Scientists at the University of Manchester have found a surprising global warming culprit – sandwiches. In the first study of its kind, the researchers carried out an in-depth audit of various sandwiches throughout their life cycles and found the triangular meals could be responsible for the equivalent annual carbon emissions of 8.6 million cars in Britain alone.

In 1762, or so the story goes, the fourth Earl of Sandwich rocked the culinary world when he couldn't be bothered to leave the gambling table to eat and ordered the servants to just stick some meat between two slices of bread for him. Since then, the modern sandwich has become one of the most popular of food formats.

According to the British Sandwich Association (BSA), the United Kingdom spends £8 billion (US$11.3 billion) annually on 11.5 billion sandwiches, with half made at home and the other half bought at shops, supermarkets, kiosks, and service stations. To better understand the environmental impact of all these sarnies, the Manchester team looked at over 40 different sandwich types, recipes, and combinations as well as how they are made, packaged, transported, and stored. In addition, they considered the waste produced in making them, as well as the stale, rotten, or simply outdated sandwiches that are thrown away.

What the researchers found was that not all sandwiches are created equal and that some varieties have larger carbon footprints than others. The highest footprint was found in premade, prepackaged, all-day-breakfast sandwiches. These contain eggs, bacon, and sausage and are kept packaged and refrigerated until sold and eaten – all of which is estimated to add up to 1,441 g (3.18 lb) of carbon dioxide equivalent, or roughly the same as driving a car for 12 miles (19 km).

By contrast, the smallest footprint is that of a homemade ham and cheese sandwich. Overall, making your sandwiches at home potentially halves the carbon emissions compared to their prepackaged equivalents.

According to the team, a number of factors affect the sandwich's carbon footprint. Ingredients is one of them, with items like meat in general and pork in particular, cheese, prawns, lettuce, and tomatoes being particularly large footprint culprits. Producing these ingredients, as well as the bread and condiments, can account for 37 to 67 percent of the carbon dioxide produced. Other factors are the packaging, which makes up 8.5 percent of emissions, transportation (especially in refrigerated trucks) for 4 percent, and refrigeration at point of sale making up another 25 percent.

The Manchester researchers aren't anti-sandwich, but they do say that changing recipes and packaging while reducing waste could result in a 50 percent drop in sandwich-related carbon emissions. Along with the BSA, they claim that something as simple as reforming the sell-by-date system could save over 2,000 tonnes of sandwiches in Britain being wasted each year.

"We need to change the labeling of food to increase the use-by date as these are usually quite conservative," says team member Professor Adisa Azapagic. "Commercial sandwiches undergo rigorous shelf-life testing and are normally safe for consumption beyond the use-by date stated on the label."

The research was published in the Journal of Sustainable Production and Consumption.

Source: University of Manchester