A lotta lentils.
As noted earlier, I am committing to try living a 1.5° lifestyle, which means limiting my annual carbon footprint to the equivalent of 2.5 metric tonnes of carbon dioxide emissions, the maximum average emissions per capita based on IPCC research. That works out to 6.85 kilograms per day.
According to the IGES/Aalto University study on the 1.5 degree lifestyle, the three "hot spots" for personal carbon emissions are our housing: how and where we live; our transportation: how we get around (discussed here); and our food: what we eat.For me, food may well be the hardest of all. First of all, the data are all over the map. Take a cheeseburger. One source says it has a footprint of 10 kg of CO2; in his book How bad are the Bananas, Mike Berners-Lee says a 4 ounce burger has a footprint of 2.5 kg. For consistency I am going to use Berners-Lee's numbers wherever I can.
There are also less useful analyses, like this one from the Environmental Working Group, which measures the kilograms of CO2 per kilogram of consumed food. But as my daughter the cheesemonger explains, you might sit down for dinner and have an 8 oz steak, but almost nobody can down 8 oz of cheese; you really have to look at portion size.
A much better way to measure it is to look at the CO2 footprint per kilocalorie of food eaten, as Shrink that Footprint does. In their calculations, beef and lamb are still off the scale, but going vegetarian won't do it for you because dairy and even fruit is actually worse than chicken, fish or pork. This just isn't detailed enough.
In their summary look at diets, an average American diet blows the entire carbon budget for the year. But even a vegan diet is way more than I can afford to stay under 2.5 tonnes total.
The most detailed analysis of the carbon footprint of food was done by Poore and Nemecek, who found that the numbers are "highly variable and skewed environmental impacts." Beef can vary by as much as an order of magnitude, depending on how it is raised and what it is fed.
For many products, impacts are skewed by producers with particularly high impacts. This creates opportunities for targeted mitigation, making an immense problem more manageable. For example, for beef originating from beef herds, the highest-impact 25% of producers represent 56% of the beef herd’s GHG emissions and 61% of the land use (an estimated 1.3 billion metric tons of CO2eq and 950 million ha of land, primarily pasture)
So as a consumer, it is almost impossible to get a precise number. But there are basic principles, and the diet we will be following is:
- No beef or lamb
- Cut way back on other meats
- Smaller portions of cheese (an important part of our diet, our daughter is a cheesemonger and we get such good stuff)
- Cut way back on alcohol (2 units of wine, the recommended maximum per day, is half a kilogram! A martini is only 123 grams.)
- Seasonal and mostly local fruits and vegetables (and no airfreighted asparagus!)
I will still be measuring everything and, for numbers, will rely on Mike Berners-Lee's book or Rosalind Readhead's detailed food diary. And I really do think this will be the hardest part of the whole project.