Tuesday, August 12, 2008

The Rules for Carbon Accounting of Harvested Forests

This is a techie post, but it is important that we all understand how this works to understand the real emissions that are the result of paper production, consumption and disposal.

The Intergovernmental Panel on Climate Change sets the rules by which countries report their Greenhouse Gas Emissions. The IPCC is empowered to make these rules according to the United Nations Framework Convention on Climate Change. Nearly every country, including the United States, is a signatory.

With all that in mind, let’s focus on the rules around emissions from harvesting forests and the storage of carbon in forest products. The rules for measuring carbon stored in ecosystems is actually pretty straightforward: the balance of carbon stored there year after year is measured (estimated) based on estimates for which the IPCC provides methodologies. Change in the carbon stored are reported either as an emission (the amount of carbon went down) or a removal (the amount of carbon went up). It is called a removal because the ecosystem removes carbon from the atmosphere. At present, the U.S. is estimated to be carbon positive, as trees grow more than they are cut down or are otherwise lost. This is the equation given in the IPCC’s Good Practice Guidance for Land-Use, Land-Use Change and Forestry for national greenhouse gas reporting of the carbon balance in forests:

The equation means that the change in forest carbon is equal to the change in living biomass plus the change in dead organic matter plus the change in soils.

There are also rules for accounting for harvests of forest products. This is the most significant issue with regard to the paper industry, since it lays out the rules by which the most important input into the industry is accounted for in terms of carbon emissions. Let’s focus on the Good Practice Guidance equation 3.2.7 “Annual Carbon Loss Due to Commercial Fellings.” The loss due to logging (a.k.a. harvest) is calculated as:

[losses from commercial fellings] = [the volume of wood extracted] x [wood density] x [biomass extraction factor] x [carbon left to decay] x [carbon content of the wood harvested]

For our purposes, we need to understand that the wood harvested is an emission of carbon and we also need to include the wood that is left in the forest that will decay and that must be accounted for as well. Thus, when accounting for inputs into products or the use of biomass for energy, harvested wood must be counted as an emission. There really is no ambiguity around this fact.

Those who state ‘biomass is carbon neutral’ (a normative statement, not a scientific one) rely on statements like this one in the 1996 Revised Guidelines for national greenhouse gas reporting:

“Biomass fuels are included in the national energy and CO2 emissions accounts for information only. Within the energy module biomass consumption is assumed to equal its regrowth.”
You see, they say, emissions are reported “for information only” and “biomass consumption is assumed equal to regrowth!” What they don’t say is why, as the very next sentence makes clear:

“Any departures from this hypothesis are counted within the Land Use Change and Forestry module.”
The reason biomass is not reported as an emission in the energy section of the reporting is because it would be double-counting to do so, as this emission has been accounted for already under forests. This view is accepted by the good people at the EPA and at Environment Canada who compile the numbers for the national greenhouse gas reports for the two countries. EPA said:

The net change in forest C is not equivalent to the net flux between forests and the atmosphere because timber harvests do not cause an immediate flux of C to the atmosphere. Instead, harvesting transfers C to a “product pool.” Once in a product pool, the C is emitted over time as CO2 when the wood product combusts or decays. The rate of emission varies considerably among different product pools. For example, if timber is harvested to produce energy, combustion releases C immediately. Conversely, if timber is harvested and used as lumber in a house, it may be many decades or even centuries before the lumber decays and C is released to the atmosphere. (emphasis added)
The Canadian National Report on Greenhouse Gas Emissions states the following:

In keeping with the current IPCC (2003) default methodology, emissions from forest management activities comprise all the CO2-C contained in harvested roundwood and harvest residues. All carbon transferred out of managed forests as
wood products is deemed an immediate emission.

Let’s proceed to a simplified example of how this might work:

In one year, a country could have 100 units of carbon in forests. If that country lets that carbon grow (as trees will do if left alone), then perhaps the next year the balance could be 105 units. In this scenario, the country gains five units of carbon that can be applied to its greenhouse gas emissions and is equal to an offset of other emissions. If that same country instead harvests the forests for ten units of carbon, counts these emissions, and also counts its growth of five units, ending up with a balance of 95 units. That is, most of the forests grew and it would have gone to 105, but ten units were removed and thus the country’s balance is 95, causing an net emission of five to be added to the country’s total emissions. For this harvest we would also need to calculate the carbon that was left in the forest to decay, and there are rules around how to do that. This ranges from 7% in boreal ecosystems to 25% in tropical plantations.

Thus, within the forest calculation, the harvest is an emission and all harvests must be treated as such. The system presumes forests will grow. Indeed trees grow whether we cut them or not. There are many complexities to how fast they grow at different stages of ecosystem re-growth (e.g., very young trees accumulate little carbon as do very old forests, while intermediate-aged trees are perhaps the most robust accumulators of carbon). There are also complexities about ownership, the intent of owners or managers, additional growth from management practices, etc. However, these rules in methodology allow us to make a simple estimate of the emissions from wood harvest to use in Carbon Footprinting or carbon accounting.

In a later post I will discuss how the portion of biomass removed from forests can be sequestered in products and specifically in paper as the IPCC rules allow, as well as an estimate done by the US Forest Service Forest Products Lab.


I was remiss in not posting the actual equation for accounting the "Annual Carbon Loss from Commercial Fellings," which is equation 3.2.7 in the IPCC Good Practice Guidance, Chapter 3. Here is the equation and notes about what the notation means taken directly from the guidance:


Shannon said...

Great explanation and vital as well. Thanks for posting this.

Mary Serreze said...

Thanks for this post. I have been curious about the source of the oft-reported statement that woody biomass incineration is "carbon-neutral."