Rhodium’s National Energy Modeling System (RHG-NEMS)

Production and use of energy are the leading contributors to US greenhouse gas (GHG) emissions, and any meaningful attempt to decarbonize must contend with these emissions. At the same time, supply and consumption of energy and related products are parts of a complex set of interconnected systems, so it’s often critical to apply a system-wide lens when considering emissions reduction approaches.

RHG-NEMS is an economy-wide energy system model that estimates energy production and consumption along with resulting GHG emissions, allowing us to quantify the impacts of changes to the energy system. The model also estimates non-energy-related emissions, full accounting for all six categories of GHGs covered under the Kyoto protocol, and state-level results for key metrics.

Our approach

We develop RHG-NEMS by starting with the National Energy Modeling System (NEMS), a model developed by the US Energy Information Administration to produce their Annual Energy Outlook. NEMS is an economy-wide energy model that finds an optimal, lowest-cost solution to balance energy supply and demand subject to physical, economic, and policy constraints. NEMS features technology-rich representation of energy production, conversion, and consumption, allowing for in-depth projections of the energy system and associated GHG emissions under current and prospective policies.

We develop and implement our own projections for clean energy cost and performance characteristics by regularly reviewing data from National Labs, academic literature, and industry assessments. We also expand representation to a wider range of decarbonization technologies including emerging clean technologies like direct air capture and sustainable aviation fuels. We also integrate Rhodium Group’s Industrial Carbon Abatement Platform (RHG-ICAP) to model deployment of point-source carbon capture and clean hydrogen production and use in industry.

RHG-NEMS produces emissions estimates that are consistent with the Environmental Protection Agency’s annual Inventory of Greenhouse Gas Emissions and Sinks, allowing for comparison of emissions outcomes with historical baselines. To do so, we expand RHG-NEMS beyond energy system CO₂ outcomes to incorporate a full range of GHG emissions including methane and nitrous oxide as well as projections for land use, land-use change, and forestry.

We also downscale emissions to all fifty states plus the District of Columbia, Puerto Rico, Guam, and other US territories. Because of this geographically granularity, we are able to incorporate a wider range of state policy actions.

Policy-relevant analysis

Rhodium Group uses modeling from RHG-NEMS to provide timely, relevant analysis for decision-makers and stakeholders in the policymaking process. Each year, we release Taking Stock, our projections of US GHG emissions under current federal and state policy, to provide a baseline against which to assess additional potential policy action.

We also use RHG-NEMS to quantify policy impact at different stages. We provided early estimates of the impacts of the Inflation Reduction Act and joined other modeling teams to contribute an article to the journal Science discussing those results. We also use our analysis to inform ongoing conversations about policy, including during design and implementation. The model is also useful in quantifying the potential emissions implications of policy repeals and rollbacks. Results from RHG-NEMS can also help shape the policy agenda, identifying future emissions sources that require policy attention and suites of policies than can address those emissions.

Explore detailed results

We provide national and state-level results for much of our work on ClimateDeck, our free data delivery and visualization platform.