more about trees...

Thanks to Chuck, for posting a question about the February 25 entry. His question was: "Do tree-based carbon offsets work off of predicted future growth, or actual real time growth?"

To investigate this question, I turned, of course, to the world wide web. After a good surfing session, the only thing I can come up with is that methods for calculating offsets can vary from company to company. Terrapass, a popular seller of other types of carbon offsets, suggests that the most common way that companies market carbon offsets from reforestation is by advertising sequestration rates of 40 year old trees. There is an obvious problem with this ploy, given the fact that saplings and young trees don't sequester nearly as much carbon as a 40 year old tree. This is just one of the reasons cited by Terrapass for not using this method of carbon sequestration. Other reasons they list are: sales of offsets for reforestation make the hefty assumption that the forest will be permanent, and that the trees won't die or burn, also it is difficult to measure the amount of carbon offset by tree planting, thirdly leakage can occur (see 2/25 post), fourth there is some evidence that forests decrease the earth's albedo (reflectivity) enhancing global warming, fifth monoculture has its own host of issues, and the list goes on. Of course, Terrapass's website may be biased since they don't actually offer this sort of offset, but the opinions and ideas expressed are echoed all over the scientific community.

Whereas selling carbon offsets for tree planting is relatively laissez-faire in the market at large, there are more stringent rules if you wish to register your offsets in some official context. One example is the Wisconsin Emission Reduction Registry, a service of the Wisconsin Department of Natural Resources. The DNR website offers an explanation of and access to a spreadsheet that anyone can use to calculate the offsets produced by planting a given number of a variety of different types of trees. They also outline a set of rules that must be adhered to if one wants to register voluntary offsets in the state of Wisconsin. These comprehensive guidelines require the budding offsetter to determine the baseline (I'm assuming this means starting conditions of carbon flux on the land to be reforested), quantify their offsets using the aforementioned spreadsheet, verify their offsets, and keep close records of the activity.

By including calculations for tree classification, tree age, growth rate and survival rate, users of the DNR's spreadsheet can determine total carbon sequestered over time as well as individual year carbon sequestration amounts. The Wisconsin Emission Reduction Registry does not allow for aggregation of carbon sequestered over a number of years, however, if emissions can be accurately calculated, then the carbon sequestered by a given tree in a given year can be considered an offset for that year. For instance, the carbon sequestered in 2008 by 4-year-old tree counts for equivalent offsets in the year 2008, but you can't also consider the tree's total life-time carbon sequestration. At least, that's how I understand it.

At any rate, to the best of my knowledge, there is not a universally mandated procedure for calculating the carbon offsets for planting trees, unless you wish to register your offset with a group like the Wisconsin Emission Reduction Registry. Until there are stricter regulations, I don't view this method as either very reliable or effective. It is wonderful to plant trees, and there are a host of positive environmental contributions associated with restoring native forests to deforested lands. I am suspicious of this activity, however, in terms of its efficacy in offsetting the CO2 spewing out of my tailpipe.