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Carbon Calculation: Natural Gas vs Coal

7 February 2012 Leave a comment

If you follow the media, especially in PA, you’d be led to assume Natual Gas is the energy source of the future. That may very well be so, at least the near future. Many have proffered that we are in the “Natural Gas Century”, though how long this “Century” lasts may be up for some debate. Natural gas does indeed provide cleaner combustion than coal (38%) and oil (32%), but how much difference do these improvements make in the long run? Or asked another way, how long will using alternative fossil fuels delay crossing certain thresholds?

Mauna Loa CO2 Measured data (red), extrapolated to 2050

The atmospheric CO2 dataset collected from atop Mauna Loa Observatory suggests that we will cross the 450ppm threshold in early 2037, if we maintain our current energy portfolio. This little experiment calculates the change in atmospheric CO2 if we were to alter the energy portfolio by replacing coal with natural gas. To do this, I create 3 scenarios increasing natural gas use by 50%, 100%, and 200%.  There are a few basic assumptions in this calculation. 1) Natural Gas will only be used to  replace the dirtiest fuels: coal first, then oil. 2) The current energy portfolio is the same energy portfolio that’s been used for the last 50 years, and is responsible for the measured increase in CO2. 3) The change from our energy portfolio will happen instantaneously at 2025. There may be additional benefits achieved from ramping up to these goals, but substantial change takes time, here approximated as a 13 year implementation plan. 4) 450 ppm atmospheric CO2 is a threshold that is desirable to avoid. Many have suggested that 450 ppm will equate to ~2C degree warming.  450 will serve as the threshold for evaluating the different scenarios.

https://thevandegraph.files.wordpress.com/2012/01/energy-panel.jpg?w=1024

Scenario 1 increases our current natural gas use by 50%, moving from the current 25% to 37%. If implemented in the year 2025, this will delay us crossing the 450ppm threshold by 15 months.  Scenario 2 increases natural gas use by 100%, making it responsible for 50% of all energy. This would reduce our CO2 emissions enough to offset the threshold by 2 1/2 years.  In the maximum 200% increase scenario, the threshold is delayed by 5 years.

While at first this delay of only a few years seems insignificant, it would represent a substantial change in energy tastes and/or policy, which we have only seen in a limited expanses. Additionally, even the minimum scenario 1 calculation shows that the threshold is delayed by more than a year, after only 12 years of implementation.  That equates to an 8% delay. These carbon savings would continue to accumulate and have larger impacts over longer time horizons.

There are a few caveats, however. 1) This calculation assumes that natural gas will directly compete with only the dirtiest coal and oil, when in fact it will compete with all energy sources.  2) Natural gas is still a fossil fuel and does not get around the fundamental limitation of fossil fuels, which is that they are finite. 3) Natural gas production has the potential for direct release of methane, which is a 12x more efficient greenhouse gas than CO2, though it has a much shorter residence time (~10-12 years). While natural gas will not be the end-all energy savior, the interest in it does represent a first step away from coal and oil and does have the potential to buy us more time while we work toward a more comprehensive solution to our energy concerns. While increased natural gas use  provides a rather minimal change,  it is a change nonetheless, and showing that we can change our energy use will help ease the fears associated with the massive energy overhaul that will be required to fuel our future.

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Categories: Climate, Energy Tags: , , ,