Measuring GHG emissions

• The "Grass fed beef is carbon neutral because its circular" myth

• Since there are many different greenhouse gases, researchers often aggregate them into a common unit of measurement when they want to make comparisons.

• The most common metric is carbon dioxide equivalents (CO2e) which basically totals up CO2 emissions and then converts all other gases to the CO2 based on how damaging they are.

• 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.

• ‘Carbon dioxide-equivalents’ (CO2eq) aggregate the impacts of all greenhouse gases into a single 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 period for climate policy.

• To calculate CO2e one needs to multiply the amount 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 CO2. For example, the IPCC adopts a GWP100 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 CO2. This factor is 34 when climate feedbacks are included.

An example of how “equivalents” works

• Here's a different example of the intuition behind this: imagine you want to quantify how bad someone's entire lifestyle is for their risk of lung disease. We could convert each factor (their diet, their smoking, exposure to pollution) into “cigarette equivalents”. Imagine 1 hour in traffic has the same effect on lung cancer risk as smoking 1 cigarette, so it is 1 cigarette equivalent. Eating 100g of smoked meats also has the same lung cancer risk as smoking 1 ciggie, so 100g of smoked meats is 1 cigarette equivalent. We can now measure a person's lifestyle on a number of different metrics, convert them all into cigarette equivalents, and total them up to get a measure for how bad someone's lifestyle is overall.

GWP100 can be misleading

The IPCC has also recognised this misapplication of GWPs, stating:

“GWP100 is not well-suited to estimate the cumulative effect on climate from sustained SLCF emissions [Short-lived climate forcers, including aerosols, methane and nitrogen oxides] and the resulting warming at specific points in time” [6].

The difficulty of accounting for methane

There is a current battle between the meat industry that like GWP* and everyone else, see GWP* is misleading environmental measure

Despite there being a debate on how to account for methane in climate metrics, it's worth noting that even excluding methane, animal products are far worse for the environment than plant foods: