Varun Sivaram

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The Climate Change Limits of U.S. Natural Gas

by Michael Levi
August 20, 2012


The Associated Press reported last week that U.S. greenhouse gas carbon dioxide emissions have dropped to a twenty-year low on the back of abundant natural gas. “The question,” it correctly observed, “is whether the shift is just one bright spot in a big, gloomy [climate change] picture, or a potentially larger trend.”

I’ve argued repeatedly in the past that surging supplies of natural gas are good news for climate change. But there are important limits to what U.S. natural gas can do. This post is going to illustrate those with some simple numbers.

Let’s start with a reference point. In 2009, in advance of the Copenhagen climate summit, the United States pledged to reduce (PDF) its greenhouse gas emissions to 17 percent below 2005 levels by 2020. It also repeatedly emphasized its intention to reduce those emissions to 30 and 42 percent below 2005 levels by 2025 and 2030 respectively.

How far down that road could a shift from coal to gas get the United States?

I’m going to focus on carbon dioxide emissions from energy. The EIA currently projects that U.S. emissions will be 5,429 million metric tons of carbon dioxide (MtCO2) by 2020, assuming that currently pending fuel economy rules for 2017-25 go ahead as planned. 1,787 MtCO2of that total would come from coal; 1,371 would come from natural gas.

That already reflects a gradual substitution of gas for coal. But what would happen if natural gas completely replaced coal? Assume that the emissions from gas are about half those from coal. Then U.S. emissions would drop to 4,536 MtCO2. That’s 24 percent below 2005 levels.

That leads to our first conclusion: substituting natural gas for coal has the theoretical potential to get us to our 2020 carbon goals. But, unless we deploy it with carbon capture and sequestration, it cannot get us to our 2025 or 2030 goals. (The 2025 and 2030 comparisons require a little bit of extra math that I won’t go through here.) One can push this a bit farther, supposing that natural gas completely replaced oil in residential, commercial, and industrial applications. Oil use in those three sectors is projected to generate 462 MtCO2 in 2020; replacing oil with natural gas could in principle reduce those emissions by somewhere around 150 MtCO2. That doesn’t change our bottom-line conclusions.

But we’re not done. These figures are extreme limits that assume spectacular gains in natural gas use. Alas those gains aren’t practical.

Focus on the coal-to-gas shift. I estimated that a complete replacement of coal with natural gas could slice 894 MtCO2 off of U.S. emissions. You need to burn about 18.2 Mcf (thousand cubic feet) of natural gas to generate a ton of greenhouse gas emissions. This implies that completely replacing U.S. coal with natural gas would require roughly 16 trillion cubic feet (Tcf) of additional natural gas. That’s a 60 percent increment to projected natural gas supplies in 2020. Put another way, it’s more than double the amount of natural gas currently used in U.S. power plants.

This is almost certainly not a practical addition to U.S. natural gas production. Perhaps a more reasonable (but still challenging) outer limit would see half of the U.S. coal use currently anticipated for 2020 replaced with natural gas. That would result in U.S. emissions 17 percent below 2005 levels, meeting the strict part of the Copenhagen commitment but leaving a big lift for other shifts to deliver on the follow-on targets.

The bottom line? Natural gas can do a lot to bend the U.S. emissions curve over the coming years. In even the medium run, though, simply moving from coal to gas is not a substitute for broader policy, at least not if the United States wants to realize the sorts of emissions cuts that both Barack Obama and John McCain talked about only four years ago. Best to think of gas as a climate opportunity – to forestall construction of long-lived and highly polluting infrastructure,  to make carbon capture and sequestration cheaper, to balance intermittent renewable sources – rather than as a solution in itself.

Post a Comment 16 Comments

  • Posted by Mordechai Liebling

    It is a bit disingenuous to focus only on carbon as a greenhouse gas. The real problem with natural gas is not carbon but methane. Under current extraction methods there is a highly significant amount of methane released, particularly from fracking. Methane is 100 times more harmful than carbon in terms of global warming for the first 20 years after release. It is in the next 20 years that we are concerned about hitting the tipping point of 2 degrees Celsius of warming. Increased fracking of natural gas will push the climate passed the tipping point

  • Posted by Stephen Davis

    Well-constructed analysis. Admittedly, it’s hard to capture everything and still make a point on the out-year C02 goals. Sadly, we’re failing to reverse engineer from the desired end-state. CCS is still waiting to go BP. (beyond powerpoint) I’m sure you’ve read Amory Lovins. Check out ‘Reinventing Fire’ if you haven’t.

  • Posted by rtddmc

    Your analysis is sound, but incomplete. Natural gas can also be used in other applications, notably transportation. This would lower emissions dramatically. I find the conclusion that climate goals might not be achieved unless government adopts a particular policy amusing considering that the government has had virtually nothing to do with the current natural gas abundance. In fact, just the reverse. DOE has repeatedly “investigated” fracking without finding violations. Limited government funding of R&D into the renewables is sound policy. Central planning of the energy sector is not.

  • Posted by Daniel

    Let’s avoid talking about nuclear energy. One cannot be green and be for the only source of cheap, carbon free and reliable energy at the same time.

    [ML: Not sure I follow. This is a post about natural gas and coal.]

  • Posted by Daniel

    Regarding my previous post … And also about reducing carbon dioxide emission …. Where are you going with coal and gas ? That won’t cut it …

  • Posted by Daniel

    @ ML

    We have what’s called 2 Super Nova fuels. Uranium and thorium. Enough to power the planet for 5 billion years. the sun has power for 4 billion years.

    And we are talking about coal and methane ? Stuff that kill people ?

  • Posted by Daniel

    One more thing. Substituting one poison (coal) for another (methane) deserves no credit and we have cheap and reliable nuclear power for base load electricity.

    Plus you seem to have totally forgotten that by reducing coal, you are taking away sulfur emissions, which makes this planet cooler.

    What is your solution ?

  • Posted by UzUrBrain

    @ML – Now do a similar study for the amount of CO2 that will be generated using the low efficiency OTCG (once through Gas Turbine) gas generators backing up the “Green Dream – Wind Turbines” You will find that wind turbines, combined with the OTGT, only achieve about 5 % reduction in CO2, yet you get to buy both a wind turbine and a gas turbine. Net result electricity costs twice as much, jobs go overseas. How will that cut CO2? All of these great CO2 numbers you speak of are based upon the high efficiency CCTG’s. When you throw wind (or solar) in the mix, the efficiency goes down, to the point that it is actually better from both a cost and CO2 point of view to just use GAS. So you plan on using a CCTG to back up the wind turbine? Yes that can be done but the turbine is not as efficient as you are not getting the benefit of the steam turbine from the waste heat, you end up running the plant at a less than optimal efficiency point, and these systems cost about 50 – 100% more than the cheaper OTGT.

    Like the Daniel said, if you want to reduce CO2 you must use nuclear. Nay other method will not reduce CO2.

  • Posted by Stephen DuVal

    The question is whether reducing beneficial CO2 emissions should be the focus of our energy policy or whether the economic devastation to the US economy caused by OPEC’s monopoly pricing of oil should be the focus.

    The increase in CO2 emissions, that directly benefit agricultural yields, came about because the Greens shut down the nuclear industry in the 70’s and 80’s. If nuclear had continued to grow, the use of coal for electricity generation would be a historical artifact today.

    Having eliminated nuclear as a major energy source, the next Green campaign focused upon coal. The US has an abundant, cheap supply of coal that can last for hundreds of years. Coal has been demonized and the Green lawyers have pretty much stopped the construction of coal power plants. The EPA has passed regulations to finish them off.

    Fracking, that supposedly destroys our water supply, is next on the Green agenda to shut down the US supply of natural gas.

    The US economy is being drained at the rate of about $500 billion per year by OPEC. The Green response is totally irrelevant; substitute natural gas for coal to generate electricity.

    This article, as several comments have pointed out, totally ignores nuclear power. Nuclear power is the substitute for coal for baseload electricity, limiting natural gas to peak demand.

    Windmills, like spotted owls before them, are the public rational for a policy favoring natural gas for electricity production. Windmills require natural gas plants for backup when the wind doesn’t blow. The turbine, running on natural gas, can be sped up and slowed down as the wind varies. This is a very inefficient way to run the turbines and it turns out that less of the dreaded CO2 would be produced if the windmills were turned off and the turbines were run at their most efficient speed. However facts that contradict the Green religion are ignored.

    If the focus of the US energy policy was to break the OPEC cartel and reinvigorate the US economy, then natural gas would be used as a substitute for oil rather than coal. Natural gas converted to methanol would cap the price of oil at about $50 per barrel. Coal, biomass, and waste can also be converted to methanol. Methanol is an excellent fuel, pollutes much less than gasoline, and is biodegradable so spills are not a problem. Recent car models can run on methanol with minor, cheap (<$100) modifications. Methanol, like gasoline is a liquid at ambient temperature and pressure and the existing liquid fuel distribution network can be used with minor modifications.

    So given that we have a transportation fuel alternative with sufficient supply to end the OPEC cartel, with less pollution than gasoline, that is cost competitive at about $50 per barrel of oil, that requires very little modification to automobiles, that requires minor modifications to the distribution network, the question has to be why isn't this alternative being introduced into the economy. Anyone who said EPA regulations would have the correct answer.

    So the next time a Green advocate discusses the advantages of substituting natural gas for coal in the generation of electricity, ask yourself how much of the $500 billion that is siphoned out of the US by OPEC makes it way back to the Green propaganda machine.

  • Posted by Daniel

    @ Duval

    Your comment: The US has an abundant, cheap supply of coal that can last for hundreds of years.

    What about the Supernova fuels like Uranium and Thorium that can supply base load electricity to the planet for the next 5 billion years?

    Oh. Let’s not call ourselves Senior Fellow for Energy and the Environment

  • Posted by Daniel

    Here is a quote for Albert Einstein for all the anti nuclear greens who just don’t get it:

    Nuclear reactions need not bring about the destruction of mankind any more than the discovery of matches

    …Albert Einstein

  • Posted by Matt Kuhns

    Daniel, I would like to politely submit that when one is responsible for five out of eleven comments, one is coming awfully close to trolling through sheer volume alone. You think the only real energy solution is nuclear and have time for no other viewpoint; you made this clear within your first one or two comments and have have not added any further information since. Repeating yourself ad nauseum is perhaps not the best way to win an argument.

    Also, regarding the suggestion that foolish opposition from “greens” is the sole obstacle to a nuclear-powered utopia: 1) “greens” are hardly a monolithic bloc; many environmentalists are receptive to nuclear power as an option worth considering and some (James Lovelock most prominently) have been outright vocal proponents of it; more importantly, perhaps, 2) it’s fantasy to depict the political risk involved in nuclear energy investment as a sole product of “greens,” particularly given recent events; I don’t think you’ll find any solid evidence that a vastly greater portion of the German or Japanese population has suddenly turned into “greens” in any broad sense, or that the existing “green” minorities in either society somehow achieved a quantum leap in their power and influence over the local government’s energy policies.

    You’re nonetheless free to argue all you want that anxiety over the dangers of nuclear energy rests on misconceptions–I happen to believe that this is true to a great extent, myself–but arguing that those anxieties and misconceptions are exclusively the province of “greens” simply undermines your credibility through its obvious inaccuracy.

    Everyone is entitled to his or her own opinion; no one is entitled to his or her own facts.

  • Posted by Mike_Constitution

    What emissions problem?

    U.S. emissions are at a twenty year low without any meddling by our elitist ruling class.

    Anyway, problems are real, perceived, or contrived and CO2 is one of those that is contrived in order to increase the power of government.

  • Posted by Stephen DuVal

    @ Daniel

    I fully support substituting nuclear for coal to generate baseload electricity. I also support substituting electricity for natural gas for heating, and converting natural gas and coal to methanol for use as a transportation fuel.

    Substituting nuclear for coal is not a prerequisite to breaking the OPEC oil cartel. Breaking the OPEC oil cartel is an immediate critical challenge for the US. Focusing on lowering CO2 emissions supports jihadi terrorism.

    Small modular reactors, built in factories, will reduce capital costs by reducing the lead time for new capacity and by allowing a closer match between additional capacity and new demand. Sodium cooled, metal fueled fast neutron reactors are inherently safe and require no human intervention for automatic (based upon the laws of physics rather than control systems and valves) safe shutdown. Recycling nuclear waste, that is actually 96% fuel, eliminates the waste issue.
    Fast neutron reactors use 96% of nuclear “waste” as fuel; they also use 87% of uranium ore, currently discarded after enrichment, as fuel. Pyroprocessing reduces the cost of recycling and never converts fissile material into a form suitable for proliferation. This is the sustainable clean safe energy source that can provide everyone on this planet with US levels of energy consumption for at least hundreds of years.

    This is not a research project. It has already been demonstrated for 30 years by the EBR II reactor at the Idaho National Lab and by the Integral Fast Reactor program in the 1980’s. GE produced a reactor design S-PRISM based upon these principles in the 90’s. Since 1980 Republican administrations have tried to implement these reactors and Democratic administrations have successfully shut them down.

    Coincidentally, nuclear will reduce/eliminate CO2 emissions.

  • Posted by Ted Glick

    Michael Levi’s first sentence is wrong, significantly. The AP story did not say that “greenhouse gas emissions” are down. It said that “CO2” is down. There are other ghg’s besides CO2, especially methane, which is primarily what natural gas is composed of and which is 72-105 times as powerful a climate forcing element as CO2 over the first 20 years after it is emitted unburned into the atmosphere. When those methane, and other ghg, emissions are factored in, ghg’s have almost certainly increased over the last half-decade, primarily because of the spread of hydraulic fracturing for gas and the major amounts of methane released into the atmosphere by it that process.

  • Posted by Purgatus

    I think the point is being missed here, badly.

    Mr. Levi is pointing out that, even in a “best case” scenario for gas use and expansion, we will still not be able to meet medium-term ghg reduction goals (but may be able to meet short term ones).

    This begs the question, what then?

    Obviously there are a variety of proposed solutions, including nuclear, but the point is that right now there is so much broo-hah-hah about the nat-gas renaissance that no one seems to be taking any serious steps designed to hit those medium term goals.

    The problem is, of course, that any plans (including an expansion of nuclear) which would see us hit those medium term goals a decade and a half from now, have to be started *now.*

    Given our current political climate, I say smart money is with geo-engineering because frankly I don’t see any other way off of this merry-go-round.

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