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      Global warming potential (GWP) and gas aggregation

      Description of how gases are aggregated

      What is global warming potential

      The Intergovernmental Panel on Climate Change (IPCC) defines Global Warming Potential (GWP) as a metric that quantifies the cumulative radiative forcing—i.e., the energy absorbed and retained in the Earth's atmosphere—resulting from the emission of a unit mass of a greenhouse gas (GHG) over a specified time horizon (e.g. 100 years), relative to the same mass of carbon dioxide (CO₂), which is assigned a GWP of 1.

      To apply GWP to emissions in agriculture, you convert each type of greenhouse gas (GHG) emitted (like methane and nitrous oxide) into a carbon dioxide equivalent (CO₂e) using the GWP values. This standardizes emissions across gases to a common unit so they can be summed and compared.

      GWP methodology

      Regrow uses IPCC AR6 for all upstream and on farm activity's GWP values.

      On field values via DNDC depend upon the product:

      • Sustainability Insights product uses AR6

      • MRV product uses AR5

      Regrow will be transitioning MRV/API over to AR6 on field, at which time this documentation will be updated. The remainder of this document will focus on up stream and on farm emissions activities and gas aggregation. 

      The steps Regrow takes to calculate CO2e using GWP

      1. For all activities, first calculate emissions – Identify how much CH₄, N₂O, and CO₂ the production of your crop releases.

      2. Pre-determine GWP values – All GWP values are defaulted for all gases with two different values for CH4.

      3. Multiply each gas by the selected GWP – This converts all emissions into kg CO₂-equivalent (CO₂e) per kg.

      4. Add – Combine the CO₂e values for a total.

      5. Use the total CO₂e – Report it, track changes, or compare with targets.

      AR6 GWP values and sources 

      Greenhouse gas

      Selection type

      GWP value

      Description of GWP assumptions

      Source

      CO2

      Default value

      1

      As the reference GHG species, GWP of CO2 is always 1 by definition.

      Table 7.15 in IPCC AR6 WGI Chapter 7

      N2O

      Default value

      273

      The radiative forcing effect of N2O, relative to CO2, over the 100-year integration time.

      Table 7.15 in IPCC AR6 WGI Chapter 7 (Table 7.15)

      CH4

      Default value for fossil

      29.8

      Identified in the IPCC AR6 as fossil and fossil – fugitive and process, which is an adjusted GWP for methane from fossil sources. This value is increased from 27.9 to reflect added radiative forcing from CO2 through oxidation of methane.

      It is calculated by increasing the “solely methane” value (27.9) to reflect the subsequent radiative forcing effect from CO2 added to the atmosphere through the oxidation of methane.

      Table 7.15 in IPCC AR6 WGI Chapter 7 (Table 7.15)

      CH4

      Default value for non fossil

      27

      Identified in the IPCC AR6 as non-fossil, biogenic, and fossil-combustion, which is an adjusted GWP for methane from non-fossil sources only — reduced from 27.9 to reflect IPCC’s assumption that 25% of the CH4 at the end of its atmospheric lifetime not oxidized to CO2 but will convert to formaldehyde and removed from atmosphere.

      Table 7.15 in IPCC AR6 WGI Chapter 7 (Table 7.15)

      CH4

      Not used

      27.9

      Identified in the IPCC AR6 as “methane”, it represents solely the radiative forcing effect of CH4, relative to CO2, over the 100-year integration time without any adjustment

      Table 7.SM.7 in IPCC AR6 WGI Chapter 7, Supplemental Material (Table 7.SM.7)
       
       Gases used from Ecoinvent

      Regrow uses Ecoinvent’s LCI results, emissions Exchange Names and corresponding amounts to provide each emission per gas. Each activity (ex. fertilizer production, etc.) will have multiple exchange emissions per gas of interest. All are taken from Ecoinvent and summed to get the final emissions.

      CO2 exchanges used

      • Carbon dioxide, fossil air, lower stratosphere + upper troposphereCH4 exchanges

      • Carbon dioxide, fossil air, non-urban air or from high stacks

      • Carbon dioxide, fossil air, unspecified

      • Carbon dioxide, fossil air, urban air close to ground

      CH4 exchanges used

      • Methane, fossil air, non-urban air or from high stacks

      • Methane, fossil air, unspecified

      • Methane, fossil air, urban air close to ground

      • Methane, from soil or biomass stock air, non-urban air or from high stacks

      • Methane, non-fossil air, non-urban air or from high stacks

      • Methane, non-fossil air, unspecified

      • Methane, non-fossil air, urban air close to ground

      N20 exchanges used

      • Dinitrogen monoxide air, low population density, long-term

      • Dinitrogen monoxide air, non-urban air or from high stacks

      • Dinitrogen monoxide air, unspecified

      • Dinitrogen monoxide air, urban air close to ground