How Sustainable Is Your Holiday Lamb?

Lamb is a traditional symbol of springtime, and that’s one of the most popular times to eat it: Americans consume about a pound per person each year, and 20 percent of that happens around Easter, Passover and other springtime holidays. Lamb’s popularity among immigrant communities and as a halal meat helps keep demand high during the rest of the year. Whenever you shop for it, you might have noticed that most of the lamb in the grocery store is stamped with an Australia or New Zealand country of origin label. Over half the lamb eaten in the US is imported, but why? And what does this mean for sustainability?

The Carbon Footprint of Lamb

Intuitively, a local product should have a lower carbon footprint than an imported one because it doesn’t have to travel as far. But the reality is a little more complicated. There are a lot of factors that determine a carbon footprint, and food miles are only part of the equation. When it comes to animals like sheep and cows, what they eat, where they live and how they’re raised makes a big difference. Cow burps have gotten a lot of attention as a major source of greenhouse gasses, but sheep are ruminants too, and they have the same complicated digestive system that uses bacteria to help break down tough plants. This allows them to digest grass, but it also means they produce methane, which is a more powerful greenhouse gas than carbon dioxide. Other stages of raising sheep, like growing feed, irrigating and fertilizing pastures and running equipment also contribute to the overall carbon footprint of lamb.

Diet can change the carbon footprint of lamb: A 2013 study of 60 lamb farms in the UK found grain-finished lamb had a significantly higher carbon footprint than lamb that was entirely pastured. More recent research from California found less clear results: farms that finished lambs on grain had slightly lower carbon footprints than those that didn’t. In both cases, the grain-grass divide was less important than other factors like altitude and the breed of sheep. 

Most of the emissions in lamb production come from the sheep burping methane, a finding backed by other work from New Zealand. This was true even when researchers included the entire refrigeration and shipping chain to get lamb to the UK from New Zealand, suggesting food miles are less important than how lambs are raised. Overall, studies of the carbon footprint of lamb suggest that it’s very similar to beef, with about 10 to 20 kilograms of carbon dioxide produced per kilogram of finished lamb. 

Do Carbon Footprints Overlook the Benefits of Grazing?

Significantly, none of the studies examined whether or not raising sheep on pasture put more carbon into soil, which is a major benefit of raising animals on pasture. Soil can store a lot of carbon, which accumulates as plant roots and manure decomposes. Most grain farming disturbs soil and causes this carbon to disappear. Carefully managed grazing, on the other hand, has the potential to add carbon to the soil; grass roots stay in place, and animals are constantly adding fresh fertilizer in the form of manure. Studies from beef production have shown that taking soil carbon into account can radically change the footprint of meat, even making it carbon negative. 

Soil carbon can be hard to measure, so it hasn’t been included in many studies of sheep. Still, some data from Europe suggests that well-managed sheep grazing can increase soil carbon in alpine pastures. The authors of the California study also pointed out that even if carbon benefits are unclear, there are a number of other benefits to grazing sheep. They can naturally manage weeds and efficiently turn waste — like the stubble of harvested crops in a field — into food.