Carbon stocks of particle board and fiberboard in Japan.

The carbon stock function of harvested wood products (HWPs) is attracting attention among climate change countermeasures. Among HWPs, particle board (PB) and fiberboard (FB) mainly use recycled materials. This study estimated carbon stocks of PB and FB and their annual changes over the past 70 years in Japan using three methods of the Intergovernmental Panel on Climate Change guidelines: Tiers 1-3. Tier 1 uses first order decay (FOD), a 25-year half-life, and the Food and Agriculture Organization of the United Nations database. Tier 2 uses FOD, a 25-year half-life, and Japan-specific statistics. Tier 3 uses a log-normal distribution for the decay function and a 38-63-year half-life of building PB/FB. Japan's PB and FB carbon stocks have increased for the past 70 years. The latest carbon stock in early 2022 and the annual change in carbon stock in 2021 was 21.83 million t-C and 0.42 million t-C/year, respectively for Tier 3. Tier 3 has the highest estimation accuracy by using decay functions and half-lives that match the actual conditions of building PB and FB, whereas Tiers 1 and 2 were underestimates. Approximately 40% of the carbon stock is derived from waste wood, which extends its utilization.

Estimation of carbon stocks in wood products for private building companies.

Wood products function as carbon storage even after being harvested from forests. This has garnered attention in relevance to climate change countermeasures. In the progress of efforts toward climate change mitigation by private companies, the effective use of wood products has been an important measure. However, the methodology for accounting carbon stocks in wood products for private companies has not been established. Therefore, this study investigated methods for estimating carbon stocks in wood products used in wooden houses built by private enterprises, targeting a major company in the Japanese building industry. The results indicated that both the direct inventory method and flux data method (FDM) were applicable for estimating the carbon stocks. These two methods use data that can be obtained from many other building companies, thus, indicating high versatility. The log-normal, Weibull, normal, and logistic distributions, in descending order, proved to be suitable lifetime functions of wooden houses under the FDM, with a half-life of 66-101 years. It is important to continuously acquire time-series data on the floor areas of both newly built and existing houses and the amount of wood products used to improve the accuracy of estimates and explore future predictions.

The default methods in the 2019 Refinement drastically reduce estimates of global carbon sinks of harvested wood products.

BACKGROUND: The stock dynamics of harvested wood products (HWPs) are a relevant component of anthropogenic carbon cycles. Generally, HWP stock increases are treated as carbon removals from the atmosphere, while stock decreases are considered emissions. Among the different approaches suggested by the Intergovernmental Panel on Climate Change (IPCC) for accounting HWPs in national greenhouse gas inventories, the production approach has been established as the common approach under the Kyoto Protocol and Paris Agreement. However, the 24th session of the Conference of the Parties to the United Nations Framework Convention on Climate Change decided that alternative approaches can also be used. The IPCC has published guidelines for estimating HWP carbon stocks and default parameters for the various approaches in the 2006 Guidelines, 2013 Guidance, and 2019 Refinement. Although there are significant differences among the default methods in the three IPCC guidelines, no studies have systematically quantified or compared the results from the different guidelines on a global scale. This study quantifies the HWP stock dynamics and corresponding carbon removals/emissions under each approach based on the default methods presented in each guideline for 235 individual countries/regions. RESULTS: We identified relatively good consistency in carbon stocks/removals between the stock-change and the atmospheric flow approaches at a global level. Under both approaches, the methodological and parameter updates in the 2019 Refinement (e.g., considered HWPs, starting year for carbon stocks, and conversion factors) resulted in one-third reduction in carbon removals compared to the 2006 Guidelines. The production approach leads to a systematic underestimation of global carbon stocks and removals because it confines accounting to products derived from domestic harvests and uses the share of domestic feedstock for accounting. The 2013 Guidance and the 2019 Refinement reduce the estimated global carbon removals under the production approach by 15% and 45% (2018), respectively, compared to the 2006 Guidelines. CONCLUSIONS: Gradual refinements in the IPCC default methods have a considerably higher impact on global estimates of HWP carbon stocks and removals than the differences in accounting approaches. The methodological improvements in the 2019 Refinement halve the global HWP carbon removals estimated in the former version, the 2006 Guidelines.

Climate change mitigation effect of harvested wood products in regions of Japan.

BACKGROUND: Harvested wood products (HWPs) mitigate climate change through carbon storage, material substitution, and energy substitution. We construct a model to assess the overall climate change mitigation effect (comprising the carbon storage, material substitution, and energy substitution effects) resulting from HWPs in regions of Japan. The model allows for projections to 2050 based on future scenarios relating to the domestic forestry industry, HWP use, and energy use. RESULTS: Using the production approach, a nationwide maximum figure of 2.9 MtC year-1 for the HWP carbon storage effect is determined for 2030. The maximum nationwide material substitution effect is 2.9 MtC year-1 in 2050. For the energy substitution effect, a nationwide maximum projection of 4.3 MtC year-1 in 2050 is established, with at least 50 % of this figure derived from east and west Japan, where a large volume of logging residue is generated. For the overall climate change mitigation effect, a nationwide maximum projection of 8.4 MtC year-1 in 2050 is established, equivalent to 2.4 % of Japan's current carbon dioxide emissions. CONCLUSIONS: When domestic roundwood production and HWP usage is promoted, an overall climate change mitigation effect is consistently expected to be attributable to HWPs until 2050. A significant factor in obtaining the material substitution effect will be substituting non-wooden buildings with wooden ones. The policy of promoting the use of logging residue will have a significant impact on the energy substitution effect. An important future study is an integrated investigation of the climate change mitigation effect for both HWPs and forests.