Vegetarian Diet vs Avg US Meat Consumer
Brighter Planet did a report on the American Carbon footprint.
It gives the following averages for US diet types:
- omnivore - ~6500 lbs CO2 per person per year
- vegetarian ~5100 lbs CO2 per person per year
- vegan ~4400 lbs CO2 per person per year
That's over a 20% improvement for vegetarianism over a meat diet and over a 30% improvement for vegans (this assumes equal caloric intake). Note I eyeballed those numbers off graphs.
Also, fairly important, I saw no mention of emissions associated with deforestation from clearing land for pasture. This could be significant and imply a more significant GHG reduction from a vegetarian diet.
Vegetarian vs Avg Global Meat Consumer
A report undertaken by two World Bank environmental advisers, estimated that the global livestock industry (lifecycle supply chain) accounts for 51% of global CO2 emissions. This seems really high. The UN FAO put the figure at 18%, but report cited above includes respiration, land use change, undercounted methane, increased meat consumption between the dates of the reports (2002 and 2009), and several other smaller factors.
I couldn't find an emissions per calorie figure for the globe, however, the ratios probably aren't too different from above. What's important at the global scale is meat consumption now stands at 322 g/day/capita in the US. The global figure is 115 g/day/capita. That means the world outside of the US is relatively vegetarian. However, as incomes climb, consumers eat more meat (though at a diminishing rate).
All in all, the world is shifting towards a more meat dense diet and thereby raising food emissions significantly (stats above from UNEP GHG Emissions Associated with Meat Production.
Vegetarianism vs Locavorism
A paper from Environmental Science and Technology, which earned ACS honors for top paper in environmental policy, claims that 83% of food emissions are in production - only 11% of lifecycle emissions are caused by transportation. They conclude:
Shifting less than one day per week’s worth of calories from red meat and dairy products to chicken, fish, eggs, or a vegetable-based diet achieves more GHG reduction than buying all locally sourced food.
Shifting away from red meat, especially to a vegetarian diet, is a stronger lever towards reducing GHG emissions.
Importance of Livestock Feed
This could actually be pretty significant for beef. Haven't found a scientific figure, a prof from Dalhousie University claimed an interview with Science News, the significance could be on the order of 50%. That would make it competitive with some fruits and vegetables.
Relative emission intensities of meat products
The same report from Brighter Planet gives the following GHG intensities per calorie (g CO2/calorie) by food group:
- red meat : 11
- poultry: ~5.5
- fish ~ 7.5
- dairy ~ 6.5
- vegetables and fruits 5-6
- Vegetarianism has non-negligible GHG benefits (less so with poultry)
- The difference is most stark with red meat
- Differences in meat type and agricultural practices may be as significant as the difference between the average meat diet and vegetarianism.
- Composition of diet is more important than location of food sources.