Biogenic Carbon and Wool: Why Not All Emissions Are Equal

When we talk about the environmental impact of yarn, we often hear carbon talked about as though all forms of it are exactly the same.

We might read that a certain yarn (or any product) has a specific carbon footprint, or that one fibre produces a certain number of kilograms of carbon emissions while another produces less. This makes it tempting to simply label one as better and the other as worse.

However, carbon accounting can hide a very important detail: where the carbon came from in the first place.

That distinction matters immensely when we compare wool with synthetic fibres such as acrylic.

The Short Carbon Cycle: Wool, Grass and Sheep

Sheep eat plants.

Those plants have recently taken carbon dioxide from the atmosphere through photosynthesis. The sheep digest the plants and, being ruminant animals, emit methane as part of their digestive process.

That methane enters the atmosphere. Methane is powerful while it is there, but it is relatively short-lived compared with carbon dioxide. After roughly a decade or so, it breaks down into carbon dioxide and water. That carbon dioxide can then be taken up by plants again.

In simple terms, the very same carbon is cycling through a continuous biological loop: from the air, into the grass, into the sheep, into the air as methane, and back into the grass again.

This is called the biogenic carbon cycle.

It does not mean the emissions do not matter. They absolutely do. Methane warms the planet while it is in the atmosphere. But it does mean that the carbon in livestock methane is part of a shorter biological loop. It came from the atmosphere recently, was captured by plants, eaten by animals, emitted and can return to plant growth again.

Sheep on pasture in rural Ceredigion. Wool’s emissions are part of a biogenic carbon cycle, which differs from releasing long-stored fossil carbon.

The Long Carbon Cycle: Fossil Fuels and Acrylic

Now compare that with fossil fuels.

Acrylic yarn is made from petrochemicals. Those petrochemicals come from fossil carbon, which is carbon that was locked safely underground for millions of years.

When fossil fuels are extracted and used, that ancient stored carbon is brought into the active atmosphere. It is not simply cycling through grass and animals. It is entirely new carbon being added to the modern climate system.

That is a fundamentally different pathway.

Carbon dioxide from fossil fuels can remain in the atmosphere and climate system for centuries. It takes roughly a thousand years for the earth to reabsorb it into geological storage. It is not part of a quick seasonal or biological loop in the same way as biogenic carbon.

Biogenic carbon moves in a short loop. Fossil carbon brings long-stored carbon into the atmosphere.

Why This Matters for Wool

This distinction is one reason wool can look worse than it really is in simple comparisons.

Many carbon footprint calculations use a measure called carbon dioxide equivalent. This converts different greenhouse gases into a single number so they can be compared. That can be useful, but it can also be misleading if it treats short-lived biogenic methane and long-lived fossil carbon too similarly.

The climate impact of wool is often dominated by methane from sheep. The impact of acrylic is tied to fossil fuel extraction and petrochemical production. Those are not the same kind of carbon story.

This does not give wool a free pass, because sheep methane still contributes to warming. But it does mean that comparing wool and acrylic using only one headline carbon number can miss something crucial.

Stable Flocks, Growing Flocks and Warming

There is another subtle but vital point.

If livestock numbers are stable over time, then the amount of methane being emitted may roughly replace the methane that is simultaneously breaking down. In that situation, the flock may not be adding much new warming, although it is still maintaining an existing level of warming.

If livestock numbers increase, methane emissions increase too. That clearly adds new warming.

So the size and trend of the global flock matters. A stable, well-managed flock is different from an expanding system producing more and more methane.

What This Means for Knitters

For us as knitters and crocheters, the takeaway is not that wool has no impact.

The takeaway is more thoughtful than that. Wool emissions are real, but much of the climate impact comes from biogenic methane. Biogenic methane is part of a much shorter carbon cycle than fossil carbon. Meanwhile, acrylic is tied entirely to fossil carbon and petrochemical production.

Simple carbon footprint comparisons do not always tell the full story. That is exactly why we need to look beyond one number.

In the next post, we will use this understanding to compare wool and acrylic properly. We will look beyond the carbon footprint and examine microplastics, lifespan, biodegradability and what happens at the end of life.