Natural gas, a fossil fuel composed primarily of methane (CH4), currently supplies over one-fifth of the world’s energy needs. Its extensive use in electricity generation, heating, and industrial processes makes it a major component of the global energy mix. While the combustion of natural gas offers a clear benefit over other traditional fossil fuels, the leakage of unburned gas and the localized effects of its extraction introduce significant environmental liabilities.
Comparing Emissions During Burning
When natural gas is burned to generate power or heat, it produces significantly less carbon dioxide (CO2) compared to coal or oil. In a modern, efficient power plant, the combustion of natural gas releases approximately 50% to 60% less CO2 than a coal-fired plant generating the same amount of electricity. This reduction in carbon emissions is primarily due to the chemical composition of methane, which has a higher ratio of hydrogen to carbon than other fossil fuels.
Beyond carbon dioxide, the combustion of natural gas results in negligible emissions of several pollutants that create smog and acid rain. Specifically, natural gas produces almost no sulfur dioxide (SO2) or particulate matter, which are major contributors to respiratory illness and regional air quality issues when coal is burned. This cleaner burn profile means that the direct emissions from a natural gas smokestack are substantially cleaner than those from coal or heating oil.
The immediate air quality benefit is a central reason why natural gas is often considered a transition fuel in regions moving away from coal. By replacing older, less-regulated coal plants, a shift to natural gas can rapidly decrease the local concentration of harmful airborne contaminants. However, this advantage only applies to the gases released during combustion and does not account for the powerful warming effect of the fuel itself when it escapes unburned into the atmosphere.
The Climate Impact of Methane Leakage
The most substantial climate drawback of natural gas is the unintentional release of its primary component, methane (CH4), throughout the supply chain. These “fugitive emissions” occur during drilling, processing, transmission through pipelines, and storage. Methane is a far more potent greenhouse gas than CO2 because it is highly effective at trapping heat in the atmosphere.
Methane’s potency is quantified using the Global Warming Potential (GWP) metric, which compares its warming effect to CO2 over a specific time frame. Over a 20-year period, methane is estimated to have a GWP of 81 to 86, meaning one ton traps as much heat as 81 to 86 tons of CO2. While methane has a relatively short atmospheric lifespan of about a decade, its powerful near-term warming impact makes leakage a serious concern for climate targets.
The climate advantage of burning natural gas instead of coal is entirely dependent on the methane leakage rate. Studies suggest that if more than about 6% of the extracted methane leaks into the atmosphere before being burned, the climate benefit of switching from coal is lost over a 20-year period. Current estimates for leakage rates vary widely, with some regional measurements showing rates as high as 8% or more, while official inventories place the average lower, around 1.5%. Reducing these fugitive emissions is technically feasible for a significant portion of current releases.
Local Environmental Footprint of Extraction
The physical process of extracting natural gas, particularly through hydraulic fracturing, or “fracking,” creates environmental challenges. Fracking involves injecting millions of gallons of water, sand, and chemicals at high pressure deep underground to fracture rock formations and release the trapped gas. This process places significant demand on local water resources, with a single well operation requiring between 1.5 million and 9.7 million gallons of water.
The massive water requirement can strain supplies in drought-prone regions and impact local ecosystems and agriculture. Furthermore, the fluid that returns to the surface, known as flowback or produced water, is a toxic byproduct. This wastewater contains the injected chemicals along with naturally occurring substances mobilized from the deep earth, such as heavy metals, high concentrations of salt, and radioactive materials like radium.
Managing this wastewater poses a complex disposal challenge, as it can contaminate surface water through spills or impact groundwater if not handled properly. While evidence of direct contamination of shallow drinking water aquifers from the deep fracturing process is limited, leaks from faulty well casings, surface spills, and the disposal of wastewater into deep injection wells remain documented concerns. The injection of large volumes of wastewater into deep geological formations has also been linked to an increase in induced seismic activity in certain areas.