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Wishful Thinking About Natural Gas
Posted on Jul 28, 2014
By Naomi Oreskes, TomDispatch
This piece first appeared at TomDispatch. Read Tom Engelhardt’s introduction here.
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Like most misleading arguments, this one starts from a kernel of truth.
That truth is basic chemistry: when you burn natural gas, the amount of carbon dioxide (CO2) produced is, other things being equal, much less than when you burn an equivalent amount of coal or oil. It can be as much as 50% less compared with coal, and 20% to 30% less compared with diesel fuel, gasoline, or home heating oil. When it comes to a greenhouse gas (GHG) heading for the atmosphere, that’s a substantial difference. It means that if you replace oil or coal with gas without otherwise increasing your energy usage, you can significantly reduce your short-term carbon footprint.
Replacing coal gives you other benefits as well, such as reducing the sulfate pollution that causes acid rain, particulate emissions that cause lung disease, and mercury that causes brain damage. And if less coal is mined, then occupational death and disease can be reduced in coal miners and the destruction caused by damaging forms of mining, including the removal, in some parts of the country, of entire mountains can be reduced or halted.
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So if someone asks: “Is gas better than oil or coal?” the short answer seems to be yes. And when it comes to complicated issues that have science at their core, often the short answer is the (basically) correct one.
As a historian of science who studies global warming, I’ve often stressed that anthropogenic climate change is a matter of basic physics: CO2 is a greenhouse gas, which means it traps heat in the Earth’s atmosphere. So if you put additional CO2 into that atmosphere, above and beyond what’s naturally there, you have to expect the planet to warm. Basic physics.
And guess what? We’ve added a substantial amount of CO2 to the atmosphere, and the planet has become hotter. We can fuss about the details of natural variability, cloud feedbacks, ocean heat and CO2 uptake, El Niño cycles and the like, but the answer that you get from college-level physics—more CO2 means a hotter planet—has turned out to be correct. The details may affect the timing and mode of climate warming, but they won’t stop it.
In the case of gas, however, the short answer may not be the correct one.
The often-touted decrease in greenhouse gas production applies when natural gas replaces other fuels—particularly coal—in electricity generation. That’s important. Electricity is about 40% of total U.S. energy use. Traditionally, coal has been the dominant fuel used to generate electricity in this country and most of the world. (And no one has any serious plan to live without electricity.) Any measurable GHG reduction in the electricity sector is significant and gains achieved in that sector quickly add up.
But a good deal of the benefit of gas in electricity generation comes from the fact that it is used in modern combined-cycle gas turbine plants. A combined-cycle plant is one in which waste heat is captured and redirected to drive a mechanical system that powers a generator that creates additional electricity. These plants can be nearly twice as efficient as conventional single-cycle plants. In addition, if combined with cogeneration (the trapping of the last bits of heat for local home heating or other purposes), they can reach efficiencies of nearly 90%. That means that nearly all the heat released by burning the fuel is captured and used—an impressive accomplishment.
In theory, you could build a combined-cycle plant with coal (or other fuels), but it’s not often done. You can also increase coal efficiency by pulverizing it, and using a technique called “ultra super-critical black coal.” An expert report compiled by the Australian Council of Learned Societies in 2013 compared the efficiencies of a range of fuels, including conventional gas and shale gas, under a variety of conditions, and concluded that greenhouse gas emissions from electricity generation using efficient forms of coal burning were not that much more than from gas.
What this means is that most of the benefit natural gas offers comes not from the gas itself, but from how it is burned, and this is mostly because gas plants tend to be new and use more efficient burning technologies. The lesson, not surprisingly: if you burn a fuel using twenty-first century technology, you get a better result than with late nineteenth or twentieth century technology. This is not to defend coal, but to provide an important reality check on the discussion now taking place in this country. There is a real benefit to burning gas in America, but it’s less than often claimed, and much of that benefit comes from using modern techniques and new equipment. (If the coal industry weren’t so busy denying the reality of climate change, they might publicize this fact.)
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