As self-appointed eco watch dog for scientific accuracy, I can't help commenting on Adam Stein's "Science corner: why carbon sequestration and clean energy are equivalent" on the TerraPass site.
I agree that sequestering a ton of CO2 and avoiding emitting a ton of CO2 can be viewed as scientifically equivalent, assuming that both activities happen within the same period of time. However, Adam ignores this time stipulation, and unfortunately the common practice in forest-based sequestration is to ignore it as well.
Here's the issue. Many tree-based carbon sequestration programs use the money to plant a tree, which will then sequester the targeted CO2 over a period of years. However, that period may be a long time, such as the 70 year period targeted by Dell's Plant a Tree program. That means that 35 years from now, only half of the CO2 will be sequestered.
If someone argues that we can wait a few decades to do something about CO2 emissions, alot of us, including, presumably Adam, would have a fit. However, the forest-based sequestration crowd follow Adam's argument and are somehow comfortable with sequestration which has 2/3 of its effect over 20 years from now.
What we really need is a net present value (NPV) of CO2, just like we have with money. A dollar in the future isn't worth as much as a dollar in hand today, so a discount rate is applied to the future dollar to give you a current value. Similarly, a ton of CO2 30 or 40 years from now isn't as value as a ton of CO2 today. In fact, I could argue that its worth a lot less, if in fact we are faced with a 10 to 20 year horizon to really make a real dent in our atmospheric CO2.
Unfortunately, since we have no NPV for carbon, and the idea of it isn't widely understood, people are putting programs into place that pretend that the value of a future ton is worth a ton today. And when defenders of sequestration-based offsets apply flawed reasoning, and worse yet call it 'scientific', it only lessens my already weak faith in the offset system as an element of a functional and effective carbon market.
Note: I've ignored another potential issues with Adam's argument. He is assuming that investments and circumstances cooperate in order to keep sequestered CO2 sequestered. Our ability to do this at massive scale still seems a little dicey to me.