Is All CO2 Equal? Part 4 - Space Shifting

Following the last part in this series where we looked at times shifting of CO2 offsets (offsetting the CO2 at a different time that it was emitted), in this post we'll look at space shifting, or offsetting the CO2 at a different place than it was emitted.

Dell's program involves planting trees in order to sequester the CO2 due to PC usage. The CO2 emissions will occur at a power plant somewhere near where you're using the PC (although with today's power grids it may not be all that close). Dell's program is in partnership with the Conservation Fund who plants trees throughout the US. Through their overall program they've planted around 5.5M acres (not all of this is for offsetting purposes, though it still helps), 3M in the west, 1M in New England, and the rest in the southeast, midwest and Rocky Mountain region.

At this surface this looks pretty reasonable - sequestration is spread across the same area where emissions are occurring. However, we notice that 60% or so of the emissions are in the west, and only 20% of the US population is there. So this raises an obvious question: can the western US sequester CO2 emitted in the east, midwest and south? Or, more generally, if can we space-shift CO2 offsets? Or (I can't resist) if a tree grows in the forest and there's no emitters around, does it sequester?

I've spent the last couple of weeks looking into this question, and I've come up empty. If someone has done real science on this, please let me know, but I can't even find anyone asking the question.

This question is important to ask. There are reports that trees planted outside of the tropics may not be a net reduction of CO2. There's a bunch of CO2 offset projects which reduce CO2 in developing nations and sell the offsets in developed ones. So in an extreme case, you can ask yourself this: would carbon offsets work if all of the offset projects were in South America and Africa, and all of the credits were sold in North America, Europe and Asia?