I tried to get an answer for you from my colleague. More fodder. Here it is:
I was thinking was along the lines that offsets like Terrapass should be used as a second choice for travel and other emissions that cant be reduced any other way which, in many cases, is flying for work; personal transportation to and from the office is often more malleable.
Theres still some scattered debate about the value of offsets, mostly having to do with the fact that were emitting that carbon NOW, and it would only be reduced in the FUTURE via offsets, and how exactly it will translate to carbon savings.
As an example of some of this uncertainty, some offset companies plant trees to absorb carbon but the latest science says that doing so in temperate climates may actually increase warming due to the fact that darker green foliage can absorb more sunlight than lighter-colored grasslands (it is, however, a benefit in tropical areas). On the other hand, trees are still way cooler than parking lots, and have other benefits as well
My take is that offsets are better than not doing anything, but that thinking we can entirely buy our way out of this problem may not be as successful as figuring out how to reduce its cause in the first place, both in our individual lives and in terms of how utilities produce energy.
Just as an example of how weve worked this out at home: we did buy offsets for our houses emissions and my husbands travel to work, since he works too far from home to bus or bike (although he drives our Prius). However, I didnt feel justified in just buying offsets to cover me driving to work, since its an easy bus or bike ride. It cost around $200 for the year through www.carbonfund.org
. It would have cost a whole lot more if we added in my work-related flights.
Heres a Q and A about how it works: http://www.grist.org/comments/intera...on/index1.html
Also, the best guide I know of as to the pros and cons of different offset programs is: