Figure 1: Methane emissions from natural gas fields are much larger than the industry claims. (Nature, 2012)
I have written before about why natural gas is not, as is fashionably believed, a bridge fuel to a zero-carbon economy. Even if gas were cleaner than coal, it’s still a fossil fuel and switching to it would still cause dangerous levels of global warming. But whether you can call gas a low-carbon fuel in the first place is very questionable.
Natural gas is composed of methane (CH4), and when burned for energy it results in emissions of carbon dioxide (CO2). Both carbon dioxide and methane are greenhouse gases. While only carbon dioxide remains in the atmosphere for millennia, methane has a much stronger warming effect on human timescales (~100 times more powerful on a 20-year timescale; ~25 times greater on a century timescale). A methane spike in the next few decades could set off slow feedbacks also leading to greater warming over the long term.
The gas industry and its friends in government advertise gas as “clean energy” because the carbon dioxide emissions from burning it are less than those from coal. What they don’t tell you is that along its journey to being burned, unknown amounts of methane leak out. This is particularly evident during the process of hydraulic fracturing (“fracking”) used to extract unconventional forms of gas like shale gas and coal seam gas. A 2011 study estimated that when these leaked methane emissions are taken into account, shale gas is comparable to coal over 100 years, and much worse over 20 years.
Because the industry has been uncooperative, real-world measurements of these emissions have been elusive – until now. US National Oceanic and Atmospheric Administration (NOAA) scientists testing for smog in Denver, Colorado accidentally discovered methane leaking from a nearby shale gas field. They found the emissions were far more significant than the industry has claimed: 2.3-7.7% of the gas being extracted was leaking onsite (not counting any further losses during transport). Given how powerful methane is, a leakage rate of even 2% is enough to offset any benefit of replacing coal.
It isn’t clear whether observations of leaking shale gas at a single site in the US can be extrapolated to Australian coal seam gas; more investigation is needed on this. Astonishingly, Australia’s National Greenhouse and Energy Reporting System (NGERS) currently applies outdated US industry reporting methods to coal seam gas (and we’ve just seen how unreliable the industry’s claims can be). There are no independent Australian measurements. Last year, climate change think tank Beyond Zero Emissions (BZE) accused the consultancy WorleyParsons of burying a report on Australian coal seam gas emissions. The Australian Government has also refused to release research on the matter.
We should not rush into a natural gas boom before we understand its consequences. Instead we should shift investment to the genuinely zero-carbon renewable alternatives, which are already available and necessary for the desperately needed rapid transition to a zero-carbon economy.