Our contributions to the greenhouse effect via the food we eat is touched upon every now and then by media and public debate. Vegetarians usually blame meat eaters and buying local is touted as an obvious solution. It's a bit more complicated than that so this article sums up the results from a scientific study on exactly this subject. These numbers, details and recommendations need more attention. Not just to heighten the level of discourse but because as they say:

"Current trends in food choices point toward increased environmental effects."

Some of us may be seeing more and more environmentally friendly and affordable choices. Perhaps we're just looking for them which the majority still isn't?

The Greenhouse built from food

Producing food is one of the basic human activities. In any form it is a process of consumption - even ancient slash and burn agriculture involved the removal of an ecosystem carbon sink (the forest) - but some forms are a lot less straining on our resources than others. One meal can emit nine times as much greenhouse gas as another of similar caloric content. How so?

While carbon dioxide (CO₂) is the most important greenhouse gas (GHG) significant contributions are also made by methane (CH₄, ~14%-25% of emissions [2 , 3]) and nitrous oxide (N₂O, ~8% of emissions [3]). Methane is a product of natural materials decomposing without oxygen present - the occasional tree that dies and fall into a lake (naturally occurance of rot under water contributing miniscule GHGs), from the farts of many plant eating animals (due to their special cellulose digestion but significant contributions from industrial breeding only), from storage of manure (again: low oxygen rot) and from growing rice in flooded conditions (low oxygen and microorganisms). Nitrous oxide is produced by microbial transformation in soils and manure - especially when plenty of nitrogen is present. Nitrogen is often in local surplus from over-fertilization but it is actually also a by-product of the manufactur of fertilizer.

So, even if our food production lowered its emissions of CO₂ it'd still feed the greenhouse effect. Currently agriculture is the main source of the increase in atmospheric methane (~50%) and nitrous oxide (~60% to much higher in [3]). I'll skip the math in the middle and go straight to some dos and don'ts (mostly specific to a Western consumer but quite general).

Eat less red steaks

Emission of methane is particularly tied to the large scale production of meat (and consequently the dairy "by-products"... and rice). Livestock and their manure is guilty of about one twentieth (1/20) of the total GHG emissions. Cattle is the main problem because if its extreme emissions of methane by enteric fermentation. So, although pigs emit more methane via their manure, cattle in total emits about 3.8 times as much non-CO₂ GHG per carcass weight. Per kilo of final edible product it accumulates to 30 kilos of CO₂ equivalents (the measure of comparison between foods from here).

"[...] the consumption of 1 kg domestic beef [...] represents automobile use of a distance of ~160 km (99 miles)."

Don't even think about flying in that Argentine steak.

Of course, beef has good proteins. But comparing the GHG-wise efficiency of beef as a means of protein production to other food products it is actually the least effective. We can get our proteins from cereals, legumes and certain fish without causing climate change.

Don't eat the cod

One fish we shouldn't rely on for protein, though, is the cod. Well to begin with it's on the verge of extinction due to over-fishing and warming waters (at least in the Baltic and North Seas, marine ecologists predict it may reestablish itself in the Barents Sea [4]). But for each kilo of cod caught about 9 kg (yes nine kilos) of GHGs are emitted because trawling for them is fuel-intensive. This makes cod about as climate unfriendly as pork.

Although use of fossil fuel is increasingly "punished" (discouraged financially) and promises of protection of endangered species are handed out left and right cod fishing is profitable due to heavy subsidies by the European Union.

And things are relative: While I may have portrayed pork as a reasonable substitute for beef above, cod and pork emits approximately the same amount of GHGs (8.8 to 9.3 kg CO₂ equivalents).

The tropics are a spice

The flying Argentine steak is of course nasty. But basically, flying around with our nutrients is just not very smart. Anything flown from one half of the world to another will have a very bad GHG budget. Even fresh fruit; each kilo of which leaves 11 kilos of CO₂ right in the atmosphere if transported by plane. Many of our primary exotics - bananas, oranges - are shipped in by boat though, which is much, much more carbon friendly than planes.

The good solution is to eat locally produced food that doesn't require much transport at all. Should be common sense, really. Such products also has less need for demanding storage and temporary processing.

Consider the cheese and eggs too

Domestically produced cheese emits about as much GHG CO₂ equivalents as tropical fruits. And although a on a diffent scale entirely even eggs have a less than impressive figure (~23% of that of cheese). On the one hand especially eggs, however, are a source of protein. On the other hand both products are probably a bit too prevalent in many Western diets for other general health and nutritional reasons (fats, cholesteroles, salmonella).

There are many pros and cons to consider. Do we compose the climate friendly recipe by eating only low GHG emitting foods? Or do we just adjust our diets a little bit here and there? Besides preferences and willingness to change, one important thing to consider is our need for protein. Let's face it: We're not going to convert to hut dwelling veganism all of us just yet.

The perfect recipe?

About those 'little changes' first: Chicken production emits only about 4.3 kg CO₂ equivalents per kilo of meat. So, while still polluting, it could substitute some other meat meals while significantly lowering GHG emissions. (Small scale chicken production also holds some additional benefits such as pest control in plantations and food waste recycling. Chicken also lives anywhere in the world.) It is a relatively efficient source of proteins (~50 grams per kg GHG).

Another "substitute food" - having annoyed the cod fans above, perhaps - could be herring. At least in countries with herring rich waters. Fishing for herring is much less fuel demanding than fishing for cod. Thus, it also becomes a very efficient source of proteins (~145 grams per kg GHG).

Speaking of protein efficiency there is one clear winner: domestically produced whole wheat (~160 grams per kg GHG due to only 0.63 kg CO₂ equivalents per kilo of food).

Secondly, soy need being mentioned as it even after shipping by boat (0.92 kg CO₂ per kilo of food emitted) it delivers some 120 grams of protein per kg GHG emitted. Almost as good a budget goes for Italian pasta: compared to soy it additionally emits a bit of nitrous oxide but still delivers about 50 grams of protein per kg GHG emitted.

At last, the clear winners: fresh carrots, potatoes and honey (in north Europe at least). These foods emit very little GHGs (0.42, 0.45 and 0.46 kg CO₂ eqivalents of GHGs per kilo of food emitted respectively). They also provide some source of protein as well as other important nutritional ingredients. And honey is deliciously sweet.

Also, honorable mention to apples. The ones in your garden especially, but even when sailed in by boat the GHG budget is OK.

It is important to remember though, that this study didn't investigate every crop and livestock known to man, only a select set of representative and common choices. Pleas do comment with suggestions for other foods to avoid or prefer. Or even better: An actual recipe of low GHG emissions.

And finally: I personally don't really like either cod, herring, chicken or cheese myself. But I'm not vegetarian either as I really like beef, milk, eggs and other not too glorious foods unmentioned in this research (coffee to begin with). On a positive note, I love apples and honey. But I just summed up a research article - not advertising my tastes here. As may have been evident, I'm no cook either.

One reflection made by the authors is the possibility of forcing fast food producers to "extend" their beefs with plant proteins. Actually, this could have a major beneficial impact. They also propose more information (propaganda) to the public about those dietary changes that will be beneficial to both human as well as environment.

Sources:

First of all...

Carlsson-Kanyama, A., & Gonzalez, A. (2009). Potential contributions of food consumption patterns to climate change American Journal of Clinical Nutrition, 89 (5), 1704-1709 DOI: 10.3945/ajcn.2009.26736AA

Additionally...

• [2] Major methane emitter identified in Asian rice fields
• [3] World Resources Institute
• [4] North Sea cod 'doomed by climate change'

This post was chosen as an Editor's Selection for ResearchBlogging.org