This article appears in the autumn edition of Natural Fibres Insight.
It’s no great secret that for years, wool has carried a heavy burden in environmental assessments. Life cycle assessments (LCAs), the standard tools used to measure environmental impact, have often painted wool as one of fashion’s most climate-intensive fibres. At the heart of this issue is methane, the greenhouse gas emitted by sheep during digestion.
On paper, the figures around sheep and methane look damning. But new research led by Dr James Blignaut and Dr Paul Swan, presented at the IWTO Congress in Lille this summer, argues that this story has been told with a calculator missing half the buttons.
Think of this issue like measuring the finances of a household by counting only the money going out, not the money coming in. That is, in essence, how wool has been judged historically.
LCAs rooted in older ISO standards (14040 and 14044) have focused almost entirely on emissions. They do not take into account that wool is produced in what scientists call a “biogenic system.” This is a living cycle in which carbon is not just emitted but constantly absorbed, transformed, and stored in soils and plants.
A closed-loop cycle
The researchers call their method a “biogenic life cycle approach.” Put simply, they looked at wool farming not as a straight line of emissions but as a loop. Carbon enters the system when sheep graze on grasses that have absorbed CO₂ from the atmosphere. That carbon then flows through the animals and the farm system, with much of it returning to the soil or back to the atmosphere in forms that are reabsorbed by plants.
Imagine a revolving door in a hotel lobby. People (carbon molecules) are constantly coming in and out, but the number inside at any one moment is balanced. What older LCAs did was count everyone leaving the hotel as a loss, ignoring those re-entering through the revolving door. This new approach puts the whole picture in much clearer focus.
To test their approach, the researchers re-analysed six major wool-producing systems in Australia, originally documented by Wiedemann et al. in 2016. Their model followed every gram of carbon consumed by sheep. Here is what they found:
– About 54 per cent of the carbon is excreted as manure.
– Around 23 per cent is released through respiration.
– About 7.5 per cent is in urine.
– Only 5 per cent appears as methane and nitrous oxide, the gases that LCAs have focused on.
– Roughly 10 per cent is embedded in products ie wool, meat, milk.
From a material balance perspective, the system is largely circular. The same carbon cycles around, with only a small fraction turning into long-lived greenhouse gases.
So why do current LCAs give wool such a high carbon score? Because those small fractions are multiplied by global warming potential factors from the IPCC, which inflate them relative to their absolute contribution.
The role of soils: nature’s bank account
The real game-changer comes when soils are brought into the equation. Soil can act like a bank account for carbon. When manure breaks down, some of its carbon is locked into the soil, where it can remain for years or decades. How much is retained depends on soil health, grazing practices, and climate.
The study explored how much of the carbon in sheep manure is absorbed by the soil and how this affects wool’s carbon footprint. When a third of the manure carbon was retained in the soil (33 per cent retention), the carbon footprint of wool dropped by around half or even more (compared with conventional, emissions-only life cycle assessments), depending on the farm system. At two-thirds retention (66 per cent), the carbon footprint of wool was close to neutral. In several cases, the system actually became net negative, meaning that the farm stored more carbon in soils and vegetation than it released through emissions.
Studies cited by the authors show that under the right conditions, soils can retain up to 90 per cent of manure carbon. In other words, the bank can be very efficient at saving deposits, though its performance varies by farm.
Beyond wool
These findings go beyond wool. They strike at the heart of how we measure the environmental impact of biological systems. If we fail to count biogenic cycles, we risk mislabeling natural fibres as worse than synthetics, even though synthetics are made from fossil carbon that has been locked underground for millions of years and cannot cycle back into the biosphere.
The result is a systemic bias, where tools like the Higg MSI rank wool as more damaging than polyester, driving brands towards fossil-based fibres.
As the authors warn, this is not just a technical glitch but a systemic misfit. By ignoring biogenesis, LCAs inflate the emissions of natural fibres and undermine investment in regenerative agriculture. They risk pushing the industry in precisely the wrong direction at a time when policy and consumer expectations demand lower-impact materials.
Metaphors for a living system
The researchers often use imagery to explain their case. Wool production, they say, is more like a forest than a factory. Carbon flows through it, nourishing life, and then returns to the system, ready to be used again. Unlike oil wells or coal mines, which release ancient carbon with no return cycle, sheep grazing systems are part of nature’s circulation.
It is the difference between drinking from a flowing spring and emptying a one-off bottle of water. One replenishes itself; the other, once gone, is gone forever.
To find out more about the paper’s findings we caught up with Dr Paul Swan for Natural Fibres Insight.
Swan argued passionately that the shift from ISO 14040 to ISO 14067 is overdue. “ISO14040 and 44 have been around for decades, and they shaped the way carbon accountants think. But they never even mention the words ‘fossil’ or ‘biogenic’,” he explained. For him, this has allowed industries built on fossil carbon to hide behind accounting rules that treat all carbon as the same.
“There’s technical inertia,” he said, “and then there’s commercial interest. Fast fashion benefits from the way LCAs are currently structured, because ignoring the difference between fossil carbon and biogenic carbon makes biodegradable materials look worse than they are.”
The soil question
One of the most striking parts of the research was the assumption of soil carbon retention. Critics might say these figures are optimistic. Swan admitted that manure retention rates vary widely, from as little as 10 per cent to as high as 90 per cent, depending on soils and grazing practices. “Sadly, manure retention has not been a focus of environmental verification schemes. But we hope our work changes that. Greater recognition of biogenic flows will drive more attention to soil management.”
Some observers also might worry that acknowledging biogenic cycles might let livestock industries off the hook. Swan is blunt in his response. “The risk of undue leniency is minimal compared with the danger of relying on eco-accounting systems that misrepresent biological realities. Those systems are convenient for fossil-fibre industries and for fast fashion, but they don’t reflect the truth.”
What about the challenge of fitting biogenic recognition into international accounting frameworks still tied to IPCC methods? Swan sees a way forward. He says: “ISO 14040 and 44 already say that system boundaries should match the goal of the study. The problem is that practitioners treat biogenesis as optional. We need to change that. Regulators should require tools like Higg or Ecobalyse to account for biogenic flows, including biodegradability and even the impact of microplastic pollution from synthetics.”
Beyond wool?
Is this model unique to wool? Swan does not think so. “Conceptually, it could apply to any product of living systems – cotton, hemp, alpaca, meat. Wool is not unique in its carbon cycle, though it does have functional benefits like reusability, flame resistance, odour resistance, and even the ability of wool carpets to absorb indoor pollutants.”
Onto the million-dollar question. Namely, if soil carbon is to be counted, how can it be verified across millions of hectares? Swan acknowledged the challenge but pointed to technology. “Soil carbon can be measured, but it is costly. The good news is that with new modelling tools and low-cost monitoring such as satellite sensing, there will be many opportunities for brands and certifiers to develop scalable verification systems.”
The research relied heavily on reanalysing existing data. But Swan emphasised that more real-world studies are coming. “Case studies are now being carried out in South Africa, Australia, New Zealand and the UK. The first major commercial case study is already complete and will form the basis of our next publication.”
These studies will test the model against farm-level data and build confidence among sceptics.
What this body of work shows is that wool’s carbon story is not as simple as emissions-only LCAs suggest. By ignoring the revolving door of biogenic carbon, current methods continue to write wool off unwittingly, and unscientifically. Bringing soils and cycles into the picture changes everything. What once looked like a debit may in fact be a balance, or even a credit.
For brands, policymakers and consumers, the overriding message is that not all carbon is created equal. Fossil carbon is a one-way street. Biogenic carbon is a loop. And wool, as part of that loop, deserves to be measured on its own terms.
Dr Swan puts it: “In nature, one life nourishes the next. Carbon, the skeleton of life, flows from form to form. Nothing is wasted.”
