The treatment of long-lived, carbon-containing products in inventories of carbon dioxide emissions to the atmosphere

The United Nations Framework Convention on Climate Change (UNFCCC) requires that all parties to the convention periodically report their emissions of greenhouse gases and the Intergovernmental Panel on Climate Change (IPCC) has published guidelines on how to estimate these emissions. Estimating carbon dioxide (CO 2) emissions is complicated by the fact that consumption of fossil-fuels and harvesting of forests do not necessarily mean that the contained C has been released to the atmosphere as CO 2. Some fractions of fossil-fuels and harvested wood are incorporated into products that have lifetimes ranging from months to centuries. The IPCC methodology addresses durable products by assuming that some prescribed fraction goes to permanent storage while the remainder is oxidized instantly. The question posed here is whether the annual increase in stocks of durable products, i.e. the difference between the rates of production and oxidation, can be reasonably estimated as a simple fraction of their current rate of production. Although the annual stock change can be described as a simple fraction of annual production when production is growing exponentially and oxidation is a first order decay process, a description of annual stock changes needs to consider how both production and oxidation are evolving with time, regardless of the functional forms of these changes with time.