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Methodology

Calculations

GHG Intensity

Greenhouse Gas Intensity (yield-scaled emissions) (unitless) = Emissions (Mg CO2 eq/acre/yr) / Total Annual Yield (Mg/acre/yr)Total Annual Yield (Mg/acre/yr) = Average NASS yield (tons/acre)(or user entered yield) * Harvests per year * 0.91 (Mg/ton)

GHG per field

Total Field Emissions (Mg CO2 eq/yr) = Emissions (Mg CO2 eq/acre/yr) * Acres

Units

Model-simulated carbon sequestration and greenhouse gas emission estimates are given in Mg CO2 eq per year, where:

Mg = Megagrams (same as Metric Tonnes)
Megagrams or Metric Tonnes are similar to English (or ‘short’) tons;
0.91 Megagram (Metric Ton) = 1 English (short) tons

CO2 eq = Carbon Dioxide Equivalents
Carbon dioxide equivalent is a common measure used to compare the emissions/sequestration from various greenhouse gases, based upon their global warming potential. Carbon dioxide equivalents are used in COMET-Planner to allow users to compare emissions of carbon dioxide, nitrous oxide and methane in standardized units.

Global Warming Potential

A Global Warming Potential (GWP) is assigned to each greenhouse gas and reflects the climate forcing of emissions of one kilogram of a GHG, relative to one kilogram of carbon dioxide (CO2), over a defined period of time. The Intergovernmental Panel on Climate Change (IPCC) defines GWPs for GHGs in their assessment reports, which have changed slightly across assessments. COMET-Planner relies on GWPs cited in the IPCC Fourth Assessment Report (IPCC 2006) (Table 1).
Table 1. Global Warming Potential (GWP) of greenhouse gases (GHG) reported in COMET-Planner.
_Global Warming Potential (GWP) over 100 years
Carbon Dioxide CO21
Methane CH425
Nitrous Oxide N2O298

Terminology


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