Updated: March 4, 2015

Earth Deeds offers innovative online tools for understanding and then transforming carbon footprints through supporting sustainability projects.  We help groups and individuals

(1) make sense of their CO₂ emissions related to specified events, and

(2) build resiliency and sustainability within communities that matter to them.

This document outlines the assumptions and methodology that underlie Earth Deeds’ Carbon Footprint Calculator. All carbon calculators include a margin of error, but we strive to use the best available data and assumptions to provide the best estimate of emissions possible.  We rely heavily on the methodology outlined in the UK Government’s Department for Environment, Food, & Rural Affairs (DEFRA) in their July 2013 Methodology Paper for Emissions Factors^[1].  DEFRA’s guidelines on GHG emissions calculations are considered to be a standard of good practice within the voluntary carbon market.  Earth Deeds annually updates its methodology based on DEFRA’s guidelines and other industry data and seeks  feedback by experts in the field. Please send any feedback and suggestions to support@EarthDeeds.com. 

Most web-based carbon calculators measure individual’s annual emissions. Earth Deeds calculator focuses on the travel emissions for individual or group events (e.g. study abroad programs, weddings, conferences).  Over time, we intend to incorporate additional carbon footprint categories (e.g. food, electricity, heating) and environmental impacts (e.g, toxic waste, water usage) so users can better understand and acknowledge the emissions and impacts from their everyday activities.

Flight Emissions

The full calculation to measure flight emissions is as follows:

CO₂e = GCD x EF x CF x #P x #L x UF* x RFI*

where

GCD = Great Circle Distance

EF = Emissions Factor

CF = Class Factor

#P = Number of Persons

#L = Number of Legs

UF* = Uplift Factor (*optional)

RFI* = Radiative Forcing Index (*optional)

Let’s walk through these factors one by one.

Great Circle Distance

“Great Circle” refers to the shortest distance between two points on a sphere, measured along the surface of the sphere (as opposed to a straight line through the sphere's interior).^[2]

Emissions Factor

DEFRA develops emissions factors based on typical aircraft fuel burn over trip distances listed in the EMEP/CORINAIR Emissions Inventory Guidebook.^[3]  These factors account for methane (CH₄) and nitrous oxide (N₂O) in addition to Carbon Dioxide (CO₂) and express them in units of metric tonnes of CO₂ equivalent (CO₂e).  So in most cases results are slightly higher than if only calculating CO₂.

The 2012 Guidelines to DEFRA/DECC’s GHG Conversion Factors for Company Reporting^[4] categorizes UK flights into three distance brackets: “Domestic”, “Short-Haul”, and “Long-Haul”^[5].  “Domestic” is obviously not a useful category outside of the UK due to the varying sizes of countries, so we have recategorized these distance brackets as “Short-Haul”, “Medium-Haul”, and “Long-Haul.”

Table 1: Emissions Factors within three distance brackets

Administrators of Teams within colleges or universities that are using the Clean Air - Cool Planet Campus Carbon Calculator have the option to use CA/CP’s single air travel emissions factor of 0.524804879 kg CO₂e/passenger mile, which includes a 2.7 Radiative Forcing Index.^[7]

Class Factor

Economy, Business, and First Class seating take up varying amounts of space on airlines, which affects the total number of potential passengers they can carry and the percentage of GHG emissions they are responsible for.  DEFRA’s 2008 update reviewed seating configurations on 24 aircraft variants and suggested the following average conversion factors for different seat classes:

Number of Persons

This simply allows users to calculate emissions for multiple persons traveling on the same flights.

Number of Legs

This allows users to specify whether a flight is One-Way or Round-Trip.  Obviously, Round-Trip flights will be double the emissions of a One-Way flight.

Uplift Factor

Flights never quite follow Great Circle paths between airports.  An 8% “Uplift Factor” is added to account for circling and non-direct routes.^[8]

Radiative Forcing Index (Optional)

Atmospheric greenhouse effects are caused by more than direct CO₂ emissions from fuels, especially at high altitudes (e.g. contrails, water vapor, NOx emissions).  While there is active research on this Radiative Forcing Index, there is not a consensus on a figure, so Team Administrators have the option to choose amongst several commonly used multipliers:

Ground Transportation Emissions

Car

The basic calculation is

kg CO₂ = (kg CO₂ / gallon) x <# miles> / (miles / gallon)

where  kg CO₂ / gallon = 8.887^[13]

miles / gallon = <user input> or 23.1^[14] default (CA-CP uses 24.17)

so        kg CO₂ = 8.887 / <user input> or 23.1^[15] default (CA-CP uses 24.17)

Train

The basic calculation is

kg CO₂ / passenger mile = MMBtu / pass. mile x kg CO₂ / gallon x gallon /MMBtu

where  MMBtu / passenger mile = 0.001628^[16]

kg CO₂ / gallon = 8.887^[17]

gallon /MMBtu = 8.772^[18]

so        kg CO₂ / passenger mile = 0.1269

Bus

The basic calculation is

mT CO₂ / passenger mile = MMBtu / pass. mile x mT CO₂ / gallon x gallon /MMBtu

where  MMBtu / passenger mile = 0.003343^[19]

kg CO₂ / gallon = 8.887^[20]

gallon /MMBtu = 8.772^[21]

so        mT CO₂ / passenger mile = 0.2606

In each case, the emissions generated = emissions factor X distance

Fuel