The U.S. hailed the recent discovery and development of shale gas, as the primary factor for a cleaner and more secure energy landscape. Natural gas is often thought to be a ‘bridge fuel’ between fossil fuels and renewables, even though it falls into the former category. It is indeed a ‘cleaner’ energy source, especially compared to coal; its carbon dioxide emissions are just 45% of those of coal (Andrews and Jelley, 2013). According to the EPA, natural gas emits one third as much nitrogen oxides as coal. In addition, a lifecycle analysis found that “existing domestic coal power plants produce two and a half times more emissions than that of LNG.” In other word, even the cleanest coal technologies were found to produce 70% more lifecycle emissions than LNG.
Natural gas is one of the cheaper energy sources too. The production level has been hiking with shale gas (see the figure below), and the upward trend is expected to continue in the coming decades. Owing to this abundance, natural gas has become the cheapest source of electrical power in the U.S. market, priced at an average of 6 cents per kilowatt hour, vs 9 cents for coal and hydroelectric and 11 cents for solar. Other advantages include its versatility and easy transport; natural gas can be used for residential and industrial uses, and it can be stored or carried relatively easily using pipelines, tankers and other units.
Nevertheless, there is no light without darkness. One of the primary concerns about natural gas, particularly regarding the unconventional sources, is hydraulic fracturing, also known as fracking. The natural gas extraction method can cause, albeit arguably, serious threats on the environment and human health by triggering seismic instability and contaminating underground water sources. Moreover, some say natural gas is actually as harmful in terms of greenhouse gas emissions as coal, if we consider potential methane leaks. Methane, the main component of natural gas, has “a more potent short-term effect on climate change than carbon dioxide”. The chain of pipelines and equipment required to produce and transport natural gas emits an extensive amount of methane, which dilutes the fuel’s less substantial CO2 emissions.
Perhaps the most important point is that relying on natural gas can be an easy alternative to using more renewables, thereby delaying a transition toward a cleaner energy future. Steven Davis, a professor at UC Irvine, made an interesting comment: “cutting greenhouse gas emissions by burning natural gas is like dieting by eating reduced-fat cookies. It may be better than eating full-fat cookies, but if you really want to lose weight, you probably need to avoid cookies altogether.” If people treat natural gas as a non-fossil fuel, the bridge is likely to become a block.
 Source: New York Times, retrieved from http://www.nytimes.com/2015/08/19/science/methane-leaks-in-natural-gas-supply-chain-far-exceed-estimates-study-says.html?_r=0
 Source: EIA, retrieved from http://www.eia.gov/forecasts/aeo/electricity_generation.cfm
 Image source: Center for Liquified Natural Gas (CLNG)