Greenhouse gas (GHG) emissions are tightly coupled to the human diet, and food production systems contribute anywhere between 19-29% of human-related emissions globally.  There is, however, a wide difference in the amount of energy used and, hence, the embodied GHGs – i.e., the carbon footprint – associated with the life cycle of individual food products (see Tables 1 and 2 for examples, with differing study types). The largest net food-related carbon footprint is associated with ruminants, typically beef and mutton, the increasing consumption of which is considered to be having global scale consequences.    The carbon footprint per unit of product for most seafood, though far less than that of livestock,    is still significant, particularly in relation to other food products (Tables 1, 2).
Editor’s note: Steve Gaines, the dean of the UCSB Bren School of Environmental Science and Management, compares the climate impacts of protein systems, and envisions a world in which best practices in fisheries and aquaculture can sustainably meet the protein needs of a growing global population when included in a diet heavy in vegetables. In order to achieve such goals, the seafood industry must first understand the broad set of impacts fishing and aquaculture can have on the planet, and innovate to produce seafood in a way that can be sustained for generations to come.
Table 1. Mean food production emissions of greenhouse gases (from )
Carbon emissions (mean ± standard error of the mean)
g/kcal g/serving g/g-protein
|wheat||0.06 ± 0.009||5.2 ± 0.86||1.2 ± 0.14|
|fruits – temperate||0.10 ± 0.02||6.4 ± 1.2||n/a|
|vegetables||0.68 ± 0.25||14.0 ± 3.5||n/a|
|pulses||0.02 ± 0.002||1.9 ± 0.22||0.25 ± 0.04|
|eggs||0.59 ± 0.03||24.0 ± 1.0||6.8 ± 0.29|
|dairy||0.52 ± 0.04||74.0 ± 2.5||9.1 ± 0.3|
|fisheries – non-trawling||1.6 ± 0.25||40.0 ± 5.7||8.6 ± 1.3|
|fisheries – trawling||4.8 ± 1.3||108.0 ± 29.0||26.0 ± 6.7|
|aquaculture – non-recirculating||2.0 ± 0.41||60.0 ± 11.0||12.0 ± 2.3|
|aquaculture – recirculating||4.4 ± 1.9||160.0 ± 75.0||30.0 ± 14.0|
|poultry||1.3 ± 0.05||52.0 ± 2.1||10.0 ± 0.39|
|pork||1.6 ± 0.1||61.0 ± 3.6||10.0 ± 0.61|
|ruminant meat||5.6 ± 0.41||330.0 ± 18.0||62.0 ± 3.4|
Table 2. Carbon footprint of protein rich products per kilogram of product (from )
|Food type||Carbon footprint (kg CO2-eq kg-1)|
|pulses (dry)||1 – 2|
|meat substitute (vegetal)||1 – 2|
|milk||1 – 2|
|eggs||2 – 6|
|poultry||2 – 6|
|meat substitute (with egg or milk protein)||3 – 6|
|pork||4 – 11|
|seafood (aquaculture)||3 – 15|
|cheese||6 – 22|
|seafood (fisheries)||1 – 86|
|beef||9 – 129|
|mutton||10 – 150|
A useful indicator to compare energy efficiency among different production sectors is the energy return on investment (EROI), expressed as the ratio of energy produced to amount of energy used. In terms of food production the EROI typically measures the protein output by the energy required to produce it, i.e., fuel combustion. As can be seen in Table 3 there is a wide range in the kilocalories (kcal) of fossil fuel required to produce one kcal of edible protein across different production systems, even for the same species. Of the examples provided broiler chickens in the U.S. are the most energy efficient (i.e., to produce one kcal of edible chicken protein requires an energy investment that is four times greater) while intensively farmed shrimp in Thailand are the least efficient (i.e., one kcal of protein requires about 71 times the energy investment). For global fisheries one kcal of edible protein requires an estimated energy investment that is 12.5 times greater.
Table 3. Edible protein EROI from various animal-derived protein sources (from      )
|Livestock/animal products (U.S.)||Fisheries||Aquaculture|
|Chicken 25.0||EU fisheries 11.0||Mussel (longline culture, Scandinavia) 10.0-15.0|
|Turkey 10.0||Global fisheries 8.0||Tilapia (extensive pond culture, Indonesia) 13.0|
|Pork 7.1||Atlantic salmon (intensive net-pen, Norway) 8.1|
|Milk 7.1||Tuna (purse seine) 14.0||Atlantic salmon (intensive net-pen, Canada) 6.8|
|Eggs 2.6||Tuna (longline) 5.9||Atlantic salmon (intensive net-pen, Chile) 6.4|
|Beef 2.5||Tuna (pole and line) 4.3||Shrimp (semi-intensive, Ecuador) 2.5|
|Lamb 1.8||Shrimp (intensive, Thailand) 1.4|
Seafood’s carbon footprint
The carbon footprint of fisheries – up to the point of landing – includes, for example, emissions associated with vessel construction, fuel production and fuel use and refrigeration, with fuel use dominating overall emissions. For that of aquaculture – to the point before processing – the main carbon footprints are associated with farm operation, capture and reduction of wild fish (for feed) and feed processing. The full carbon footprint for both then also includes processing, packaging, storage, distribution, retail, consumer use and disposal, though many of these components are at present only rarely included in emission inventories.
Determining the carbon footprint of food is typically accomplished via Life Cycle Assessment (LCA), a widely-used and standardized analytical framework used for assessing environmental impacts and emissions along the life cycle of products, processes and services.  While the LCA approach can provide a high level of detail about, for example, a particular fishery or fishery product, a number of factors currently make it difficult to make reliable comparisons among food products that have been produced from a range of different sectors (e.g., livestock, vegetables, seafood) and regions under varying conditions (e.g., climatic, infrastructural) with often widely different post-production life cycle trajectories.  
The carbon footprint of seafood is also under considerable flux. Already the most highly traded food commodity internationally marine foods are increasingly being sourced further from markets, adding to transportation and refrigeration emissions. GHG emissions associated with aquaculture are increasing as production expands, though advances in feed formulation are likely to substantially reduce energy requirements per product unit. Meanwhile, the declining state of fish stocks implies increasing fuel use if catch levels are to be maintained. The fuel expenditure associated with fish capture may also increase under a changing climate as stocks redistribute further offshore and/or towards the poles as they track cooler water temperatures. On the other hand, emission-mitigating practices and technologies – as informed by LCAs – are being developed and implemented; these may be particularly important if seafood waste – with its embodied carbon footprint – is also reduced.
Carbon footprints and seafood diets
Dietary change away from meat-heavy diets has been shown to reduce GHG emissions.   A recent major study concluded that if global-average diets change as per projected income growth (i.e., are income-dependent) then per capita dietary GHG emissions from food production would increase 32% by 2050 (relative to 2009). That increase would be 30% less under a Mediterranean diet, 45% less under a pescetarian diet (i.e., vegetarian diet that includes seafood) and 55% less under a vegetarian diet.
Further, when combining the 32% per capita increase in emissions noted above with the population increase of 36% that is expected by 2050 (relative to 2009) an estimated 80% net increase in global GHG emissions would emanate from food production. In contrast, there would be no net increase in food production emissions by 2050 if the global diet had transitioned instead to the average of the Mediterranean, pescetarian and vegetarian diets.
The rather striking impacts of dietary choices are also seen in a recent study which looked at self-selected diets of meat-eaters and those of fish-eaters, vegetarians and vegans in the United Kingdom, and adjusted to a 2,000 kcal diet and for age and sex. As can be seen in Table 4 GHG emissions associated with diets including fish (and no meat) and those that are fully vegetarian are remarkably similar; furthermore, emissions associated with both are substantially less than those diets containing meat.
Editor’s note: So the challenge appears to be two-fold: How can we influence and reinforce shifts toward fish- and vegetable-based diets currently in their early stages; and how will we innovate to ensure best practices in seafood production to meet global demand sustainably?
Table 4. Mean greenhouse gas emissions per 2,000 kcal by diet type – United Kingdom (from )
|Diet type||Mean dietary GHG emissions (kgCO2e)|
|High meat-eaters (≥100 g/day)||7.19|
|Medium meat-eaters (50–99 g/day)||5.63|
|Low meat-eaters (<50 g/day)||4.67|
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