have a cooling effect.
 |
Contributions of Atmospheric Gases and Solar Radiation to Warming
Scientists have estimated the contribution to warming made by a range of gases, dust and solar radiation. They have a high level of certainty that greenhouse gases contribute the most to warming, with increases in CO2 as the greatest contributor with about 1.4 watts/meter2 and methane, nitrous oxide, and halocarbons making smaller contributions. Scientists have a lower level of certainty about the contributions of reductions in stratospheric ozone and increases in tropospheric aerosols, which cool the Earth by 0.3 watts/meter2 and 0.9 watts/meter2 respectively. Solar radiation may also contribute to warming but scientists have a very low certainty about the level of this contribution.
|
| 
