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Is “Natural” Gas Clean?

Several years ago, natural gas was identified as a bridge fuel that would enable Vermont (and the U.S) to reduce its carbon foot print during our transition away from fossil fuels. At the time, it seemed as the perfect solution that would buy Vermont, the United States and even the world the time we needed to avoid a future global genocide that will most certainly occur if the earth’s temperature continues to rise unchecked. Both the Vermont and the United States as a whole started down the road towards replacing the “dirty” fossil fuels with Natural Gas, especially as a result of the seemly endless supply, as gas has been made available through the process of hydrofracturing or “fracking”.


Natural Gas is a bridge to nowhere!

Unfortunately, it would seem that once again, anything that seems too good to be true, is not. Natural Gas has quickly become recognized as the “Bridge to Nowhere”. Not only is fracking devastating to the land, using and polluting large quantities of water, triggering an endless number of earthquakes and causing health issues for those who are unfortunate to live nearby, it is a major source of methane leaks. The current method of extracting and transporting the gas, not to mention the abandoned wells, leak methane[1]. According to the United Nation’s Intergovernmental Panel on Climate Change (IPCC), Methane is 86 times more potent as a greenhouse gas than Carbon Dioxide over a 20 year timeframe and is a major contributor to global warming. Since climate change is a global “planet” issue and not just a local Vermont issue, we can no longer just focus on how our energy choices impact us locally, but must also consider the upstream emissions as a result of the extraction process. Even though the “fracking” locations may be hundreds of miles away from us, we are impacted by its global warming impacts in Vermont as is true everywhere else on our planet.

In March 2014, the IPCC issued the final version of their Assessment Report 5 [[2]]. The IPCC AR5 publication broadly comprises three working group specific volumes and a synthesis report summarizing the IPCC AR 5 findings for policy makers. Of special interest is the volume authored by the IPCC Working Group 1 entitled “Climate Change 2013: The Physical Science Basis” [[3]]. Within the IPCC WG1 AR5 volume’s series of chapters, the Chapter 8 “Anthropogenic and Natural Radiative Forcing” describes the underlying physical science research supporting the specification of the most widely applied greenhouse gas emission metrics. As part of this underling science, the IPCC AR5 defined a metric called the “Absolute Global Warming Potential” for various fossil fuels. In the case of Natural Gas, the Global Warming Potential (GWP) is a ratio of two greenhouse gas emission metrics, the Methane Absolute Global Warming Potential (AGWPCH4) and the Carbon Dioxide Absolute Global Warming Potential (AGWPCO2).

To illustrate the point, I have included the Figure 8.29 reproduced below from the IPCC WG1-AR5 (chapter 8, page 712). The two AGWP graphs in the figure are an approximation of the multi-decade cumulative atmospheric warming caused by two representative greenhouse gas emissions sources. One of the sources emits a single pulse of Methane (CH4). and the other source emits a single pulse of Carbon Dioxide (CO2). The two emission sources each release the same gas mass as their peer (I. e. 1 Kilogram pulse emission of Methane and 1 Kilogram pulse emission of CO2).


Looking at the Figure 8-29 graph, we see that both of the AGWP quantities are not fixed numbers. The yellow AGWPCH4 curve initially rises exponentially for five decades and it then transitions to a steady-state plateau. This plateau occurs because once the Methane pulse emission has been removed from the atmosphere by decay processes then it no longer contributes to atmospheric warming. Meanwhile, the long-lived CO2 pulse emission slowly accumulates its contribution to warming of the atmosphere and the blue AGWPCO2 line increases linearly with the time horizon. Eventually the CO2 emission’s cumulative climate warming impact exceeds the impact of the Methane emission. The ratio between these AGWP is the Methane GWP metric, shown in the Figure 8-29 as the curve labeled GWPCH4. The GWP metric decays exponentially over a span of centuries.

When Natural Gas is used to heat our homes and businesses, each year more and more Methane emissions leak into the atmosphere as the gas is extracted, processed and transported to each home, as shown by the red arrows in the diagram below. It is the accumulative impact of this Methane that is the major issue when it comes to global warming. The illustration to the left has been included to demonstrate this concept.


Each “red arrow” represents a Methane “Sustained Emissions Pulse” with a half-life of 20 about years. Likewise, CO2 emissions are released as the fuel is burned. These emissions are depicted by the blue arrows or “Sustained Emission Pulses” in the diagram below. Though the carbon dioxide stays in the atmosphere much longer (i.e., hundreds of years) than the methane, the methane has a much greater impact during the first 20 years of it being released.   This is illustrated by the thickness of the arrows. To account for the total Absolute Global Warming Potential of using the natural gas over a period of time, the values associated with each pulse are summed together.

As shown in the highlighted area above, the total Absolute Global Warming Potential, up through a specific year (in this case year 3), is a summation of the climate warming energy for each individual year for each “pulse”.

Using the Absolute Global warming Potential formulas provided in the IPCC report, it is possible to compute the cumulative climate warming energy impact for a specified amount of energy using different fuel types. The graph below, shows the global warming potential of number 2 fuel oil compared to natural gas, assuming the methane leakage rate identified by ANR[4]. We have also included the global warming impact of using a cold climate heat pump to generate the same amount of “heating” energy.

The results of the Absolute Global Warming Potential analysis on a hypothetical Vermont residential heating market are shown below in below.


In this comparison of three types of home heating systems, the cumulative climate warming energy caused by heating 480 residences is evaluated over a 100 year period. All 480 residences are assumed to have the same 100 Million BTU annual heat load. The 480 residences are divided into three groups of 160 households each. Each group of 160 households operates a different type of heating system:

    • #2 heating fuel oil fired boiler, having an 80% efficiency
    • gas-fired boiler, having an 80% efficiency
    • Cold Climate Heat Pump (CCHP) with a heating oil-fired boiler as its back up heating system. The CCHP has a winter season Coefficient of Processing of 2.8. The CCHP carries 90% of the annual heat load and the backup boiler unit handles the remainder.


For the CCHP heating system, the above illustration assumes that the associated greenhouse gas emissions would occur at one or more electrical generation facilities within the ISO New England [[5]] power grid pool. About 50% of the annual power generation is zero emission: nuclear, hydroelectric, and utility scale renewable energy. The gas-fired power plants generate a 45% share of the annual ISO-NE power. Coal and oil power plants are the remaining 5% and many of them are poised for replacement by gas-fired power plants. The ISO-NE forward looking capacity statements [[6]] anticipate that for the foreseeable (10 year) future the gas-fired power plants will continue to expand their dominance of the ISO-NE electric power generation fleet. The forward capacity interconnect queue has 4,500 Megawatts of gas-fired power generation proposed out of the 8,300 Megawatts [[7]] in the queue. Given these ISO-NE forecasts, about 50% of the future CCHP electrical power will come from gas-fired power plants and the other 50% will come from zero-emission sources.

Consequently, only 0.331 MM-BTU of gas energy is needed to generate the electricity for the heat pump to deliver 1 MM-BTU of residential heat. Referring back to the graph on page 3, we see the CCHP greenhouse gas emissions incur dramatically smaller amounts of cumulative climate warming energy versus both the gas-fired boiler and the heating oil-fired boiler households.
The graph clearly shows that Natural Gas is not “cleaner” than number 2 fuel oil for the first 35 or more years of it being burned when one considers the upstream methane leakage. The good news, though, is that electric cold climate heat pumps have a much lower Absolute Global Warming Impact than either fuel source! The use of natural gas will actually have an increased negative impact on global warming over number 2 fuel oil. The only way to reduce our GHG emissions is to migrate away from heating our homes, businesses, and schools with fossil fuels not substituting one for another.


[1]     In a recent Docket 8180 filing, the State of Vermont Agency of Natural Resources (“ANR”) nominated an upstream Methane leakage emissions estimate of 0.54 Kilograms of Methane leaked per MM-BTU of gas energy consumed. (State of Vermont Agency of Natural Resources, Department of Environmental Conservation, Air Quality Climate Division, pre-filed testimony of Mr. Merrell, page 10 starting at line 10 to page 12 line 22; June 13th 2014.)


[3]     IPCC Working Group 1, Assessment Report 5, Climate Change 2013: The Physical Science Basis,

[4] Methane Leakage Rate of “0.54 kilograms per MM-BTU”

[5]     Independent System Operators New England 2014 Regional Electricity Outlook, January 2014,

[6]     Independent System Operators New England Regional System Plan, November 6th 2014,

[7]     Utility scale wind is the other major power source occupying the queue

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