On January 5, 2026, the Montana Department of Environmental Quality (DEQ) released its Final Greenhouse Gas (GHG) Assessment Guidance, providing state agencies with direction on how to evaluate climate impacts as part of their environmental review obligations under the Montana Environmental Policy Act (MEPA). The guidance provides state agencies with methods and criteria for assessing GHG emissions during Environmental Assessments (EA) and Environmental Impact Statements (EIS), as mandated by recent legislative reforms.
Held v. State of Montana
The origins of this guidance trace back to the 2024 court case Held v. State of Montana, which was a youth‑led climate lawsuit in which sixteen young plaintiffs sued the State of Montana and multiple state agencies including DEQ. The youths argued that the language of MEPA statute in place at that time, which prevented agencies from considering GHG impacts in environmental reviews, violated their constitutional right to a clean and healthful environment. The court ruled in favor of the plaintiffs and declared these prohibitions unconstitutional because they effectively barred agencies from fully evaluating environmental impacts tied to climate change. This ruling eliminated the prior statutory prohibition, including language dating back to 2011 that had barred agencies from evaluating environmental impacts occurring outside Montana’s borders, and confirmed that agencies may consider climate‑related impacts when conducting MEPA analyses. This decision reshaped the legal landscape governing MEPA analyses by affirming that climate-related impacts are part of the environmental review process.
MEIC v. DEQ
The assessment of GHG impacts as part of MEPA was in court again in 2025 in Montana Environmental Information Center (MEIC) v. Montana DEQ. This case involved a challenge to DEQ’s issuance of a Montana air quality permit for a new natural gas-fired power plant, arguing that the agency failed to adequately analyze its GHG impacts under MEPA. The court determined that DEQ must analyze GHG emissions when the project is expected to have a large amount of GHG emissions, as would be the case with the proposed natural gas-fired power plant. While the court recognized that Held removed the categorical ban on considering climate impacts, it also emphasized that the decision did not require DEQ to analyze GHG emissions for every state action. Instead, agencies retain discretion to determine when such analysis is necessary.
The 2025 Legislature and Senate Bill 221
In response to these court cases, the 2025 Montana Legislature passed Senate Bill 221 (SB221), which reformed MEPA and established clear expectations for GHG consideration in state environmental reviews. SB221 repealed and replaced the 2011 MEPA language that had barred agencies from considering GHG emissions and out‑of‑state environmental impacts, ensuring that climate effects can now be evaluated in MEPA reviews. It also introduced several key requirements:
- Mandatory GHG assessments for all fossil fuel projects.
- Discretionary GHG assessments for other categories of projects.
- A requirement that DEQ develop formal GHG guidance for state agencies, outlining when assessments are needed and what methodologies to use.
SB221 clarified that MEPA evaluations remain informational in nature and cannot be used to regulate or deny permits solely based on GHG emissions. However, it ensured that climate impacts are transparently and consistently disclosed during state decision-making processes.
When a GHG Assessment Can Occur
DEQ developed the formal GHG assessment guidance as directed by SB221 and its resulting changes to MEPA. The new DEQ guidance serves as a technical and procedural roadmap for agencies conducting GHG assessments under MEPA. It clarifies when assessments must occur, how emissions should be quantified, and what analytical tools should be applied. The guidance reinforces that MEPA reviews are intended to inform permitting decisions, not dictate them.
Fossil Fuel Projects
State agencies are required to conduct a GHG assessment for fossil fuel projects. Per the definition of fossil fuel activities from Montana Code Annotated § 75-1-220 as amended by SB221, “fossil fuel activity” means a proposed action that authorizes the mining of coal, drilling for oil or natural gas, production of oil or natural gas, compression of oil or natural gas, or burning of coal, oil, or natural gas to generate energy for electricity. Exclusions from this requirement include activities such as burning biomass for electricity or industrial purposes, transportation-related activities (including rail), or water quality and quantity-related leases, permits, licenses, certificates, or other entitlements for fossil fuel activities.
For fossil fuel-fired power plants or electric generating units, the GHG assessment may include GHG emissions from combustion sources, fugitive emissions, mobile sources, and waste management activities. Combustion sources can include boilers, combustors, process heaters, and engines. Emergency flaring of waste gas activities may also be considered where applicable. Examples of fugitive emissions are natural gas leaks from pipelines, valves, flanges, or other equipment, and methane emissions from coal storage and handling. Mobile sources in the context of a fossil fuel-fired power plant project could include on-site vehicles such as maintenance trucks, coal/ash handling equipment, and material transport vehicles. Emissions from waste management could include wastewater treatment at the project site. For coal mining and oil and gas projects, the assessment could potentially include GHG emissions from combustion sources, fugitive emissions, and mobile sources.
Stationary Combustion Devices
If a proposed action creates direct emissions from stationary combustion devices, then the reviewing agency may consider conducting a GHG emissions assessment. The decision to conduct a GHG assessment for stationary combustion devices would be determined on a case-by-case basis if the impacts are potentially significant. Examples of stationary fuel combustion devices include, but are not limited to:
- Incinerators
- Boilers
- Nonmobile engines
- Turbines
- Industrial heaters
- Industrial furnaces
- Kilns
- Ovens/dryers
- Waste gas flaring
- Thermal oxidizer/vapor combustor unit
Construction and Mobile Engine Operation
If a proposed action involves prolonged or continuous use of GHG‑emitting construction equipment or mobile engines, the reviewing agency may choose to include a GHG emissions assessment in its MEPA review. However, if construction activities are short‑term and the agency determines that the resulting emissions would not have the potential to be significant, a GHG impact analysis may not be necessary.
Examples of GHG emission sources from construction activities include:
- Mobile equipment: Excavators, bulldozers, graders, dump trucks, concrete mixers, cranes, material hauling trucks, and specialized machinery such as tunnel boring machines and pile drivers
- Stationary equipment: Generators, concrete batch plants, asphalt plants, crushing and screening equipment, and heating systems
- Support operations: Compressors and water pumps
Ecological Functions
Ecological functions are the natural interactions and processes that maintain a healthy ecosystem and its ability to provide benefits to humans and organisms. For example, forests and grassland ecosystems perform an important ecological function by regulating the carbon cycle and contributing to the long-term GHG balance in the atmosphere. If the proposed action might impact the Earth’s ecological carbon cycle, such that the public would benefit from information about whether the action could result in the sequestration or release of carbon, then the reviewing agency could consider conducting a GHG assessment for that project.
Focus of a GHG Assessment
MEPA requires agencies to evaluate direct, secondary, and cumulative impacts from a proposed action on Montana’s environment. Under current statutory language in SB221, upstream, downstream, and other indirect activities that occur independently of the proposed action—or would occur regardless of whether it proceeds—are excluded from MEPA review. For GHG assessments, this means that the analysis is limited to proximate, project‑related emissions and their resulting impacts on Montana and does not include broader consequential or lifecycle emissions occurring outside Montana’s jurisdiction or through unrelated activities.
For example, when evaluating a proposed coal‑mining project, the GHG assessment would address only the emissions directly associated with the mining activity. It would not include emissions from the eventual combustion of the coal, which may occur outside Montana and is considered an indirect, downstream impact. While MEPA excludes indirect impacts, agencies can provide a discussion in their GHG assessment that presents a project’s emissions within the broader context of global climate change, acknowledging the cumulative nature and impacts of climate change as well the inherent difficulty of attributing precise local impacts to one source.
MEPA refers to secondary impacts as those that occur at a different location or later time than the action that triggers the effect. Secondary GHG impacts may describe how the project’s emissions contribute to global atmospheric concentrations and subsequently influence Montana-specific climate conditions such as temperature, precipitation, and extreme weather. The secondary impact evaluation would not extend into broader lifecycle or external consequential impacts. Because GHGs are well-mixed in the atmosphere and climate change is driven by the cumulative total of global emissions, it is infeasible to trace specific local outcomes (e.g., a Montana heatwave) back to any single project.
In the context of GHG emissions, cumulative impacts refer to the combined contribution of a proposed action’s GHG emissions with emissions from other past, present, and related future actions to global atmospheric GHG concentrations, and the resulting effects on Montana’s environment. The final guidance refers agencies to multiple data sources to quantify cumulative emissions. These cumulative emissions are then interpreted in terms of how they contribute to broader climate changes affecting Montana’s environment
Looking Ahead
As Montana transitions into this updated MEPA framework, the Final GHG Assessment Guidance gives agencies and the businesses they regulate a clearer path forward. While the new requirements do not change MEPA’s role as an informational process, they do offer a framework for consistent and predictable GHG assessments for state actions. For project proponents, this means clear and defined expectations upfront, a transparent review process, and fewer surprises as agencies incorporate GHG considerations into their environmental analyses. Trinity will continue tracking implementation and helping clients understand what these changes mean for upcoming projects. If you would like to discuss how this guidance affects your Montana projects, reach out via email to Ed Warner or call 720.638.7647.
