As major exponents of greenhouse gases that warm the Earth, what cows consume is increasingly gaining attention from scientists trying to apply the brakes to global methane emissions. The latest promising discovery in this area comes from an international team of researchers, who have found that livestock plant food grown in warmer climates leads to higher methane releases, and could potentially be inhibiting milk and meat production at the same time.

Methane emitted by cows, or from any source for that matter, is a problem because it is 25 times more potent than carbon dioxide as a greenhouse gas, due to its superior heat-trapping abilities. Meanwhile, global meat production is on the rise, from 71 million tons in 1961 to 318 million tons in 2014.

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So scientists have been looking at the effects of livestock diets, and how they might be tweaked to reduce the amount of methane produced by the world's growing bovine population. Last year, Australian scientists identified a strain of seaweed that can reduce methane emissions by 99 percent, while earlier this year another research team discovered that feeding cows tropical leaves in addition to regular food could cause also cause sharp decline.

The latest research doesn't unearth new dietary supplements, rather it reveals an already existing culprit. Scientists from Royal Botanic Gardens, Kew, Scotland's Rural College, and the Senckenberg Biodiversity and Climate Research Centre in Frankfurt studied published data on forage quality, and found that nutritional value of grass was reduced at higher temperatures.

This is turn makes it harder for grazing livestock to digest the plants, and the scientists say there are a few reasons that might be. The extra heat causes plants to adapt and they may flower earlier, produce thicker leaves or possibly allow tougher invasive plants to spread into new areas and replace more nutritious species. With the plants tougher to digest, they spend longer inside the animal and produce more gas, and the scientists say this is setting in motion a vicious cycle.

"The vicious cycle we are seeing now is that ruminant livestock such as cattle produce methane which warms our planet," says Dr. Mark Lee, a research fellow at Royal Botanic Gardens, Kew. "This warmer environment alters plants so they are tougher to digest, and so each mouthful spends more time in the animals' stomach, producing more methane, further warming the planet, and the cycle continues. We need to make changes to livestock diets to make them more environmentally sustainable."

With an eye to the future, the scientists used published empirical models to estimate how changes to the climate will impact global methane production. They found that methane production increased by 0.9 percent with a 1 °C temperature rise (1.8 °F), and by 4.5 percent with a 5 °C rise (9 °F). They expect this to be a worldwide trend, but did identify hotspots in North America, Central/Eastern Europe and Asia, places where livestock farming is increasing and climate change is expected to hit hardest.

"Now is the time to act, because the demand for meat-rich diets is increasing around the world," says Lee. "Our research has shown that cultivating more nutritious plants may help us to combat the challenges of warmer temperatures."

The research paper was published in the journal Biogeosciences.

Source: Royal Botanic Gardens, Kew