Natural Gas. Burning it turns out to be not as bad as not burning it. (Photo credit: todbaker)
It may turn out that greenhouse gas (GHG) emissions are higher from using natural gas to produce electricity than from using coal. Or are they?
The possible culprit of these GHG emissions is fugitive emissions of methane. Since methane is a far more potent GHG than CO2, this is bad. Fugitive losses include loss of methane from the well-head during flow-back return of the fluids, during drill-out following fracturing and during well-venting, plus losses from equipment leaks, losses during transport, storage, and distribution, processing losses and losses during liquid unloading. (Is methane coming out of your faucet fugitive?)
Traditionally, we use emission numbers just for the power plant itself, that is, how much CO2 does a coal plant emit in producing a kWhr of electricity versus a gas plant versus a wind turbine, etc. These numbers have some emissions from other parts of the plant life-cycle such as construction and mining, as these dominate the emissions for energy sources like nuclear, hydro and wind which emit no GHG during operation.
Until now, the average equivalent grams of CO2 emitted per kWhr produced has been calculated as 975 gCO2/kWhr from coal; 600 gCO2/kWhr from natural gas; 90 gCO2/kWhr from hydro; 55 gCO2/kWhr from solar; 15 gCO2/kWhr from wind, and 15 gCO2/kWhr from nuclear (Parliamentary Office of Science and Technology; GHG from Power Plants). And that may be correct. However, new studies by Robert Howarth and associates at Cornell University (GHG Footprint of Natural Gas; National Climate Assessment; thanks to atomikrabbit for pointing me in this direction) provide emissions data from the entire natural gas life-cycle. Their results bump this number for gas from 600 gCO2/kWhr to over 1,200 gCO2/kWhr, making natural gas the largest emitter of GHGs in electricity generation. On the other hand, Howarth and company have been challenged by others that say their numbers are too high (BusinessWeek), particularly Lawrence M. Cathles, also of Cornell. Cathles contends that gas is still better than coal with respect to global warming. Even if Cathles is correct and 600 gCO2/kWhr is still the number for gas, it's not that much better than coal compared to ther energy sources like hydro and nuclear.
Methane is a powerful GHG, with a global warming potential that is twenty times greater than that of carbon dioxide. However, this effect is time-dependent - it matters when the gas is emitted and how long it stays in the atmosphere, and that is part of the controversy. Methane effects peak over the first two decades following emission, and this is the exact time frame in which we need to act in revamping our energy mix.
Escape of these fugitives is especially large for shale gas as it requires high-volume hydraulic fracturing, or fracking. Fracking forces large volumes of water under pressure into the shale to fracture and re-fracture the rock to increase gas flow. A large amount of this water returns to the surface as flow-back within the first weeks after injection, bringing back large quantities of methane.
These losses can be decreased if new technologies are used and if regulations are strengthened (EPA 2010) like using smart automated plunger lifts during liquid unloading, use of flash-tank separators or vapor recovery units, better storage tanks and compressors, and better leak detetors. Such improvements have resulted in lower emissions from gas production in Colorado versus those in Utah, but these methods are not yet being broadly implemented and it is up to individual States to act.
Tower for drilling horizontally into the Marcellus Shale Formation for natural gas, from... [+]
It is still true that gas does not have the nasty health effects that result from breathing burnt coal particulates, hazardous compounds emitted like mercury and lead, the air quality issues from NOx and SOx, and the environmental effects from mining. So coal is not off the hook for these problems. But we have to expand the non-fossil fuel sources quickly if we are to address global warming in any meaningful way.
If true in any sense, these new numbers for gas could become even more important if carbon-trading or C-taxing occurs as these schemes presently undervalue the warming effects of methane and the emissions from unconventional gas sources like shales and tight-sands. Many think we are destined to become a natural gas nation because natural gas is considered a bridge fuel from oil and coal to the non-fossil fuels.
Beware - this bridge may still get too hot before we reach the other side.
