Methodology

Understanding our data sources, calculations, and the assumptions behind our comparisons.

Primary Data Source

Our emissions data is derived from the comprehensive meta-analysis by Poore and Nemecek, published in Science in 2018:

Poore, J., & Nemecek, T. (2018). Reducing food's environmental impacts through producers and consumers. Science, 360(6392), 987-992.

This study analyzed data from approximately 38,700 farms and 1,600 processors, covering 40 food products that represent ~90% of global protein and calorie consumption.

View the original study

Emissions Calculation

All emissions are expressed as kg CO₂e per 100g of protein, allowing fair comparison across foods with different protein densities.

Formula:

CO₂e (kg) = E × (P / 100)

Where:

E = kg CO₂e per 100g protein (from dataset)
P = target protein in grams

What's Included in CO₂e

The emissions figures include greenhouse gases from:

Land use and land use change
Farm operations (fertilizers, machinery, livestock)
Animal feed production
Processing and packaging
Transport to retail

Retail, consumer transport, and cooking emissions are not included.

Understanding Data Ranges

The "low" and "high" values represent the 10th and 90th percentilesof global production, not minimum and maximum values.

This variation reflects differences in:

Geographic region and climate
Farming practices (conventional vs. organic, intensive vs. extensive)
Feed sources and efficiency
Land use change history
Supply chain efficiency

Beef shows particularly high variation because emissions depend heavily on whether production involves deforestation, the type of grazing system, and whether cattle are from dedicated beef herds or dairy herds.

Vehicle Equivalency Calculations

To provide intuitive context, we convert CO₂e differences into equivalent driving distances. These are rough approximations for illustration only.

Toyota Prius

Tailpipe emissions: 155 g CO₂/mile
Based on EPA fuel economy data for hybrid vehicles
Calculation: miles = (CO₂e in grams) / 155

Semi-Truck

Fuel economy: 6.5 MPG (range: 5-7 MPG)
Diesel CO₂: 10,180 g/gallon
Resulting emissions: ~1,566 g CO₂/mile
Calculation: miles = (CO₂e in grams) / 1,566

Important: These calculations show tailpipe emissions only. They do not include lifecycle emissions from vehicle manufacturing, fuel extraction, or refining. The comparison is meant to provide intuitive scale, not precise equivalence.

Meal Emission Calculations

Meal emissions are calculated by summing the emissions of individual ingredients, using per-kilogram emission factors derived from the same Poore & Nemecek dataset.

Proxy Ingredients

For ingredients not directly covered in the source research, we use proxies:

Condiments: averaged from similar processed foods
Tortillas: based on wheat/corn flour products
Mixed vegetables: averaged from common vegetables

Scaling Meals

When comparing meals on equal protein, all ingredients are scaled proportionally. This maintains the recipe's character while adjusting portion size.

Limitations & Caveats

1.Global averages only. Your local food may have significantly different emissions based on where and how it's produced.
2.No individual dietary advice. This tool compares emissions, not nutritional completeness or health outcomes.
3.Data from 2018. Production methods and supply chains may have changed since the original research.
4.Protein focus. Comparing on protein alone ignores other nutritional factors like vitamins, minerals, and fiber.
5.No local producer data. We cannot account for specific farms, brands, or regional production methods.

Additional Resources