February 20, 2015 3:24PM

Diet Change and Climate Change

A draft set of new dietary guidelines released yesterday by the U. S. Department of Health and Human Services (HHS) and the Department of Agriculture (USDA) was backed by a 571-page scientific report from the 2015 Dietary Guideline Advisory Committee (DGAC) that was assembled by the Obama administration.

The Washington Post reports that, for the first time ever, the Dietary Guidelines took into consideration the environmental impacts of food production in recommending that Americans decrease their consumption of red meat and increase their intake of plant-based food.

This is from the DGAC’s Executive Summary (emphasis added):

The major findings regarding sustainable diets were that a diet higher in plant-based foods, such as vegetables, fruits, whole grains, legumes, nuts, and seeds, and lower in calories and animal based foods is more health promoting and is associated with less environmental impact than is the current U.S. diet. This pattern of eating can be achieved through a variety of dietary patterns, including the Healthy U.S.-style Pattern, the Healthy Mediterranean-style Pattern, and the Healthy Vegetarian Pattern. All of these dietary patterns are aligned with lower environmental impacts and provide options that can be adopted by the U.S. population. Current evidence shows that the average U.S. diet has a larger environmental impact in terms of increased greenhouse gas emissions, land use, water use, and energy use, compared to the above dietary patterns. This is because the current U.S. population intake of animal-based foods is higher and plant-based foods are lower, than proposed in these three dietary patterns. Of note is that no food groups need to be eliminated completely to improve sustainability outcomes over the current status.

Among the environmental considerations is greenhouse gas emissions, which are significant for one reason only: climate change (despite the DGAC report explicitly stating it did not take into account climate change).

This is another example of the breadth of Obama’s Climate Action Plan—although one not announced as such … yet.

In anticipation, I wanted to see just what kind of a climate change impact these dietary guidelines could potentially avert.

My calculations are admittedly rough, but you’ll see once you get to the end, that it hardly makes much of difference even if I am off my an order of magnitude.

I’ll work through the extreme case that all Americans switch to becoming vegetarians (not a current recommendation of the DGAC).

According to a 2013 report from the United Nations Food and Agriculture Organization (FAO), globally, in 2005, greenhouse gas emissions from livestock production produced 7,100 million metric tons of carbon dioxide equivalents (mmtCO2-eq). Of that amount, 45% came from feed production, 39% from enteric fermentation, 10% from manure handling, and the remainder from bringing the product to market.

Of the global total, North American livestock production was responsible for just under 10%, or about 650 mmtCO2-eq.

Another study out last year compared the carbon footprint for different types of diets. It found that diets high in meat consumption had about twice the carbon footprint of vegetarian diets.

Combining the results of those studies (and assuming Canadian production amounts of about 10% of the North American total), I find that if all Americans become vegetarians, it would reduce greenhouse gas emissions by about 300 mmtCO2 per year.

So now, all that is left is to determine the climatic impact of 300 mmtCO2 (a calculation that the Obama administration strongly advises against). In previous work, I detailed a quick and dirty way to do this (see here for details). The result is that it takes about 1,767,250 mmtCO2 to raise the average global surface temperature by 1°C. (Note: this is a useful number to have handy for a fast check of announced plans to reduce carbon dioxide emissions for the sake of climate change. I recommend you write it down on a scrap of paper and tape it to your monitor--I did!).

With that number in hand, all we need to do is divide:

Three hundred mmtCO2 (saved by everyone in the United States converting to vegetarianism) divided by 1,767,250 mmtCO2/°C equals 0.0002°C.  This is the amount of global warming avoided each year if all Americans become vegetarians. Two ten-thousandths of a degree.

If we were to stick to this vegetarian diet between now and the end of the 21st century, we’d collectively help to keep global temperatures two-hundredths of a degree below where they’d otherwise be.

Seems like even if I were worried about future climate change and wanted to “do something” about it, ridding my table of steak wouldn’t be high on the list.