Climate Passport Carbon Offsets Available at SF International Airport
San Francisco International (SFO) is committed to being green. They have efforts underway to reduce their environmental impact by reducing noise, reducing global warming and preserving natural resources like air and water.
" ... recognize the importance that environmental sustainability plays in helping achieve this goal ... committed to drastically reducing its environmental impact over the next decade. ... working to reduce contributions to global warming, improve air and water quality, reduce noise impacts, and preserve natural resources." 
SFO n
ow offers the Climate Passport program; a way to help travelers reduce their travel carbon footprint by purchasing offsets.
Here is how it works ... " ... drop by a kiosk that will calculate the carbon impact of your travel ... buy offsets from the kiosk manager, 3Degrees, ... Some of the money will also go to the San Francisco Carbon Fund ... offsets purchased ... are verified by the Climate Action Registry."
Check out the interactive carbon calculator ...
On Sunday Oct 18, the cost for a carbon offset for a round trip flight from Philadelphia to San Francisco and back would cost $22.82 and off set 3,727 lbs of CO2.