Standard LCA methodology has overstated wool's greenhouse gas emissions intensity for over a decade by excluding biogenic carbon from the calculation. A review applying a more complete accounting framework to six Australian wool enterprises found that emissions intensity dropped dramatically under all modelled scenarios, and that wool production could reach carbon neutrality—or better—when realistic rates of manure carbon retention in soil were applied.
- Prior LCA studies of wool production, covering 102 individual observations across six countries, recorded an average emissions intensity of 24.1 kg CO₂eq/kg greasy wool, with individual values ranging from 1.1 to 61.4 kg CO₂eq/kg.
- When biogenic carbon flows were incorporated, average emissions fell substantially even under worst-case conditions, with no manure retention assumed.
- At a lower-bound realistic manure retention rate, average emissions dropped to less than a third of the conventional LCA baseline, varying by enterprise.
- The findings are drawn from 'When LCAs include the sheep, wool can be carbon neutral', published earlier this month in Agricultural Systems.
BEHIND THE RESEARCH: This paper is the first application of ISO 14067:2018 to wool production, extending a landmark Australian wool LCA dataset to map the full biogenic carbon economy of six representative Australian wool enterprises. The study reviewed 14 peer-reviewed LCA studies published between 2010 and 2024 and modelled outcomes across three major agroecological zones in Australia.
- The NSW High Rainfall Zone covered temperate, superfine Merino production near Armidale, representing high-rainfall pastoral conditions.
- The WA Wheat-Sheep Zone involved mixed cropping and grazing operations under winter-dominant rainfall in Western Australia.
- The SA Southern Pastoral Zone covered semi-arid, large-framed Merino production near Hawker in South Australia.
- The model was validated against Wiedemann et al. (2016), returning a Pearson Correlation Coefficient of +0.92 across six paired case studies and an average difference of just −0.5% when identical global warming potential factors were applied.
- The study was authored by James Blignaut (ASSET Research; Stellenbosch University; South African Environmental Observation Network), Paul Swan (Paul G. Swan and Associates Pty. Ltd., Sydney) and Lemuel Blignaut (Stellenbosch University).
WHERE THE CARBON GOES: Across the six case studies, sheep ingested an estimated 3,829 tonnes of carbon per year in dry matter. That carbon was distributed across nine biological pathways, revealing that enteric and manure-based gaseous emissions—the figure most commonly cited in conventional LCAs—accounted for only 5.2% of all carbon consumed, while the dominant pathway was excretion as manure at more than half of total ingested carbon.
- Manure accounted for 54.1% of all ingested carbon, making it by far the largest single carbon pathway across the six enterprises studied.
- Respiration represented 22.7% of ingested carbon, released as the net difference between carbon inhaled and exhaled by the animals.
- Urine accounted for 7.5%, milk production for 3.8%, and live sheep sales for 3.5% of total ingested carbon leaving the farm system.
- Wool itself physically stored 1.9% of ingested carbon in the fibre at shearing, with mortalities retaining 0.9% on-farm and lambs at birth embodying 0.4%.
- Enteric and manure-based gaseous emissions varied between 4.3% and 7.5% across individual case studies, averaging 5.2%—far below what standard emissions modelling has historically assumed.
THE MANURE FACTOR: Because manure accounts for the largest share of carbon throughput, its fate on farm proved decisive in determining wool's net carbon balance. Retention rates in published literature range from 10% to over 90%, depending on climate, soil health, and grazing management. The authors modelled three scenarios spanning this range, with results that fundamentally altered wool's emissions profile.
- Under the emissions-only baseline, with no biogenic carbon accounted for, average emissions intensity was 22.5 kg CO₂eq/kg greasy wool, broadly consistent with prior LCA literature.
- At 0% manure retention, where all manure carbon volatilises, average emissions fell to 13.7 kg CO₂eq/kg greasy wool—a reduction of around 39% from the emissions-only baseline.
- At 33.3% manure retention, the lower-bound realistic estimate, average emissions dropped to 6.6 kg CO₂eq/kg greasy wool, a reduction of between 57% and 77% depending on the enterprise.
- At 66.7% manure retention, the upper-bound realistic estimate, the average reached −0.4 kg CO₂eq/kg greasy wool, a reduction of between 75% and 115%, meaning wool production shifted from a net source to a net carbon sink.
- Under the GWP metric, which more accurately captures the warming impact of stable short-lived climate gases such as methane, the emissions-only baseline averaged 8.8 kg CO₂eq/kg greasy wool, falling to −14.2 kg CO₂eq/kg greasy wool at 66.7% manure retention.
A WIDER FLAW: The methodological bias introduced by ISO 14040 and ISO 14044 extended well beyond wool. Designed as general-purpose frameworks without biogenic carbon guidance, their application to living biological systems produced systematically skewed results—overstating natural fibre emissions and understating their sustainability relative to fossil-based alternatives. ISO 14067, published in 2018, was the first standard to explicitly recognise biogenic carbon and provide a framework for its quantification and reporting.
- The Higg Materials Sustainability Index, which did not account for biogenic carbon, ranked natural fibres including wool as responsible for the highest environmental damage, while fossil-based fibres such as polyester, nylon and acrylic scored among the lowest.
- Norwegian and Dutch regulators challenged the Higg MSI methodology in 2022, raising concerns about its validity as a basis for sustainability comparisons between natural and synthetic fibres.
- For bio-energy systems, the effect of accounting for biogenic carbon ranged from +86% to −50% depending on scenario, further illustrating the scale of distortion in conventional LCA outputs.
- Farmers investing in rotational grazing, cover crops and soil biota management may become net carbon removers, yet such outcomes would go entirely unrecognised under conventional LCA methodology.
- The biogenic carbon content physically stored in wool fibre at farm gate was approximately 1.71–1.74 kg CO₂eq/kg greasy wool, representing carbon removed from the atmosphere through photosynthesis.
