The evidence is mounting that natural gas has no net climate benefit on any timescale that matters to humanity. In the real world, natural gas is not a “bridge” fuel to a carbon-free economy for two key reasons.
First, natural gas is mostly methane (CH4), a super-potent greenhouse gas, which traps 86 times as much heat as CO2 over a 20-year period. So even small leaks in the natural gas production and delivery system can have a large climate impact — enough to gut the entire benefit of switching from coal-fired power to gas.
Sadly as a comprehensive new Stanford study reconfirms, “America’s natural gas system is leaky.” The news release explains:
A review of more than 200 earlier studies confirms that U.S. emissions of methane are considerably higher than official estimates. Leaks from the nation’s natural gas system are an important part of the problem.
Second, natural gas doesn’t just displace coal — it also displaces carbon-free sources of power such as renewable energy, nuclear power, and energy efficiency. A recent analysis finds that effect has been large enough recently to wipe out almost the entire climate benefit from increasing natural gas use in the utility sector if the leakage rate is only 1.2% (comparable to the EPA’s now discredited new lowball estimate).
In fact, as a major paper we reported on in November found, “The US EPA recently decreased its CH4 emission factors for fossil fuel extraction and processing by 25–30% (for 1990–2011), but we find that CH4 data from across North America instead indicate the need for a larger adjustment of the opposite sign.”
The new study in Science “Methane Leaks from North American Natural Gas Systems” (subs. req’d) is even more problematic for natural gas as a so-called bridge fuel.
Because the study is a consensus paper from a variety of authors and because the data on leakage rates is not high quality, the paper itself does not suggest a revised natural gas (NG) leakage rate. But the Supplementary Materials do. Deep on page 29 is a section titled, “Calculating leakage percentages associated with possible NG leakage,” where the authors explain that they “can put bounds on the possible leakage rates from the NG system.” Their analysis finds:
“… an excess percentage leakage of 1.8% to 5.4% of end use gas. Coupled with the current estimate of 1.8% leakage of end use gas consumed, this generates a high-end estimate of 7.1% gas leakage.”
As an aside, this range is quite similar to that estimated in the much-maligned (but apparently correct) 2012 Cornell study led by Prof. Bob Howarth.
The authors try mightily to defuse this bombshell by immediately arguing that 7.1% leakage is extremely unlikely and pointing out that, according to one 2012 paper (Alvarez et al.) on replacing coal power with gas, “benefits are seen over a 100-year period if leakage is below 7.6%.”
Woo-hoo! By the time you, dear reader, are dead and the climate is destroyed, that new gas plant may be better than that old coal plant. (And yes, to get a net climate benefit from NG, you still must assume that natural gas displaces only coal and nothing else — an assumption with no basis in reality.)
But let’s take a closer look at NG leakage numbers, which I’ll rewrite as 5.4% +/- 1.8%. I asked the lead author, Stanford’s Adam Brandt, if they had calculated whether there was a uniform distribution from 3.6% to 7.1%, or was there in fact a “most likely” estimate. He said the data wasn’t good enough to determine that, but a “uniform distribution is probably not the best guess.”
Given the risks to humanity from climate change — and the vast sums of money being spent (or squandered) on the NG boom — it seems conservative to take the middle of the range, 5.4%. That’s particularly conservative given that 3 separate studies by NOAA found leakage rates just from NG production of 4%, 17%, and 6-12%!
So let’s go back to Alvarez et al. and see what 5.4% leakage means. Here is the key figure from the 2012 study:
Figure: Maximum life-cycle natural gas leak rate as a function of the number of years needed to achieve net climate benefits after switching from coal power to natural gas. The three curves represent: single emissions pulses (dotted lines); the service life of a power plant, 50 years (dashed lines); and a permanent fleet conversion (solid lines).
At a leakage rate of 5.4%, replacing a fleet of of coal plants with NG plants would have no climate benefit for 50 years! That is, replacing coal plants with gas plants would be worse for the climate for nearly 5 decades.
As an aside, a 5.4% leakage rate means that converting a fleet of either cars or trucks to NG would be worse for the climate for 140 years. Brant explained to the NY Times, “Switching from diesel to natural gas, that’s not a good policy from a climate perspective.”
But it’s even worse than that since Alvarez et al. used what are now out-of-date figures for the global warming potential (GWP) of methane. As I reported in October, the IPCC determined that the 100-year GWP of methane is 40% higher that previously estimated. Correcting for the change means that replacing coal plants with gas plants would be worse for the climate for more than 6 decades.
And again, in the real world, NG doesn’t just displace coal, it also displaces nuclear power, renewable energy, and energy efficiency. So it appears quite safe to say that natural gas simply has no net climate benefit whatsoever on any timescale that matters to humanity.
Perhaps it is time to stop squandering tens of billions of dollars — and rendering billions of gallons of water unfit for human consumption — on a fossil fuel source that has no meaningful net climate benefit in the real world and will do considerable harm.
Posts
No comments:
Post a Comment