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ISO/TR 25080 — Wood and Wood-Based Products: Background and Examples of Calculating Contributions to Carbon Stored in Harvested Wood Products (HWP)
Comprehensive Guidance for HWP Carbon Accounting Using IPCC-Aligned Tier 1, Tier 2, and Tier 3 Methodologies
1. Introduction to Harvested Wood Product Carbon Accounting
ISO/TR 25080:2025, prepared by ISO/TC 287 (Sustainable processes for wood and wood-based products), provides background information, methods, and examples for calculating contributions to carbon stored in harvested wood products (HWP). The document supports the implementation of ISO 13391-1 by explaining the HWP coefficient concept and its application across multiple tiers of methodological sophistication, from simple Tier 1 approaches to more data-intensive Tier 3 calculations.
Wood-based products in use extend the time of biogenic carbon storage until the material is disposed of, after which the carbon is released to the atmosphere, enters landfills, or meets a different fate. The pool of carbon in HWPs has an inflow of new woody material and an outflow of disposed material. The difference between inflow and outflow in a given period represents the net change in the HWP pool — this net change is what matters for greenhouse gas accounting.
The HWP coefficient represents the proportion of the current year’s inflow that represents a net addition to the HWP pool. A coefficient of 0.5 means that 50% of the carbon in products placed on the market this year will remain stored after accounting for outflows from past years’ products reaching end-of-life.
2. HWP Coefficient Calculation Methodologies
ISO/TR 25080 explains three tiers of methodological complexity for calculating HWP coefficients, aligned with IPCC guidelines.
| Tier | Data Requirements | Key Parameters | Applicability |
|---|---|---|---|
| Tier 1 | Product quantities by category; default half-lives from IPCC | Half-life (e.g., 2 years for paper, 30 years for sawnwood, 50 years for wood panels) | Organizations with limited data; first approximations |
| Tier 2 | Country-specific half-lives; market growth/decline data | Refined half-life values; historical production data | National reporting; organizations with market data |
| Tier 3 | Organization-specific residence time modelling; detailed end-of-life fate data | Custom decay functions; recycling rates; landfill degradation rates | Advanced LCA; product-level carbon footprinting |
2.1 First Order Decay Model
The core modelling approach uses a first-order decay function, where the HWP coefficient (c) is calculated as: c = 1 – (1 – d) / (k + d), where k is derived from the half-life (k = ln(2) / half-life) and d represents the market growth rate. A stable market (d = 0) with a 30-year half-life yields a coefficient of approximately 0.5. A growing market produces a higher coefficient, while a declining market produces a lower coefficient — potentially even negative, though ISO 13391-1 sets a floor of zero in such cases.
A declining market for wood products can result in a negative HWP coefficient, meaning the HWP pool is shrinking and carbon is being released. However, assigning a negative storage effect to an organization that is currently delivering carbon-storing products is problematic. ISO 13391-1 addresses this by allowing the coefficient to be assumed as zero in this case.
3. Engineering Design Insights: Practical Considerations
ISO/TR 25080 provides detailed guidance on several practical aspects of HWP carbon accounting:
3.1 Recycling and Cascading Use
Recycling extends carbon storage and complicates the accounting. When a product is recycled, the carbon moves to a new product pool with potentially different half-life characteristics. The document recommends accounting for recycling by adjusting the effective half-life or by tracking material through multiple use cycles. The Tier 1 coefficients provided in the document include default recycling factors for key product categories.
3.2 Landfill Carbon Storage
A significant portion of HWP carbon ends up in landfills, where anaerobic conditions can preserve wood for extended periods. The IPCC guidelines recognize that carbon in landfills decays slowly, with half-lives on the order of decades. ISO/TR 25080 provides Tier 1 approaches for estimating landfill carbon storage contributions based on disposal rates and degradation factors, as well as Tier 2 methods that consider landfill type (standard vs. non-standard) and methane capture efficiency.
3.3 Sensitivity Analysis
The worked examples in Clause 9 demonstrate how HWP coefficients are sensitive to assumptions about half-life, market growth rate, and recycling rate. A change in half-life from 25 to 35 years can change the coefficient by 10-15%. Engineers should perform sensitivity analyses to understand the range of plausible outcomes and communicate this uncertainty in their reporting.
For organizations in the forest products sector seeking to quantify their carbon footprint and contribution to climate change mitigation, the HWP coefficient methodology described in ISO/TR 25080 offers a scientifically robust approach that is consistent with IPCC guidelines and can be implemented at a level of complexity appropriate to the organization’s data availability and reporting objectives.
4. Frequently Asked Questions
Q1: How does ISO/TR 25080 relate to national greenhouse gas inventory reporting?
The document aligns with the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Organizations can use the methods described to contribute to national reporting or for voluntary corporate carbon accounting.
The document aligns with the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Organizations can use the methods described to contribute to national reporting or for voluntary corporate carbon accounting.
Q2: What product categories are covered by the HWP coefficients?
The document provides coefficients for sawnwood, wood-based panels, paper and paperboard, and other wood products. Recycling factors are included for products that incorporate recycled content.
The document provides coefficients for sawnwood, wood-based panels, paper and paperboard, and other wood products. Recycling factors are included for products that incorporate recycled content.
Q3: Can HWP coefficients be used for carbon offset claims?
HWP coefficients quantify carbon storage in products, which is distinct from carbon offsets. Organizations should consult relevant carbon accounting standards (e.g., ISO 14064, GHG Protocol) for guidance on offset claims.
HWP coefficients quantify carbon storage in products, which is distinct from carbon offsets. Organizations should consult relevant carbon accounting standards (e.g., ISO 14064, GHG Protocol) for guidance on offset claims.
Q4: How often should HWP coefficients be recalculated?
Coefficients should be recalculated periodically as market conditions and product mix evolve. A review every 3-5 years is generally appropriate, or whenever significant changes occur in production patterns or end-of-life management.
Coefficients should be recalculated periodically as market conditions and product mix evolve. A review every 3-5 years is generally appropriate, or whenever significant changes occur in production patterns or end-of-life management.
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