Calculator Methodology

This page provides a summary of the methodology used in the SeaGrass Grow Blue Carbon Offset Calculator. We are refining our methodology on an ongoing basis to be sure our models reflect the best and most current science and that the results are as accurate as possible. While calculations of voluntary blue carbon offsets may change as the model is refined, the amount of carbon offset in your purchase will be locked as of the date of purchase.

Estimation of Emissions

For estimation of CO2 emissions, we worked to strike a balance between accuracy, complexity, and ease of use.

Household Emissions

Emissions from homes vary by geography/climate, size of the home, type of heating fuel, source of electricity, and several other factors. Emissions are calculated using energy consumption data from the U.S. Department of Energy (DOE) Residential Energy Consumption Survey (RECS). Home energy consumption by end use is estimated based on three parameters: Location of the Home, Type of Home , Heating Fuel. Using RECS microdata, energy consumption data were tabulated for homes in five climate zones of the US. The energy consumption for a particular type of home in the given climate zone, along with the specified heating fuel, was converted to emissions of CO2 using the emission factors described above—the EPA factors for fossil fuel combustion and the eGrid factors for electricity consumption.

Meat Diet Emissions

Greenhouse gas emissions associated with eating three kinds of meat—beef, pork, and poultry—are included in the SeaGrass Grow calculator. Unlike other emission sources, these emissions are based on the full lifecycle of the meat production, including production of feed, transportation, and the raising and processing of the livestock. A number of studies have been conducted on the life-cycle of greenhouse gas emissions associated with food consumption. Since some of these studies focus on only one type of food product or another, and the methodology often varies between studies, a single study using a consistent top-down approach to calculate emissions from meat consumed in the US was used for the calculator.

Office Emissions

Emissions from offices are calculated in a manner similar to those for homes. The underlying data comes from the U.S. Department of Energy’s Commercial Building Energy Consumption Survey (CBECS). The most recent energy consumption data made available (as of 2015) by the DOE is used for calculating these emissions.

Land-Based Transportation Emissions

Emissions from the use of public transportation are typically given in terms of mass of emissions per passenger-mile traveled. The SeaGrass Grow Calculator uses the emission factors provided by US EPA and others.

Air Travel Emissions

The SeaGrass Grow model estimates 0.24 tons CO2 per 1,000 air miles. CO2 emissions from air travel have a greater impact contributing to climate change because they are released directly into the upper atmosphere.

Emissions from Hotel Stays

Recent research on sustainability in the hospitality industry has resulted in surveys of energy consumption and emissions across a wide sample of hotels and resorts. The emissions include both direct emissions from the hotel itself, as well as indirect emissions from electricity consumed by the hotel or resort.

Vehicle Emissions

An average number of emissions by vehicle class is based upon U.S. EPA estimates. One gallon of gasoline emits 19.4 pounds of CO2 while a gallon of diesel emits 22.2 pounds.

Estimation of Carbon Offsets

Our calculation of blue carbon offsets — the amount of seagrass or equivalent that must be restored and/or protected to offset a given amount of CO2 — is determined by an ecological model made up of four major components:

Direct Carbon Sequestration Benefits:

The carbon sequestration that would accrue per acre of restored seagrass bed over the specified time span/lifetime of project. We use an average of literature values for the growth rate of seagrass and compare restored seagrass beds to unvegetated bottom, a scenario for what might happen in the absence of restoration. While minor damage to seagrass beds can heal in less than a year, severe damage can take decades to heal or may never fully heal.

Carbon Sequestration Benefits from Erosion Prevention:

The carbon sequestration that would accrue due to the prevention of ongoing erosion from the presence of the prop scar or other bottom disturbance. Our model assumes ongoing erosion each year in the absence of restoration on a rate based on literature values.

Carbon Sequestration Benefits from Prevention of Rescarring:

The carbon sequestration that would accrue due to prevention of rescarring of a particular area. Our model takes into account the fact that in addition to restoration, we will be simultaneously working to prevent the rescarring of the areas we restore through signage, education programs and other efforts.

Carbon Sequestration Benefits from Prevention of Scarring of Undisturbed/Virgin Areas:

The carbon sequestration that would accrue due to prevention of scarring of a particular undisturbed/virgin area. As indicated above, we will be working to prevent future scarring of areas we have restored. In addition, we will be working to prevent damage to undisturbed/virgin areas as well.

A key assumption in our model is that our restoration and prevention efforts are deployed over a long period of time — many decades — in order to ensure that the seagrass remains intact and the carbon is sequestered for a long period of time.

At present the output of our ecological model for offsets is not visible in the Blue Carbon Offset Calculator. Please contact us if you have any questions.