Rhode Island Greenhouse Gas Inventory

A greenhouse gas (GHG) is any gas that can trap heat from Earth’s surface and reradiate it back down to Earth’s surface. Water vapor is the most the most prevalent GHG, while carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) are the most common anthropogenic (human influenced) GHGs.

A greenhouse gas inventory is a historical account of the quantity of GHGs emitted to, or removed from, the atmosphere over a specific period (e.g., one year) from all sectors of the economy. GHG inventories are used to track progress with strategies implemented to mitigate climate change. 

The Act on Climate was signed into law by Governor McKee in 2021, which requires mandatory, enforceable, greenhouse gas emissions reduction mandates in 2020, 2030, 2040, and net-zero emissions by 2050. The annual GHGI is the primary scientific tool used by the Rhode Island Executive Climate Change Coordinating Council (EC4) to assess the state’s progress towards the Act.

The 2022 Rhode Island Climate Update defined net-zero emissions for purposes of the state’s compliance with the Act on Climate:

‘Net-Zero’ refers to the requirement that the summary measure of greenhouse gas emissions emitted over the course of a calendar year less the summary measure of greenhouse gas emissions absorbed or otherwise broken down over the course of a calendar year equals zero.

The GHGI is updated annually. Since Federal and State government datasets require time to collect, GHGIs typically lag 2+ years behind the current year. DEM is working to shorten this delay to provide policymakers the most up-to-date information to assess the state’s progress towards the Act on Climate.

The GHGI details economy-wide sources and sinks of emissions back to 1990, which is the “baseline” year identified by the Act on Climate. Methodologies are kept relatively consistent across the timeseries to maintain an accurate depiction of how emissions change.

The most common anthropogenic greenhouse gases, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), are estimated. Fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃) are also covered.

Greenhouse gases have unique lifespans and trap heat in the atmosphere with varying intensities. To assess the impacts of all gases on the same scale, emissions are converted to a common unit called million metric tons carbon dioxide equivalent (MMTCO₂e). This unit uses the global warming potential (GWP) metric to reconcile the physical differences GHGs have in the atmosphere over a period of 100 years. The GHGI currently uses the GWP metrics from the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5). 

The GHGI generally follows the greenhouse gas inventory requirements of the United Nations Framework Convention on Climate Change (UNFCCC) and uses the methodologies of the 2006 IPCC Guidelines for National Greenhouse Gas Inventories and its refinements. An exception is made for the energy sector, which includes emissions from electricity consumption in lieu of emissions from electricity generation. 

Energy

• Transportation (aviation, highway vehicles, and non-road sources)
• Electricity Consumption
• Residential Buildings
• Commercial Buildings
• Industrial Buildings
• Natural Gas Distribution

Industrial Processes and Product Use

• Chemical Industry
• Mineral Industry
• Metal Industry
• Electronics Industry
• Product Use

Agriculture

• Livestock
• Soil Management

Waste

• Solid Waste Disposal
• Wastewater Treatment and Discharge

Natural and Working Lands

• Forest Land
• Cropland
• Grassland
• Wetlands
• Settlements 

Before emissions can be estimated, “activity data” needs to be collected by the Federal government or State agencies. Examples of activity data are number of registered vehicles, amount of natural gas consumed by homes, or the population of livestock in the state. Activity data is multiplied by a unique “emissions factor” – developed by the IPCC, the Federal government, or DEM – to estimate the emissions from each source. For example, the emissions factor for natural gas is 31.87 lbs CO₂/MMBtu. Once emissions are determined for each sector, they are summed to obtain the state’s total emissions. 

Electricity consumption is the only sector to include emissions from outside of Rhode Island’s geographic borders. This deviation from international reporting requirements was endorsed by the EC4 on May 11, 2016 to include the effects of Rhode Island’s Renewable Energy Standard (R.I. General Laws § 39-26-4). Renewable energy certificates (RECs) that are settled in Rhode Island offset a portion of the state’s electric load. The remainder of the state’s electric load that is not offset by RECs are covered by power plants operating on the ISO New England electric grid. Click here to learn more about the differences between electricity consumption versus. electricity generation.