NGA ISSUE BRIEF: Natural Gas & the Environment

  • Natural gas is the cleanest of the fossil fuels, with substantially lower emissions of nitrous oxide, sulfur dioxide, and carbon dioxide.
  • With its positive environmental profile, gas has been the "fuel of choice" for power generation in the Northeast.
  • Natural gas can also play a positive role in reducing transportation and building sector emissions.
  • The natural gas industry is striving to reduce its environmental impacts, through such cooperative efforts as the U.S. EPA's "Natural Gas STAR" program.
  • Natural gas production-including shale gas development-can be conducted in an environmentally sensitive manner, and yield environmental benefits to society.
  • Methane emissions have declined in the U.S. over the last 2 decades, thanks to industry efforts and line replacements to repair leaks. Reducing methane emissions going forward is a common government and industry goal.

Natural gas is a low carbon fuel, and is seen as a key element in U.S. efforts to transform its energy system to be more efficient and environmentally positive. Natural gas has been the "fuel of choice" for power generation in the Northeast for the last decade in large part because of its positive impacts on air quality and the environment; and it is also seen as a positive environmental fuel for transportation and other sectors. A review of some environmental trends regarding natural gas is provided in this summary.

Environmental Advantages 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 and nationally for over a decade, 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."

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, from 2000 to 2016, NY ISO reports that emissions rates from the power sector dropped by 43% for CO2, 87% for NOx, and 98% for SO2. ISO-NE reports that from 2001 to 2015, total emissions from power plants in New England dropped by 95% for sulfur dioxide (SO2), 68% for nitrogen oxides (NOx), and 24% for CO2.

The charts below show changes in power industry emissions for SO2, NOx and CO2, for MA and NY, for the years 1990, 2000 and 2014, as examples of the progress that has been made in the region in reducing emissions associated with the power sector.

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

Compressed natural gas (CNG) vehicles provide environmental benefits, reliability, cost-effectiveness, and are sourced from domestic supplies. ACEEE rated the CNG vehicle as one of the top 10 "greenest vehicles" on the road. And in October 2009, the National Research Council, affiliated with the National Academies of Science, released a report which observed that "compressed natural gas had lower damages than other options, as the technology's operation and fuel produce very few emissions."

MIT's natural gas study of June 2011 stated that using very efficient natural gas powerplants to replace coal-fired plants is "the most cost-effective way of reducing CO2 emissions in the power sector" over the next 25 to 30 years. Natural gas will also play "a central role in integrating more intermittent renewable sources - wind and solar - into the electricity system because they can easily be brought in and out of service as needed."
Continued investments in gas power generation will yield greater efficiencies and help the region meet its Clean Air-and energy-requirements.

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 very 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.

In October 2009, the National Research Council, affiliated with the National Academies of Science, released a report which noted that: "compressed natural gas had lower damages than other options, as the technology's operation and fuel produce very few emissions."

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 2013 in the U.S., Natural Gas STAR partners reported methane emissions reduction of 51 Bcf, providing "cross-cutting benefits" according to EPA.

Methane emissions related to U.S. natural gas systems have declined by 16.3% since 1990, according to the EPA's April 2017 national GHG inventory report. The report notes that "The decrease in CH4 emissions is largely due to a decrease in emissions from transmission, storage and distribution. The decrease in transmission and storage emissions is largely due to reduced compressor station emissions (including emissions form compressors and fugitives). The decrease in distribution emissions is largely attributed to increased use of plastic piping, which has lower emissions than other pipe materials, and station upgrades at metering and regulating (M&R) stations."

For the distribution sector, the main emphasis has been on accelerating the replacement of older, more "leak-prone" pipe. Early in 2015, a national study led by Washington State University reported that direct measurement analysis showed "decreasing emissions from natural gas local distribution systems in the United States." Replacement of older pipe systems and improved leak surveys were among the reasons cited for the industry performance. A Harvard/BU study found higher estimates for methane emissions in the Boston area; while an ICF study for the Commonwealth of Massachusetts found that for the three geographic areas studied in the state, methane emissions fell within the range of 0.6 to 1.1% of all gas received. ICF noted that "the effectiveness of replacing cast iron and unprotected steel with plastic pipe to reduce emissions is clearly demonstrated in this study."

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:

Shale Gas Production and the Environment

Finally, 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." Industry and government regulatory agencies are working to address development in an environmentally safe manner.

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. Increased transparency and a focus on best practices "benefits all parties in shale gas production: regulators will have more complete and accurate information, industry will achieve more efficient operations and the public will see continuous, measurable, improvement in shale gas activities," the report says. The report calls for industry leadership in improving environmental performance, underpinned by strong regulations and rigorous enforcement, evolving to meet the identified challenges. Further information can be found here:

The natural gas production industry has moved to address the issue of disclosure regarding the additives used in the hydraulic fracturing process. One major step was announced in 2011, when the Ground Water Protection Council (GWPC) and the Interstate Oil and Gas Compact Commission (IOGCC), with funding support from the United States Department of Energy (DOE), unveiled a landmark web-based national registry disclosing the chemical additives used in the hydraulic fracturing process on a well-by-well basis. The initiative provides energy companies involved in oil and gas exploration and production a single-source means to publically disclose the chemical additives used in the hydraulic fracturing process. The web site address is:

In June 2015, the Environmental Protection Agency (EPA) released a draft assessment on the potential impacts of hydraulic fracturing activities on drinking water resources in the United States. It found potential risks but no major impacts to date. EPA's review of data sources available to the agency found specific instances where well integrity and waste water management related to hydraulic fracturing activities impacted drinking water resources, but they were small compared to the large number of hydraulically fractured wells across the country. In December 2016, EPA released the final study. It is not conclusive on the extent of impacts but cited some potential impacts - which industry would note is often related to improper casing and handling of surface water. The study concludes that "hydraulic fracturing for oil and gas is a practice that continues to evolve." The study notes that by focusing attention of the situations described in the analysis, "impacts on drinking water resources from activities in the hydraulic fracturing water cycle could be prevented or reduced." The study can be found here:

The Pennsylvania Department of Environmental Protection (DEP) in its 2016 Oil and Gas Annual Report notes that "Although the number of compliance inspections has increased over the past six years, the number of violations observed has been generally decreasing over this same time period." The rate of violations at unconventional wells is about one-third that of that at conventional wells.

DEP also notes in its 2016 Report: "Although there is no evidence that hydraulic fracturing has resulted in a direct impact to a water supply in Pennsylvania, there are cases where related oil and gas activities have adversely affected private water supplies. DEP investigates all stray gas-related complaints and if it is determined that a water supply is adversely affected by oil and gas activities, DEP works with the responsible operator to ensure the water supply is restored or replaced."

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


U.S. Dept. of Energy, Shale Gas Report, August 2011

Pennsylvania DEP 2016 Annual Oil & Gas Report, released 2017

Pennsylvania Dept. of Environmental Protection, Marcellus Shale page