A low carbon diet refers to making lifestyle choices
to reduce the greenhouse gas emissions (GHGe) resulting from
energy use. It is estimated that the U.S. food system is responsible for at
least 20 percent of U.S. greenhouse gases. This estimate may be low, as it
counts only direct sources of GHGe. Indirect sources, such as demand for
products from other countries, are often not counted. A low carbon diet
minimizes the emissions released from the production, packaging, processing,
transport, preparation and waste of food. Major tenets of a low carbon diet
include eating less industrial meat and dairy, eating less industrially produced food in general,
eating food grown locally and seasonally, eating less processed and packaged
foods and reducing waste from food by proper portion size, recycling or composting.
Overall trends
In a 2014 study by Scarborough et al., the real-life diets
of British people were surveyed and their greenhouse
gas footprints estimated. Average greenhouse-gas emissions per day (in
kilograms of carbon dioxide equivalent) were:
- 7.19 for high meat-eaters
- 5.63 for medium meat-eaters
- 4.67 for low meat-eaters
- 3.91 for fish-eaters
- 3.81 for vegetarians
- 2.89 for vegans
Background on diet and greenhouse gas emissions
In the U.S., the food system emits four of the greenhouse
gases associated with climate change: carbon
dioxide, methane,
nitrous
oxide, and chlorofluorocarbons. The burning of fossil
fuels (such as oil and gasoline) to power vehicles that transport food for
long distances by air, ship, truck and rail releases carbon dioxide (CO2), the
primary gas responsible for global warming. Chlorofluorocarbons (CFCs) are
emitted from mechanical refrigerating and freezing mechanisms – both
staples in food shipment and storage. Anthropogenic methane emission sources
include agriculture (ruminants, manure management, wetland rice production),
various other industries and landfills. Anthropogenic nitrous oxide sources
include fertilizer, manure, crop residues and nitrogen-fixing crops production.
Methane and nitrous oxide are also emitted in large amounts from natural
sources. The 100-year global warming potentials of methane and nitrous oxide
are recently estimated at 25 and 298 carbon dioxide equivalents, respectively.
Steinfeld et al. estimate that livestock production accounts
for 18 percent of anthropogenic GHG emissions expressed as carbon dioxide
equivalents. Of this amount, 34 percent is carbon dioxide emission from
deforestation, principally in Central and South America, that they assigned to
livestock production. However, deforestation associated with livestock
production is not an issue in many regions. In the US, the land area occupied
by forest increased between 1990 and 2009 and a net increase in forest land
area was also reported in Canada.
Of emissions they attribute to livestock production,
Steinfeld et al. estimate that globally, methane accounts for 30.2 percent.
Like other greenhouse gases, methane contributes to global warming when its
atmospheric concentration rises. Although methane emission from agriculture and
other anthropogenic sources has contributed substantially to past warming, it
is of much less significance for current and recent warming. This is because
there has been relatively little increase in atmospheric methane concentration
in recent years The anomalous increase
in methane concentration in 2007, discussed by Rigby et al., has since been
attributed principally to anomalous methane flux from natural wetlands, mostly
in the tropics, rather than to anthropogenic sources.
Livestock sources (including enteric fermentation and
manure) account for about 3.1 percent of US anthropogenic GHG emissions
expressed as carbon dioxide equivalents. This EPA estimate is based on
methodologies agreed to by the Conference of Parties of the UNFCCC, with
100-year global warming potentials from the IPCC Second Assessment Report used
in estimating GHG emissions as carbon dioxide equivalents.
High carbon and low carbon food choices
Certain foods require more fossil fuel inputs than others,
making it possible to go on a low carbon diet and reduce one’s carbon
footprint by choosing foods that need less fossil fuel and therefore emit
less carbon dioxide and other greenhouse gases.
In June 2010, a report from United Nations Environment
Programme declared that a global shift towards a vegan diet was needed to
save the world from hunger, fuel shortages and climate change.
Cundiff and Harris write: "The American Dietetic
Association (ADA) and Dietitians of Canada position paper officially recognizes
that well-planned vegan and other vegetarian diets are appropriate for infancy
and childhood. The American Academy of Pediatrics concurs." However, care is
essential to ensure adequate nutrition with a vegetarian diet. For example,
there is evidence of higher frequencies of non-anemic iron deficiency among
vegetarians versus omnivores and lower zinc status of vegetarian children,
in addition to the need for vitamin B12 supplementation with vegan diets.
Statistically, a higher risk of dietary deficiency has been reported with vegan
diets. Risks associated with such diets for children are discussed by Jacobs
and Dwyer. Also, some studies indicate higher frequency of hypospadias among
children of vegetarian mothers.
Industrial v. pastured livestock
Beef
and dairy
cattle can be particularly high in their levels of greenhouse gas emissions.
Feed is a significant contributor to emissions from animals raised in Confined
Animal Feeding Operations (CAFOs) or factory farms, as corn or soy beans must
be fertilised, irrigated, processed into animal feed, packaged and then
transported to the CAFO. In 2005, CAFOs accounted for 74% of the world's
poultry production, 50% of pork, 43% of beef, and 68% of eggs, according to the
[Worldwatch Institute]. Proportions are significantly higher in developed
countries, but are growing rapidly in developing countries, where demand is
also growing fast. However, in the US, only about 11 percent of soybean acres
and 14 percent of corn acres are irrigated; in contrast, about 66 percent of
vegetable acres and 79 percent of orchard acres are irrigated.In 1995,
commercial fertilizer inputs averaged 11 pounds per acre for US soybean
production, versus 157 pounds per acre for US potato production. Soybean meal
for livestock feed is commonly produced after extraction of soybean oil (used
for cooking, food products, biodiesel, etc., so that only a fraction of
processing is assignable to feed. Such examples illustrate that issues relating
to irrigation, fertilization and processing for meat production should also be
of concern with regard to production of other foods.
In one study, grass-fed cattle were estimated to account for
40% less greenhouse emissions than CAFO cattle However, comparative effects on
emissions can vary. in a US study, lower GHG emissions were associated with
feedlot-finished beef production than with beef production on pasture and hay.Similarly,
a study in New Zealand concluded that environmental emissions per kg of beef
produced can be reduced by incorporating feedlot finishing in a beef production
system. Another factor to be considered is the role of a healthy pastoral
ecosystem in carbon sequestration. Rotational grazing of ruminants
(cattle, sheep, goats, etc.) and birds (chickens, turkeys, etc.) on untilled
pasture land promotes rapid topsoil accumulation, representing a major carbon
sink.
Because CAFO production is highly centralised, the transport
of animals to slaughter and then to distant retail outlets is a further source
of greenhouse gas emissions. However, this can be more or less compensated by
reduced transport of feed, where CAFOs are located in feed-producing areas.
In livestock production, emissions are reduced by feeding
human-inedible materials that might otherwise by wasted. Elferink et al. state
that "Currently, 70 % of the feedstock used in the Dutch feed
industry originates from the food processing industry." Among several US
examples is the feeding of distillers grains remaining from biofuel production.
For the marketing year 2009/2010, the amount of dried distillers grains used as
livestock feed (and residual) in the US amounted to 25.0 million metric tons.
Distance traveled and method of transit
Carbon emissions from transport account for 11% of the total
carbon emissions of food, of which the transportation from producer to consumer
accounts for 4%.However, "food miles" are a very misleading measure;
in many cases food imported from the other side of the world may have a lower
carbon footprint than a locally-produced equivalent, due to differences in
farming methods; "local food" campaigns may be motivated by protectionism
rather than genuine environmentalism.
When looking at total greenhouse gases (not just carbon
dioxide), 83% of emissions come from the actual production of the food because
of the methane released by livestock and the nitrous oxide due to fertilizer.
The word locavore describes a person attempting to eat a diet
consisting of foods harvested from within a 100-mile radius.
Some studies have criticized the emphasis on local food,
claiming that it romanticizes local production, but does not produce very much
environmental benefit. Transportation accounts for a relatively small portion
of overall energy consumption in food production, and locally produced food may
be much more energy intensive than food produced in a better area. Additionally
the emphasis on "inefficient" local producers over more efficient
ones further away may be damaging.
Processing, packaging and waste
Highly processed foods such as granola
bars come in individual packaging, demanding high energy inputs and
resulting in packaging waste.These products contribute up to a third of total energy
inputs for food consumption, as their ingredients are shipped from all over,
processed, packaged, trucked to storage, then transported to retail outlets. Bottled
water is another example of a highly packaged, wasteful food product. It is
estimated that Americans throw away 40 million plastic water bottles every day,
and bottled water is often shipped trans-continentally. Carbonated
water must be chilled and kept under pressure during storage and transport
so as to keep the carbon dioxide dissolved. This factor contributes greater
energy usage for products shipped longer distances. Drinking purified tap water
treated with an active carbon filter for taste (most imp. chlorine),
is a lower carbon choice.
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