9/13/2023 0 Comments Low carbon emissionsThis is not the case for plant-based foods, with the exception of rice. It also matters a lot for dairy production, and a reasonable amount for farmed shrimps and fish. If we removed methane their emissions would fall by around half. This is because cattle and lamb are what we call ‘ ruminants’, in the process of digesting food they produce a lot of methane. So, if we remove methane, the remaining footprint is 51 kgCO 2eq (shown in red).Īs we see, methane emissions are large for beef and lamb. Methane accounts for 49% of its emissions. The red and grey bar combined is therefore the total emissions including methane.Īs an example: the global mean emissions for one kilogram of beef from non-dairy beef herds is 100 kilograms of CO 2eq. The red bars show greenhouse emissions we would have if we removed methane completely the grey bar shows the emissions from methane. This chart compares emissions in kilograms of CO 2eq produced per kilogram of food product. 7 The study looks at the environmental impacts of foods across more than 38,000 commercially viable farms in 119 countries. 6Īs in my original post, this data is sourced from the largest meta-analysis of global food systems to date, by Joseph Poore and Thomas Nemecek (2018), published in the journal Science. In the visualization I compare the global average footprint of different food products, with and without including methane emissions. The question then is: Do these measurement issues matter for the carbon footprint of different foods? Are the large differences only because of methane? So CO 2eq footprints of foods which generate a high proportion of methane emissions – mainly beef and lamb – don’t by definition reflect their short-term or long-term impact on temperature. Methane’s shorter lifetime means that the usual CO 2-equivalence does not reflect how it affects global temperatures. 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 methane’s shorter lifetime (called GWP*), in an article in Carbon Brief here. Michelle Cain, Myles Allen and colleagues at the the University of Oxford’s Martin School lead a research programme on climate pollutants, which takes on this challenge. Researchers therefore develop new metrics and methods with the aim to provide a closer representation of the warming potential of different gases. ![]() This means there is often confusion as to how we should quantify the climate impacts of methane. 5 Methane therefore has a high impact on warming in the short term, but a low impact in the long run. This is in contrast to CO 2 which can persist in the atmosphere for many centuries. It has a very strong impact on warming in the short-term but decays fast. In contrast to CO 2, methane is a short-lived greenhouse gas. To understand why the conversion factor of 28 is criticised one needs to know that different greenhouse gases remain in the atmosphere for different lengths of time. ![]() For example, the IPCC adopts a GWP 100 value of 28 for methane based on the rationale that emitting one kilogram of methane will have 28 times the warming impact over 100 years as one kilogram of CO 2. To calculate CO 2eq one needs to multiply the amount of each greenhouse gas emissions by its GWP 100 value – a value which aims to represent the amount of warming that each specific gas generates relative to CO 2. ![]() More specifically, global warming potential over a 100-year timescale (GWP 100) – a timeframe which represents a mid-to-long term period for climate policy. ‘Carbon dioxide-equivalents’ (CO 2eq) aggregate the impacts of all greenhouse gases into a single metric using ‘global warming potential’. This is the metric adopted by the Intergovernmental Panel on Climate Change (IPCC) and is used as the official reporting and target-setting metric within the Paris Agreement. 2 The most common way to do this is to rely on a metric called ‘carbon dioxide-equivalents’. Since there are many different greenhouse gases researchers often aggregate them into a common unit of measurement when they want to make comparisons. In the box at the end of this article I discuss the debate on emissions metrics and the treatment of methane in more detail. Methane emissions have so far driven a significant amount of warming – with estimates ranging from around 23% to 40% of the total – to date. It could be argued that red meat and dairy have a much higher footprint because its emissions are dominated by methane – a greenhouse gas that is much more potent but has a shorter lifetime in the atmosphere than carbon dioxide. In this post I want to investigate whether these conclusions depend on the particular metric we rely on to quantify greenhouse gas (GHG) emissions.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |