In my last post on carbon offsets, we looked at various aspects of "space shifting", or the practice of emitting CO2 in one location and offsetting in another. In that I asked whether this really worked in practice, and I got some excellent comments and emails that indicate that it does.
I got a number of people suggesting that CO2 mixed pretty quickly, but the most direct was from Marcus Sarofim at MIT, the CO2 in the earth's atmosphere mixes every 1 to 2 months within a hemisphere, and 1 to 2 years between hemispheres. This is far less than the time the CO2 is in the atmosphere, and also far less than the 70 years of productive CO2 sequestration from our trees, so it sounds like this is not a concern! (Marcus cites this report, and notes that this is not true for other green house gasses, so space shifting may not be as viable for those).
So it looks like space shifting is OK for CO2!
Another thing I questioned in that post was the ability for trees planted in the northern hemisphere to be good sequester-ers of CO2. Marcus and others argued that the potential issue is an albedo effect where the dark trees absorb more heat than the open space they replaced. However, this report from the EPA indicates that there are a number of factors at work, and that the amount is limited by how much you want to spend managing the planted trees. In particular, at $5 per ton of CO2, the capacity for CO2 sequestration due to new forests in the US is very limited.
The next post we'll take a look at whether sequestration projects such as Dell's can scale....