Where do carbon offsets come from? How do I know these offsets are legitimate?

1 year of flying 1 year of driving (hybrid) 1 year of driving (avg) 1 year of home energy
(4 short and 2 long flights) (12000 miles) (12000 miles) (average sized house)
$13 $37 $60 $112
3 mos. of flying 3 mos. of driving (hybrid) 3 mos. of driving (avg) 3 mos. of home energy
(1/4 of the full year offset) (1/4 of full year offset) (1/4 of full year offset) (1/4 of full year offset)
$3.6 $11 $22 $48
The personal footprint package is based on your carbon footprint (calculate it now!)
1 year personal footprint 1 year family footprint Offset gift certificate
(your personal footprint) (average family of 4) (buy a custom sized offset)
$? $163
calculate footprint

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