CBO’s Benchmark Projection of Greenhouse Gas Emissions

Greenhouse gases (GHGs) accumulate in the atmosphere when fossil fuels are burned to produce energy; they also accumulate as a result of industrial processes and activities such as deforestation and agriculture. GHGs, which include carbon dioxide, methane, nitrous oxide, and other (mainly fluorinated) gases, vary in their contributions to atmospheric warming: They remain in the atmosphere for different lengths of time and cause different amounts of warming while they are present. So that GHGs can be compared on a common basis, emissions are often measured in carbon dioxide equivalent units (CO2e), or the amount of CO2 that would cause the same amount of warming over a given period (typically a century).

The Congressional Budget Office maintains a 10-year benchmark projection of annual GHG emissions to estimate the effects that certain GHG emissions policies, such as setting a price on those emissions, would have on the federal budget. This report presents CBO’s most recent projection of GHG emissions. According to that projection, GHG emissions in the United States, measured in CO2e, decline by about 8 percent from 2025 to 2034. That decline is driven by a projected decrease of 15 percent in energy-related emissions of CO2, partially offset by an increase of 9 percent in other, non-energy-­related emissions.

How CBO Constructs Its Benchmark Projection of Greenhouse Gas Emissions

CBO uses information from the Environmental Protection Agency (EPA) and the Energy Information Administration (EIA) to construct its benchmark projection of GHG emissions. The projection is updated annually, following the release of EPA’s Inventory of U.S. Greenhouse Gas Emissions and Sinks and EIA’s Annual Energy Outlook.1 EPA’s inventory is a detailed accounting of annual emissions, including subtotals by economic sector and type of greenhouse gas. Because of the time required to gather data and produce estimates, EPA’s most recent inventory, released in 2024, reports historical GHG emissions through 2022. EIA’s outlook provides long-term projections of U.S. energy markets, including energy-related emissions of CO2 by economic sector, most recently through 2050.

CBO constructs its GHG emissions benchmark as follows: For CO2 emissions from energy use, CBO applies EIA’s projected emissions growth rates, which are sector specific, to the corresponding emissions totals for the latest year in EPA’s inventory. Because EIA does not provide its projections of non-energy-related GHGs in its outlook, CBO uses its own growth rates, which it developed from EIA’s projection model.2 CBO also maintains a 30-year projection by extrapolating from EIA’s projections beyond 2050.

If future laws or administrative actions that would notably affect emissions were adopted after CBO’s annual update, the agency would revise its benchmark to reflect the expected effects of those changes.

CBO’s Current Benchmark Projection of GHG Emissions

In CBO’s most recent GHG emissions projection, emissions fall from 6,182 million metric tons (MMT) of CO2e in 2025 to 5,681 MMT of CO2e in 2034, an 8 percent decline (see Table 1). Energy-related CO2 emissions account for 71 percent of total GHG emissions in the first year of CBO’s projection, and the decline in total GHG emissions over the projection period is entirely due to decreases in those energy-related CO2 emissions. By 2034, energy-related CO2 emissions are 66 percent of the total.

Emissions of CO2 from the transportation sector, the largest single source of energy-related CO2, decline by 8 percent from 2025 to 2034 in CBO’s projection, as vehicle fuel economy—aided by increasing sales of electric vehicles—continues to rise. Because a growing share of electricity is being generated from renewable energy sources such as solar and wind power, CO2 emissions from the electric power sector are projected to fall by 44 percent over the projection period. By contrast, other energy-related CO2 emissions—from a composite of the industrial, commercial, and residential sectors—increase by 4 percent in CBO’s projection.

CBO also expects emissions of other greenhouse gases, and emissions of CO2 from non-energy uses, to increase over the projection period. Methane emissions—primarily from agriculture and the production of oil and natural gas—increase by 3 percent and constitute 14 percent of total GHG emissions in 2034. In the agency’s projection, emissions of non-energy CO2, nitrous oxide, and fluorinated gases all increase as well—by 8 percent, 10 percent, and 25 percent, respectively—through 2034 and together account for the remaining 20 percent of GHG emissions that CBO projects for that year. As energy-related CO2 emissions decline, the relative contributions of non-­energy CO2 and other GHG emissions all increase by several percentage points over the next decade in CBO’s projection.