NGA ISSUE BRIEF: Natural Gas & the Environment

Natural gas is a key part of the U.S. energy system, representing 32% of energy consumed in 2021. It is a lower-carbon fuel than other fossil fuels, such as oil or coal, and has helped the U.S. achieve environmental progress in recent decades. However, as a fossil fuel, natural gas does contribute to carbon and methane emissions. The natural gas sector is working to lower its carbon output and be part of the needed solution to environmental challenges facing the U.S. and the globe. A review of some environmental trends regarding natural gas is provided in this summary.

Components of Natural Gas

Natural gas is composed primarily of methane. As described by U.S. EPA: "Natural gas is a fossil fuel formed when layers of buried plants and animals are exposed to intense heat and pressure over thousands of years. The energy that the plants and animals originally obtained from the sun is stored in the form of carbon in natural gas."

Natural gas has far fewer emissions of sulfur, nitrogen and carbon than other fossil fuels such as coal and oil. For instance, compared to coal, natural gas produces half as much carbon dioxide, less than a third as much nitrogen oxides, and virtually no sulfur oxides at the power plant.

Natural Gas and Power Generation

Natural gas has been the dominant fuel for new power generation in the Northeast for the last two decades, and one of the leading reasons has been its beneficial impact on air emissions. The U.S. EPA has noted that, "because of their relatively high efficiency and reliance on natural gas as the primary fuel, gas turbines emit substantially less carbon dioxide (CO2) per kilowatt-hour (kWh) generated than any other fossil technology in general commercial use."

Nationally, natural gas became the leading source of power generation, surpassing coal, starting around 2015. As in the Northeast, the rise of natural gas and the decline of more-polluting fuels, such as coal, has led to substantial air improvements; CO2 emissions have fallen by 32% over the last 15 years in the U.S. In June 2021, U.S. EIA noted that almost two-thirds of the decline in CO2 power sector emissions nationally between 2005 and 2019 is attributable to the shift from coal-fired to natural gas-fired electricity generation.

The electric utility sector in the Northeast has achieved major reductions in several air emission areas over the last 20 years-in great part thanks to new, more efficient power sources, from natural gas to renewables.

For example, in New York State over the last 20+ years, NY ISO reports that emissions rates from the power sector dropped by 42% for CO2, and substantially as well for NOx, and SO2. ISO-NE reports that since 2001, total emissions from power plants in New England have dropped by 99% for sulfur dioxide (SO2), 80% for nitrogen oxides (NOx), and 41% for CO2. PJM reports that over the last 17 years, between 2005 and 2022, CO2 emission rates fell 37% across its footprint, while nitrogen oxides declined by 87% and sulfur dioxide by 95%.

The chart below shows changes in carbon emissions by the electric power industry in the region, for the years 1990, 2000 and 2021, as an example of the progress that has been made in the region in reducing emissions.

Comparison of Air Pollution
from Fossil Fuels

(average emission rates measured in pounds for air pollutants produced per megawatt hour of electricity generated, U.S.)

  SO2 NOx CO2
Natural Gas 0.1 1.7 1,135
Oil 12 4 1,672
Coal 13 6 2,249
Source: U.S. EPA

The U.S. Department of Energy notes: "Whether produced via conventional or renewable methods, the advantages of natural gas as an alternative fuel include its domestic availability, established distribution network, relatively low cost, and emissions benefits." NGVs operate on compressed or liquefied natural gas; and hydrogen is another potential option.

Natural Gas Vehicles (NGVs)

The natural gas vehicle (NGV), also known as CNG vehicles (for compressed natural gas), has many environmental advantages. NGVs remain a competitive alternative to gasoline or diesel fuels, particularly for certain key markets such as fleets and urban bus systems.
The U.S. Department of Energy's alternative fuel vehicle website notes: "Commercially available medium- and heavy-duty natural gas engines have demonstrated over 90% reductions of carbon monoxide (CO) and particulate matter, and more than 50% reduction in nitrogen oxides (NOx) relative to commercial diesel engines."

According to NGV America, typical dedicated NGVs can reduce exhaust emissions of:
  • Carbon monoxide (CO) by 70%
  • Non-methane organic gas (NMOG) by 87%
  • Nitrogen oxides (NOx) by 87%
  • Carbon dioxide (CO2) by 20 to 30% below those of diesel and gasoline vehicles.

Reducing Methane Emissions within Gas System Operations

The natural gas industry is cognizant of its responsibility to reduce emissions from its system operations.

Many of NGA's distribution and transmission company members already participate in the U.S. EPA's "Natural Gas STAR" Program - progress continues on this front. For 2018 in the U.S., Natural Gas STAR partners reported methane emissions reduction of 130.6 Bcf, providing "cross-cutting benefits" according to EPA. Cumulative reductions nationally since the year 2004 total 1.6 Tcf.

Methane emissions related to U.S. natural gas systems have declined by 15.7% since 1990, according to the EPA's 2021 national GHG inventory report released in April 2023. The report notes: "Natural gas systems were the second largest anthropogenic source category of CH4 emissions in the United States in 2021, accounting for 181.4 MMT CO2 Eq. of CH4 (22.9 percent of total CH4 emissions and 2.9 percent of total gross emissions). Emissions decreased by 33.7 MMT CO2 Eq. (15.7 percent) since 1990 largely due to decreases in emissions from distribution, transmission, and storage." [EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2021, page ES-13]

For the distribution sector, the main emphasis has been on accelerating the replacement of older, more "leak-prone" pipe. EPA's 2021 GHG report (released in April 2023) indicates that methane emissions related to the nation's gas distribution system has declined by 70% since 1990 - reflecting tremendous progress in that sector.

As noted above, accelerated pipeline replacement of "leak-prone" system components, such as cast iron, is an industry and U.S. DOT priority - see separate issue brief at:

The Key Roles of Efficiency and New Technology Innovations

Efficiency remains a resource of immense opportunity for the U.S. and the region. The Northeast states already are national leaders in their per capita energy efficiency, and the utilities in the region, electric and natural gas, have been active for years in efficiency programs.
Over 40% of the total annual national investment in natural gas efficiency programs is made within the nine Northeast states alone (CT, ME, MA, NH, NJ, NY, PA, RI and VT). (Data source: ACEEE, December 2022). These gas efficiency program investments - and energy savings - will continue in coming years.
Look for further information on the NGA's gas efficiency page here:
Another element of focus for natural gas utilities is utilizing new technology innovations to reduce or offset carbon intensity in supply. These include renewable natural gas (RNG) and hydrogen.
RNG, also known as bio-methane or biogas, is pipeline quality gas derived from biomass that is fully interchangeable with natural gas. The natural gas network is seeking to increasingly include renewable gas from dairy farms, waste water treatment plants, landfills, wood waste and food waste plants.
In the Northeast, there is growing interest and initiatives toward incorporating RNG. Look for further information on NGA's RNG page here:
Finally, among the energy sources seen as potentially significant for helping establish a low-carbon energy future is hydrogen. For natural gas systems, hydrogen has the potential to reduce carbon intensity through blending into existing gas pipeline systems. Look for further information on hydrogen's potential here:

Shale Gas Production and the Environment

An environmental issue of interest concerns the development of shale gas resources in the U.S. The MIT study on natural gas from June 2011 notes that "the environmental impacts of shale development are challenging but manageable."

In August 2011, an advisory group to the U.S. Energy Secretary released a series of consensus-based recommendations calling for increased measurement, public disclosure and a commitment to continuous improvement in the development and environmental management of shale gas. The report calls for industry leadership in improving environmental performance, underpinned by strong regulations and rigorous enforcement, evolving to meet the identified challenges.

The Pennsylvania Department of Environmental Protection (DEP) has comprehensive information on its regulatory role regarding shale gas production in that state; it can be found here:

For Further Information

U.S. EPA Natural Gas STAR Program

U.S. Alt Fuels Vehicle Center, Natural Gas Vehicle Emissions

U.S. EPA, Greenhouse Gas Emissions

Pennsylvania DEP 2021 Annual Oil & Gas Report, released 2022

Pennsylvania Dept. of Environmental Protection, Marcellus Shale page