Below the Surface is not affiliated with Carbonfund.org, but is curious about the Carbon Economy and has chosen this site as an example of the principle.
How many tons of CO2 did that weekend vacation from San Diego to San Jose, CA just generate? Between 0.18-2.4 kg/passenger mile according to one carbon offset site call Carbonfund.org. So a 2-passenger round trip flight from San Diego to San Jose, CA emits between 0.32 and 0.86 tons of CO2, which can be offset for between $3.19-8.61 according to Carbonfund.org. This donation to offset your usage goes to conservation projects on this site: http://www.carbonfund.org/projects
What is Radiative Forcing?
At high altitudes, the effect of greenhouse gases is considerably different than on the ground level. Aircraft also emit water vapor during flight which can cause the formation of ice clouds, called contrails. Where contrails persist, cirrus clouds begin to form which have an additional impact on global warming. Clouds can have a double effect on radiation: they warm the earth by reducing the amount of radiation from the earth that escapes into space but also cool the earth by reflecting the sun’s rays back into space. However, contrails lead to a net warming factor, which is estimated to be 2.7 times the normal effect (IPCC, 1999).
Carbonfund.org's Carbon Calculators use information from the US Department of Energy's Energy Information Agency and other sources to develop an accurate assessment of carbon dioxide emissions emitted per energy type or use. (By the way, the EIA maintains an excellent website with easy-to-understand and easy-to-access figures about all things energy related. We recommend you check it out at: www.eia.doe.gov.)