“When you factor in the fertilizer needed to grow animal feed and the sheer volume of methane expelled by cows, a carnivore driving a Prius can contribute more to global warming than a vegan in a Hummer.”
—Christina Agapakis, synthetic biologist at UCLA

For those of us keen to keep our carbon footprints to a minimum, we tend to think about reducing carbon dioxide by addressing how we burn fossil fuels. We look to renewable sources of energy, minimize electricity use, and sometimes even purchase carbon offsets to cover the carbon dioxide we can’t avoid generating in our 21st century lifestyles.

But of course, carbon dioxide isn’t the only greenhouse gas. Methane and nitrous oxide play a role too. In fact, methane is about twenty times more potent as a greenhouse gas than carbon dioxide is, and nitrous oxide is more than 300 times as potent. Fortunately, they are in such smaller concentrations—for example, methane is around 1,750 parts per billion compared with carbon dioxide’s 394 parts per million—so carbon dioxide still plays a bigger part in global warming, according to most experts. At least for now.

A huge source of both methane and nitrous oxide is the meat industry. The number of cattle on the planet is about 1.3 billion, more than one head of cattle for every five people on Earth. So it would make sense that if we had less cattle and other ruminants like sheep on the planet, we would generate less methane.

So eating less meat will make a difference. In my book “Comprehending the Climate Crisis,” I addressed this issue and advocated that readers consider “Meatless Mondays” as part of their dietary regimen. Since every little bit helps, moving toward a vegetarian diet will have an impact. Going vegan will help even more, since vegetarian still means animal products are being consumed, so the animals are still out there generating emissions.

This isn’t just tree-hugging rhetoric. A 2010 report from the United Nations stated that a shift towards a vegan diet was one of the best ways we could tackle climate change. According to senior U.N. Food and Agriculture Organization official Henning Steinfeld, the meat industry is “one of the most significant contributors to today’s most serious environmental problems.”

It’s more complicated than simply trying to minimize cows belching out methane, it turns out. Raising animals for food is an involved process. They require massive amounts of grain and water, and once they’re slaughtered for meat there’s processing, transporting, and storage. All of these steps take energy, all of which generate carbon dioxide emissions in the process.

There are other emissions associated as well: the destruction of trees—thus losing their photosynthesis contributions—occurs to provide pastures and crops for these animals; animal manure releases carbon dioxide because of bacterial activity. All told, producing one calorie from animal protein requires as much as eleven times the energy input as it takes to produce one calorie of plant protein.

To support the quote at the beinning of this post, a study from the University of Chicago published in 2007 demonstrated that switching a regular car for a Toyota Prius saves about one ton of carbon dioxide emissions. Being vegan, however, saves about 1.5 tons. Additionally, a German study from 2008 showed that meat-eaters generate about seven times the emissions as vegans do. Rajendra Pachauri, head of the U.N.’s Nobel Prize–winning Intergovernmental Panel on Climate Change (IPCC) makes this request of the public: “please eat less meat—meat is a very carbon-intensive commodity.” (Pachauri is a vegetarian, so he’s walking the wallk himself.)

As nice as it is to encourage people to make such behaviour changes in the name of saving the planet, in the decades to come such decisions may be forced on us. The Stockholm International Water Institute (SIWI) is reporting that our planet will be facing a major food crisis before too much longer. The global population is predicted to exceed nine billion by 2050 and livestock require disproportionately higher amounts of water. Given these two facts, it’s not surprising that a report from SIWI is stating that continuing to generate animal protein at present levels of about 20 percent of our diet is simply not sustainable.

The report was released as part of the World Water Conference (WWC) in Stockholm, Sweden this past week. The WWC is an annual meeting involving over 2,500 politicians, UN bodies, NGOs and researchers from 120 countries, all working to address global water concerns.

The recommendation is that our species needs to cut consumption of animal protein down to about five percent instead of twenty precent in order to avoid the catastrophe of a mojor food shortage for the world’s people. And as global warming threatens to affect crops and our sources of fresh water, “crisis” may not be a strong enough word to describe what we’ll be facing.

I think the point is clear: reducing consumption of animal products will help the problem. For myself, I’ve cut down my meat to about once a week. As a physician, I’ve always felt strongly that some things like vitamin B12 come best from animal products, so I’m not ready to go vegan myself. But I’ve also recognized that a lot of us eat much more meat than we should, with adverse effects to our cardiovascular health as a result.

An interesting point: last year my youngest son decided to become vegetarian at the age of nine, not for any of the reasons listed above, but simply because of how much he loves animals. As a result, our family has been gradually adopting a diet reduced in meat anyway, simply by following his lead. Turns out it’s not as hard as you might think.

So next time you’re making dinner or eating at a restaurant, think twice about how much your meal’s emissions are contributing to the problem you already care so much about.