A letter in Climatic Change looking at the life-cycle greenhouse warming potential of natural gas raised a lot of hackles a little while back. If, as the authors posit, replacing coal and oil combustion with gas-fired turbines could actually accelerate global warming rather than slow it down, then we have a serious problem, given the investments being made in gas.
Much the skepticism about that study could be traced to the background of the lead author, Robert Howarth, who happens to have a history of opposing gas fracking. Of course, Howarth's scientific credentials, or his activism, have no real bearing on the math that produces some very daunting numbers about the practical impact of drilling for gas and burning it. But it is unavoidable that any scientist who dallies even tangentially with political activism will run into problems convincing skeptics that he or she hasn't got some ulterior motive. So what this debate needed is an unimpeachable scientific authority to weigh in.
Enter Tom Wigley, senior research associate at the National Center for Atmospheric Research (NCAR), and a fellow of the American Association for the Advancement of Science. He's got a letter coming out in the same journal, Climatic Change, that reaches similar conclusions, although his research involves different approaches.
The basic idea is this: because burning coal releases lots of aerosols that hang about the atmosphere reflecting sunlight, a significant portion of the warming effect of the practice is masked by a cooling effect. If we stop burning coal in favor of technologies that don't involve aerosols, we lose that cooling effect. So, unless the alternative has a really, really low warming effect (something close to zero), we won't be accomplishing much.
The product of combustion of natural gas has only about half the global warming potential of coal's. If you take that into account, you find that
... a worldwide, partial shift from coal to natural gas would slightly accelerate climate change through at least 2050, even if no methane leaked from natural gas operations, and through as late as 2140 if there were substantial leaks. After that, the greater reliance on natural gas would begin to slow down the increase in global average temperature, but only by a few tenths of a degree.
That's from the NCAR press release. You can read the whole, relatively accessible paper. Here's the abstract:
Carbon dioxide (CO2) emissions from fossil fuel combustion may be reduced by using natural gas rather than coal to produce energy. Gas produces approximately half the amount of CO2 per unit of primary energy compared with coal. Here we consider a scenario where a fraction of coal usage is replaced by natural gas (i.e., methane, CH4) over a given time period, and where a percentage of the gas production is assumed to leak into the atmosphere. The additional CH4 from leakage adds to the radiative forcing of the climate system, offsetting the reduction in CO2 forcing that accompanies the transition from coal to gas. We also consider the effects of: methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced CO2 emissions. When gas replaces coal there is additional warming out to 2050 with an assumed leakage rate of 0%, and out to 2140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small.
The interesting thing is that even without factoring in what are known as fugitive emissions, which is the subject of of Howarth's study, natural gas doesn't come out ahead. Natural gas is mostly methane, which has a much larger global warming potential than carbon dioxide. If you assume some leakage -- most estimates are between 2 and 10% -- things get worse. Here's Wigley's take-home-message graph, with avoided warming on the y axis:
So switching to natural gas accomplishes zero in the best-case, fantasy scenario (in which Howarth is totally wrong), until the mid-point of this century at the earliest. Given the need to get our emissions down way below current levels long before 2050 if we want to avoid serious problems adapting to the new climate, this would suggest that natural gas isn't even a useful bridge technology, as many have argued, but a complete non-starter. T. Boone Pickens, take note.
This line of thinking isn't just an indictment of just natural gas, but of all alternatives that aren't effectively zero-emissions. If getting off of coal (and oil to a similar but lesser degree) means we lose a significant cooling effect, then whatever new technologies we choose have to be squeaky clean, not just marginal improvements. Carbon capture and sequestration, for example, will have to function at near-perfect efficiencies of more than 90%, which is a bit higher than what some researchers say is realistic.
The same logic applies to any modest emissions-reduction strategy. If, as seems to be case, we only have a few decades to get with the program, then we don't have the luxury of time or physics to ease ourselves off fossil fuels. We have to go cold turkey.
--
Wigley, T. (2011). Coal to gas: the influence of methane leakage Climatic Change DOI: 10.1007/s10584-011-0217-3
- Log in to post comments
Bear with me please, long post.
"Of course, Howarth's scientific credentials, or his activism, have no real bearing on the math that produces some very daunting numbers about the practical impact of drilling for gas and burning it."
Well, first of all, his scientific credentials in life-cycle analyses (LCA) of natural gas production and transmission has significant bearing on his estimates. Fact is, he has no credentials. He's an ecologist. When a climate skeptic with a PhD in an unrelated field steps into climate science to utter some nonsense, climate scientists (quite rightfully) get upset. I don't blame them. I don't like it either.
Now, how does do his credentials manifest themselves? Because his LCA is flawed from top to bottom. Just two examples:
1) He assumes no flaring of shale-gas flowback, something very, very commonplace in industry, not because it reduces the carbon footprint, but because you don't want your rig to blow up if that methane gets in the intakes of your diesel engines.
2) His estimates of gas lost through the pipeline system are probably vastly overstated. For all his arm-waving around lost and unaccounted for gas (which is not nearly the same as leaked gas), he neglects to mention there'd be a big increase in local gas production and local gas consumption, which would reduce the number of leakage points the gas would have to travel through, overall reducing fugitive gas.
If he had any knowledge whatsoever of how this gas is produced and how it's transported, he would not have made these amateur mistakes.
A new and, frankly, far more comprehensive paper on the subject is Jiang et al. (2011). It includes folks experienced in this subject. They use proper risk analyses and Monte Carlo simulations to estimate realistic low and high values. And, guess what? Their conclusion is that the status quo stands: shale gas is little different than conventional gas and it offers significant GHG reductions when compared to coal.
http://iopscience.iop.org/1748-9326/6/3/034014
And, of course, Howarth's paper was "peer reviewed", but, as we know from Spencer and Braswell (2011), crap that shouldn't get published gets published all the time. Very few analysts in the field of energy systems are taking the Howarth publication seriously.
All that being said, Wigley's approach seems very, very interesting, with a new way to look at the subject, and I'd be keen to see a copy of the paper.
This is really surprising to me. I thought the cooling effect by aerosols from coal burning was on a very short term, in the order of a few years at most. I would also mean that it's a bad idea to burn coal as 'clean' as possible (without generating aerosols).
Also, the analysis is one-dimensional if it just focuses on temperature. I don't think a climate with no carbon emissions is the same as one with plus additional aerosols, even if they perfectly cancel each other out in forcings.
Quoting some communication-fail of mine: "He assumes no flaring of shale-gas flowback, something very, very commonplace in industry"
He assumes no flaring of shale-gas flowback, but flaring is very, very commonplace in industry.
The factor of two reductions assumes a steam only plant, i.e. the gas is used to boil water at about a 35% efficiency fossil fuel to electricity. However the combined cycle plants run at 60% plus efficiency, by running the gas thru a gas turbine (at a higher temp so you get better Carnot cycle efficiency). Then you use the waste heat to boil water and run a steam turbine as well. So you get close to 2x better efficiency in terms of electric output per unit of potential heat from the fuel. Then add the reduction in CO2 per unit of heat from methane over coal and its at least 4x. Also it is likely that the energy cost of moving gas to the plant is less than coal as well as the energy cost of extraction as well.
I don't think a climate with no carbon emissions is the same as one with plus additional aerosols, even if they perfectly cancel each other out in forcings.
Been through the Wigley paper. Interesting. But I question using the CCSP2 no-policy scenario as his base case from which to ultimately determine temperature change.
Primary energy from coal in his base case would quadruple by 2110 and the primary energy from gas in in his base case would nearly triple over the same time period. Then, when he does his fuel switching, gas primary energy quadruples by 2110 and coal primary energy only doubles.
Absolutely, if we're still burning fossil fuels at that rate for that duration of time, we're going to have some major problems. No doubt in this world. If we're not off these fuels before 2050 for the most part or have complete CCS in place by then, we're in trouble.
BUT: fuel switching won't occur in a policy vacuum where it's only about switching fuels. Fuel switching will come in a policy setting where some coal would be replaced gas and other coal would be replaced by alternative, low-emissions sources of energy. Overall, gas burning won't go up nearly so dramatically as he has in this paper.
I'd also like to point out that his natural gas lower emissions scenarios (2.5% or less) can easily be achieved with simple, enforced regulations on gas production and transmission, including mandatory green completions (capture of all gas and no flaring) and retrofitting of older pipelines to ensure lower fugitive emissions.
Finally, I think this methodology has some merit, though I'd like to see some "policy" scenarios that include coal being switched out with other forms of energy, like hydro, solar, and wind.
Where is douche boy?? Probably relocating to higher ground in response to all the apocalyptic plant food floating Around ata few ppm. What a douche.
HELLO!!!!!!!!!!!!!!!!!!!!!!!!
DOUCHEBOY!!!! WHERE you BE????
We need your superhero cape wearin' @zz to save us from 3 ppm of plant food CATASTROPHE!!!!!!
seriously. douchey douche!! come save us!!! we countin on you and stuff.
What if we just gave the earth a GIANT DOUCHE!!!! Would that clean things out good enought for you douche boy? I mean James?
That would be more scientific than the carbon crap you're trying to peddle.
Go algore!!! Go algore!!! Go algore!!!!!
Gosh, no wonder the denialists aren't getting anywhere with rhetoric like that.
Plant food? Are the plants on a diet, then? 'cos that "plant food" is accumulating like nobody's business.
Obviously either the plants are consorting to kill off all the animals by going on "hunger strike" or the denialists are completely unaware of what plants actually do.
How in the hell can one idiots opinion effect an entire industry. Guys like this have only one real interest. To get published. Then you know what your talking about. You've been published. WOW. That must mean your a genius. What a maroon...