The Working Waterfront

How to best crunch the greenhouse gas numbers

Tools to calculate emissions are being refined and improved

Meghan Grabill
Posted 2021-08-04
Last Modified 2021-08-04

Carbon pollution, also known as greenhouse gas emissions, is detrimental to the current way of life on Earth. In 2003, Maine became a climate leader for the nation when it became the first state to enact legislation setting specific greenhouse gas (GHG) reduction targets. Since then, many other states have developed policies aimed at mitigating GHG emissions.

The first step in meeting climate reduction goals is to conduct a study of the state’s current and past GHG emissions.  Maine used 1990 as its baseline and set its reduction goals from that year. Maine will reduce its gross emissions by 45 percent by 2030 and 80 percent by 2050.

Measuring GHG allows Maine to determine if its actions are moving it closer to its reduction goals. Progress toward achieving these goals continues to be tracked through annual GHG inventories developed by the Department of Environmental Protection which are reported to the legislature in biennial reports.

While carbon sequestration is an important part of the story, it should not be seen as a way out of reducing emissions.

A GHG inventory is the process of estimating the amount of greenhouse gasses emitted by a given entity (state, organization, city, etc.) or sector during a period of time.

To compile these data, DEP relies on the State Inventory Tool provided by the federal Environmental Protection Agency. This tool, which also adheres to the Intergovernmental Panel on Climate Change guidelines, allows states to calculate a comprehensive and consistent total which is comparable to other states.

The tool is a computer module that combines federal- and state-sourced data to estimate total GHG emissions each year. Data used in the tool comes from many sources including facility-reported emissions, reported fuel use, and models.

Some of the emissions are difficult to pinpoint, like wood used for residential home heating, which is used by 10.7 percent of homes in Maine. To get this number the department relies on a survey that asks homeowners about the fuel they use to heat their homes.

“DEP is required by statute to compile and report greenhouse gas emissions for the state of Maine,” according to Stacy Knapp, emissions inventory section manager in DEP’s Bureau of Air Quality. “We try to be as transparent as possible with the data, including additional pieces of data where they might be helpful for some strategies or policy decisions.”

In May, DEP began a rulemaking public hearing to share and seek comment on its plans for updating and codifying the methods used to collect the data and report the findings.

The department will further increase transparency to the public by including additional reports like net GHG emissions. In the past, only gross GHG emissions were included. Researchers at the University of Maine have developed the State of Maine Carbon Budget to estimate current carbon sequestration, and DEP is collaborating with the university as it works to further improve methods for collecting this type of data.

Calculating the net GHG emissions requires determining the amount of carbon sequestration. Carbon is captured and stored (or sequestered) in the forests and along our coastline in saltmarshes, seagrasses, and seaweed, also known as coastal blue carbon.

While carbon sequestration is an important part of the story, it should not be seen as a way out of reducing emissions.  Emission reduction still needs to happen to improve climate outcomes for Maine.

DEP also will be including data on renewable fuels which have been left out of the equation in the past. This includes GHG emissions that come from wood and wood waste, ethanol and biodiesel, and solid waste (landfills and methane flares). These will be added to the gross emissions total going back to 1990 and included as part of the reduction goals moving forward.

As of the last biennial “Progress toward GHG Reductions Goals” report, Maine has been on track with reducing GHG emissions. The state is headed in the right direction, but it will need to focus efforts to overcome the larger reduction challenges in the next 10-30 years.

Meghan Grabill is a community development officer with the Island Institute, publisher of The Working Waterfront, working on data analytics and translation and focusing on sea level rise. She can be reached at