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Grazing animals have an unexpected role in climate change

A new study from Massachusetts Institute of Technology reveals that there’s a fine line between grazing that benefits our planet and grazing that contributes to climate change.

When you think of climate change, images of smokestacks and cars likely come to mind. But did you know that the way we manage the land where livestock graze plays a major role in either storing or releasing harmful greenhouse gases?

Sustainable grazing

Grazing, when done responsibly, plays a crucial role in the ecological balance of grassland ecosystems. This age-old practice, involving livestock like cattle, sheep, and goats feeding on grass, has a more profound impact on the environment than meets the eye.

As these animals graze, they consume plant material, which might seem like a straightforward process. However, this act of grazing does more than just feed the livestock. It triggers a chain of ecological events that can lead to healthier, more vibrant grasslands.

When animals graze on plants, they often eat the older, tougher plant parts, which can stimulate the plants to grow back healthier and more vigorous. This regrowth is not just beneficial for the animals in terms of providing more food; it also plays a crucial part in the cycle of plant life and soil enrichment.

Grazing and climate change

The stimulation of new plant growth is key to one of the most critical ecological services grazing provides: carbon sequestration. Plants absorb carbon dioxide (CO2) from the atmosphere during photosynthesis, using the carbon to grow new leaves, stems, and roots, and releasing oxygen back into the air.

When animals graze on these plants, a portion of the carbon is transferred into the soil through the plants’ root systems, which are enhanced by the grazing activity.

Moreover, as part of their natural digestive process, grazing animals also contribute organic matter back to the soil through their manure. This manure acts as a natural fertilizer, rich in nutrients and organic carbon, further enhancing soil health and its ability to store carbon.

This cycle of growth, grazing, and manure deposition increases the soil’s organic matter content and its capacity for carbon sequestration.

Tipping point of grazing

The MIT study discovered an alarming fact: there’s a tipping point. When grazing becomes too intense, the benefits quickly reverse. Excessive grazing strips the land, leading to soil erosion and the release of vast amounts of stored carbon.

“When you cross a threshold in grazing intensity, or the amount of animals grazing there, that is when you start to see sort of a tipping point—a strong decrease in the amount of carbon in the soil,” explained Cesar Terrer, the study’s lead researcher.

Grazing in different climates

Grazing’s impact on carbon storage depends heavily on factors like temperature, rainfall, and soil type. This means the same grazing approach can have wildly different results in different places. In warmer climates, microbes in the soil work faster, potentially breaking down stored carbon and releasing it into the atmosphere.

Cooler temperatures slow this process, allowing more carbon to stay in the ground. Similarly, grasslands with plenty of rain support healthier, more productive plants that pull in more carbon from the air. This can lead to more carbon stored in the soil long-term.

Arid areas can’t support the same level of growth, limiting the potential for carbon storage. Finally, the soil itself matters. Clay-rich soils hold carbon better than sandy ones, and factors like soil chemistry are important.

Hence, it’s essential to consider local conditions when talking about grazing and climate change. Trying to use a “one-size-fits-all” approach or relying solely on general guidelines won’t accurately reflect what’s happening on the ground.

Impact of grazing on climate change

To understand the global scale of this issue, the researchers analyzed a massive amount of data from grazing lands around the world.

The results were sobering: 46 petagrams (that’s 46 billion metric tons!) of carbon have been lost from the soil due to grazing in recent decades. To put this in perspective, that’s more than four years’ worth of global fossil fuel emissions.

Yet, there’s also a glimmer of hope: the study revealed that if we change our grazing practices, we could recapture 63 petagrams of carbon. For context, that’s roughly equal to 30 years of carbon accumulation from the natural regrowth of forests worldwide.

Carbon capture

While the potential to make our grasslands into powerful carbon-fighting tools is huge, the path to restoring them isn’t easy. To achieve optimal levels of carbon capture, the study suggests the world needs to decrease grazing intensity in roughly 75% of current grazing areas.

This could mean major changes in how we raise livestock. It might require shifting to more plant-based diets to reduce the number of grazing animals or drastically changing how we manage herds by moving them more frequently to avoid overgrazing.

Study significance

“This is a rigorous and careful analysis that provides our best look to date at soil carbon changes due to livestock grazing practiced worldwide,” said Ben Bond-Lamberty, an independent expert in the field who was not involved in the study.

The team isn’t stopping here. They’re already asking the next big question: what’s the overall climate impact of changing the way we eat?

Could a shift towards more vegetarian meals, alongside better grazing management, be a powerful part of the climate change solution?

The study is published in the journal Nature Climate Change.

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