OK, I'm going to come right out and admit it: carbon accounting and offsets hurt my brain. There's too many parts that feel like apples to oranges, and I keep thinking myself into corners.
Before we get into my personal issues, let me describe what I'm talking about. Carbon dioxide (CO2) is one of the most prevalent green house gasses. As it is a common byproduct of extracting energy from fossil fuels (oil, natural gas, coal), most of our everyday activities generate CO2 as a direct or indirect effect. For example, in the US producing electricity creates, on average, around 1.3 lbs of CO2 per kWH. So a 60W bulb running for 16 hours (about 1 kWH), produces 1.3 lbs of CO2 that generally goes into the atmosphere.
Now if I want to reduce my CO2 production, I can do it a number of ways. First, I could stop doing whatever it is that's producing CO2. Second, I can find greener sources of energy for what I want to do, maybe use a hybrid car or install some solar cells for electricity. Finally, I can do what I was going to do, but purchase some CO2 credits or "offsets" which counterbalance my creation of CO2. (if you want some history on this type of trading system, check out Wikipedia's article on emissions trading).
Offsets derive from a couple of sources. First, the money you pay may be used to fund alternative energy sources. Second, it may fund the development of carbon sequestration sources, or, in english, things that will take green house gasses out of the atmosphere. Planting trees is a popular form of sequestration. Finally, organizations can get credit for CO2-reducing activities that are beyond "business as usual". This last set are the most controversial and difficult to understand.
The critical question is what does it mean to counterbalance or offset my CO2 production? This is a topic of hot debate. A number of organizations have put themselves in a position of "blessing" CO2 offsets (example), but of course, since there's more than one of those, there isn't agreement among them and they don't necessarily make things clearer. To get an idea of the depth and complexity of this discussion, you might take a look at this report from Clean Air/CoolPlanet, the rebutals (1, 2) from Terrapass, a popular group which helps individuals with personal CO2 offsets, and an analysis of it on Gristmill aptly titled "Ranking carbon offset provi... hey, where you going?".
One last note. People often get sloppy between talking about CO2 and carbon. You'll often hear people talk about "carbon offsets", when they really mean CO2 offsets. Sometimes things are measured in carbon, so there is a conversion required to switch between CO2 and carbon mass measurements. For example, in this useful site you'll see that a carbon calculation is multiplied by 44/12 to get the amount of CO2. That's because the carbon atom has an approximate molar mass of 12, vs. the two oxygen atoms at 16 each. So the total is 44, 12 of which is carbon.
Whew. So that's some background. Given the complexity of this topic, I've decided to break it into an as-yet undetermined number of parts. In the next few parts we'll look at a specific example, and in the last parts I'll summarize and discuss some of the internal debate and thought processes that are going on within Sun on this topic.