In an era where climate change is a growing concern for individuals worldwide, understanding the carbon footprint of our dietary choices has become increasingly important. A significant portion of global greenhouse gas emissions comes from food production, making our diet a key factor in our environmental impact. This article explores how different foods contribute to greenhouse gas emissions and what dietary choices can effectively reduce your carbon footprint.
The Misconception of "Eating Local"
A common recommendation for reducing your diet's carbon footprint is to "eat local." While seemingly intuitive, this advice can be misleading. The idea behind it is that transporting food contributes significantly to its overall carbon footprint. However, for most foods, transportation accounts for a relatively small percentage of total emissions. The type of food you eat is far more critical than where it comes from.
Sources of Emissions in Food Production
To understand the true impact of our food choices, we need to examine the entire supply chain, from land use to transportation and packaging. A comprehensive meta-analysis of global food systems, conducted by Joseph Poore and Thomas Nemecek in 2018, provides valuable insights. This study analyzed data from over 38,000 commercial farms across 119 countries, comparing the total greenhouse gas (GHG) emissions per kilogram of various food products.
The study expressed GHG emissions in kilograms of carbon dioxide equivalents (CO2-eq), a metric that accounts for all greenhouse gases, including CO2, methane, and nitrous oxide, weighted by their global warming potential. The results revealed significant differences in the GHG emissions of different foods.
Animal-Based vs. Plant-Based Foods
One of the most striking findings of the study is the vast difference in GHG emissions between animal-based and plant-based foods. Producing one kilogram of beef, for example, emits 60 kilograms of CO2-eq, while producing one kilogram of peas emits only 1 kilogram of CO2-eq. In general, animal-based foods, particularly beef, lamb, and cheese, have a much higher carbon footprint than plant-based alternatives.
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Poultry and pork have lower footprints than beef and lamb but still higher than most plant-based foods. For most foods, the majority of GHG emissions come from land use change and farm-stage processes, such as fertilizer application and enteric fermentation (methane production in cattle stomachs). These two stages combined can account for over 80% of a food's total carbon footprint.
The Limited Impact of Transportation
Contrary to popular belief, transportation is a relatively small contributor to the overall carbon footprint of most foods, typically accounting for less than 10% of emissions. For major GHG emitters like beef, transportation can be as low as 0.5% of the total footprint. This holds true not only for individual food products but also for entire diets. Studies have shown that food transport accounts for a small percentage of emissions, while dairy, meat, and eggs contribute a much larger share.
Eating local beef or lamb, therefore, has a significantly higher carbon footprint than most other foods, regardless of where they are grown or shipped from. The location of production has minimal impact on the total emissions of these high-impact foods.
The Distance Factor: An Example with Beef
To illustrate the limited impact of distance on the carbon footprint of food, consider the example of beef. The average footprint of beef from a beef herd is approximately 60 kilograms of CO2-eq per kilogram of beef. Comparing the transport footprint of buying local beef versus importing beef from Central America (9000 kilometers away) reveals a negligible difference.
Transporting beef from Central America to the UK emits approximately 0.207 kilograms of CO2-eq per kilogram of beef, which is only 0.35% of the total footprint. Buying local beef, assuming zero transport emissions, reduces the footprint to 59.8 kilograms of CO2-eq per kilogram. The difference is minimal, highlighting that the primary factor driving beef's carbon footprint is the production process, not the distance it travels.
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The Trade-offs of Eating Locally
In some cases, eating locally can even increase emissions. Many foods can only be grown and harvested at certain times of the year in specific regions. To meet year-round consumer demand, three options exist: importing goods from in-season countries, using energy-intensive production methods like greenhouses, or employing refrigeration and preservation methods for extended storage. Studies have shown that importing goods can often have a lower footprint than local production using energy-intensive methods.
For example, importing Spanish lettuce to the UK during winter months can result in significantly lower emissions than producing it locally. Similarly, tomatoes produced in greenhouses in Sweden can use ten times as much energy as tomatoes imported from Southern Europe during their growing season.
The Exception: Air-Freighted Foods
While transportation generally has a limited impact on a food's carbon footprint, there is one significant exception: air-freighted foods. Although air freight accounts for a small percentage of food miles, it emits significantly more CO2-eq per tonne kilometer than other transportation methods.
Air-freighted foods are typically highly perishable items that require rapid transport to maintain freshness. Common examples include asparagus, green beans, and berries. Identifying air-freighted foods can be challenging, as they are rarely labeled as such. However, avoiding foods with a very short shelf-life and traveling a long distance can help minimize your consumption of air-freighted products.
Dietary Changes for a Lower Carbon Footprint
To effectively reduce your diet's carbon footprint, focusing on what you eat is more impactful than solely focusing on eating locally. Reducing your consumption of meat and dairy, particularly ruminant meat like beef and lamb, can significantly lower your environmental impact. Switching to chicken, pork, or plant-based alternatives can also make a substantial difference.
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Studies have shown that substituting less than one day per week's worth of calories from beef and dairy products with chicken, fish, eggs, or plant-based alternatives can reduce GHG emissions more than buying all your food from local sources.
The Low-Carbon Diet: Principles and Practices
A low-carbon diet is defined as any diet that results in lower greenhouse gas emissions. Key tenets of a low-carbon diet include eating a plant-based diet and minimizing the consumption of beef and dairy. Low-carbon diets vary across the world but generally emphasize unprocessed starches, grains, nuts, seeds, and legumes.
The Role of Vegetarianism and Veganism
Vegetarian and vegan diets have been shown to have the lowest carbon footprints compared to diets that include meat and fish. These diets rely heavily on plant-based foods, which require less fossil fuel input and land use than animal-based foods.
Food Waste and Packaging
In addition to dietary choices, reducing food waste and minimizing packaging can also contribute to a lower carbon footprint. A significant portion of food produced globally is wasted, leading to unnecessary emissions. Buying only what you need, using leftovers, and properly storing food can help reduce waste.
Highly processed foods often come in individual packaging, which requires high energy inputs and generates waste. Choosing foods with minimal packaging and opting for reusable containers can help minimize your environmental impact.
Case Study: Carbon Footprint of Diets in Poland
A recent study analyzed the carbon footprint of diets in Poland, comparing vegans, vegetarians, fish-eaters, and meat-eaters. The study found a decreasing trend in the carbon footprint corresponding to the degree of elimination of animal-derived products from the diet. Vegans had the lowest mean daily carbon footprint, followed by vegetarians, fish-eaters, and meat-eaters.
The study also found that hard and mozzarella cheeses had the highest contribution to the carbon footprint in vegetarians, while fish and seafood consumption had the greatest contribution in fish-eaters. Poultry, pork, and beef had the highest contribution in meat-eaters.