Carbon Footprint of 1 Lb of Beef
Every bit I accept shown before, at that place are large differences in the carbon footprint of different foods. Beef and lamb, in particular, accept much college greenhouse gas emissions than craven,pork, or found-based alternatives.
This data suggests that the well-nigh effective way to reduce the climate impact of your diet is to eat less meat overall, especially red meat and dairy (see here).
Metrics to quantify greenhouse gas emissions
In this mail service I want to investigate whether these conclusions depend on the detail metric we rely on to quantify greenhouse gas (GHG) emissions. Information technology could be argued that ruby-red meat and dairy have a much higher footprint considering its emissions are dominated by marsh gas – a greenhouse gas that is much more potent but has a shorter lifetime in the atmosphere than carbon dioxide. Methyl hydride emissions have so far driven a significant amount of warming – with estimates ranging from around 23% to 40% of the total – to date.1
In the box at the end of this commodity I discuss the debate on emissions metrics and the treatment of methane in more item. Merely, here, I'll keep it brusk:
Since there are many unlike greenhouse gases researchers frequently aggregate them into a mutual unit of measurement when they want to make comparisons.ii The most common mode to do this is to rely on a metric chosen 'carbon dioxide-equivalents'. This is the metric adopted past the Intergovernmental Console on Climate change (IPCC); and is used as the official reporting and target-setting metric within the Paris Agreement.3
'Carbon dioxide-equivalents' (CO2eq) amass the impacts of all greenhouse gases into a unmarried metric using 'global warming potential'. More specifically, global warming potential over a 100-year timescale (GWP100) – a timeframe which represents a mid-to-long term flow for climate policy.
To calculate COtwoeq one needs to multiply the corporeality of each greenhouse gas emissions by its GWP100 value – a value which aims to represent the amount of warming that each specific gas generates relative to COtwo. For case, the IPCC adopts a GWP100 value of 28 for marsh gas based on the rationale that emitting one kilogram of methyl hydride will accept 28 times the warming touch over 100 years as one kilogram of CO2.iv
Methane is short-lived, COii is long lived: this makes aggregation hard
To understand why the conversion factor of 28 is criticised 1 needs to know that dissimilar greenhouse gases remain in the temper for unlike lengths of time. In contrast to CO2, methane is a brusk-lived greenhouse gas. It has a very strong impact on warming in the short-term simply decays fast. This is in contrast to CO2 which can persist in the atmosphere for many centuries.5 Methane therefore has a high impact on warming in the short term, but a low touch on in the long run. This means there is often confusion as to how we should quantify the climate impacts of methane.
Researchers therefore develop new metrics and methods with the aim to provide a closer representation of the warming potential of different gases.
Michelle Cain, Myles Allen and colleagues at the the University of Oxford's Martin Schoolhouse lead a research programme on climate pollutants, which takes on this challenge. Dr Michelle Cain, one of the lead researchers in this area, discusses the challenges of GHG metrics and the role of a new way of using GWP which accounts for marsh gas'due south shorter lifetime (called GWP*), in an article in Carbon Cursory here.
Methane'due south shorter lifetime means that the usual COii-equivalence does not reflect how it affects global temperatures. So CO2eq footprints of foods which generate a high proportion of methane emissions – mainly beef and lamb – don't by definition reflect their brusk-term or long-term impact on temperature.
How big are the differences with or without marsh gas?
The question then is: Do these measurement issues matter for the carbon footprint of different foods? Are the large differences only because of methane?
In the visualization I compare the global average footprint of different food products, with and without including methane emissions.half-dozen
As in my original mail, this data is sourced from the largest meta-assay of global food systems to date, past Joseph Poore and Thomas Nemecek (2018), published in the journal Science.7 The study looks at the environmental impacts of foods across more than than 38,000 commercially viable farms in 119 countries.
This chart compares emissions in kilograms of COiieq produced per kilogram of food product.
The ruby bars show greenhouse emissions we would have if we removed methane completely; the gray bar shows the emissions from marsh gas. The red and grey bar combined is therefore the total emissions including methyl hydride.
Every bit an instance: the global mean emissions for one kilogram of beefiness from non-dairy beefiness herds is 100 kilograms of COiieq. Methane accounts for 49% of its emissions. So, if we remove marsh gas, the remaining footprint is 51 kgCOtwoeq (shown in red).
Every bit nosotros see, methyl hydride emissions are large for beefiness and lamb. This is because cattle and lamb are what we call 'ruminants', in the process of digesting food they produce a lot of methyl hydride. If we removed methyl hydride their emissions would fall by effectually half. It also matters a lot for dairy production, and a reasonable amount for farmed shrimps and fish.
This is non the case for constitute-based foods, with the exception of rice. Paddy rice is typically grown in flooded fields: the microbes in these waterlogged soils produce methane.
This means that beefiness, lamb and dairy products are particularly sensitive to how nosotros treat methane in our metrics of greenhouse gas emissions. Few would debate that we should eliminate methyl hydride completely, but, equally explained, there is an ongoing fence equally to how to weigh the methyl hydride emissions – whether the gray bar should shrink or abound in these comparisons.
And then is it true that red meat and dairy only has a big carbon footprint because of marsh gas? As the cerise bars show it is not.
Although the magnitude of the differences change, the ranking of different food products does not.
The differences are nonetheless large. The average footprint of beef, excluding methane, is 36 kilograms of CO2eq per kilogram. This is nevertheless nearly four times the mean footprint of craven. Or 10 to 100 times the footprint of almost plant-based foods.
Where do the non-methyl hydride emissions from cattle and lamb come from? For most producers the primal emissions sources are due land use changes; the conversion of peat soils to agriculture; the land required to abound animal feed; the pasture direction (including liming, fertilizing, and irrigation); and the emissions from slaughter waste.
What virtually the impact of producers who are not raising livestock on converted land? Practice they take a low footprint? In our related commodity I look in detail at the distribution of GHG emissions for each production, from the lowest to highest emitters. When nosotros exclude marsh gas, the absolute lowest beefiness producer in this large global dataset of 38,000 farms in 119 countries had a footprint of vi kilograms of COiieq per kilogram. Emissions in this case were the result of nitrous oxide from manure; machinery and equipment; ship of cows to slaughter; emissions from slaughter; and nutrient waste material (which can be loftier for fresh meat). 6 kilograms of CO2eq (excluding marsh gas) is of form much lower than the boilerplate for beef, but still several times higher than near plant-based foods.
Comparing the footprints of protein-rich foods
Is information technology perhaps misleading to compare foods on the basis of mass? After all one kilogram of beefiness does not have the aforementioned nutritional value as one kilogram of tofu.
In the other visualization I therefore show these comparisons as the carbon footprint per 100 grams of protein. Once more, emissions from marsh gas are shown in grey; merely this time, emissions excluding methane are shown in blueish.
The results are again like: even if we excluded methyl hydride completely, the footprint of lamb or beefiness from dairy herds is v times higher than tofu; x times higher than beans; and more than twenty times higher than peas for the same amount of protein.
The weight we requite to methane matters for the magnitude of the differences in carbon footprint we run across between food products. Nonetheless, it doesn't alter the general decision: meat and dairy products however height the list, and the differences between foods remain large.
Boosted information: how to nosotros quantify greenhouse gas emissions?
Source: https://ourworldindata.org/carbon-footprint-food-methane
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