Why is methane so important?
Methane (chemical symbol: CH4) is one of the main pollutants driving global warming. After carbon dioxide (chemical symbol: CO2), it makes the biggest contribution to greenhouse gases in the atmosphere.
It is actually a much more powerful greenhouse gas than carbon dioxide, because it has a much bigger impact per tonne on warming. It’s been estimated to have caused nearly a third of the global warming that we’ve suffered so far.
Methane is crucial to achieving the Paris climate agreement goals because its contribution to global warming is intense and brief – if we cut methane emissions by half by the end of this decade, the rate of warming we’re experiencing right now could be slowed by 30% keeping the window open to prevent temperatures rise above 1.5 or 2 degrees.
What’s it got to do with coal mines?
Coal mines are one of the largest sources of human-generated methane emissions in Australia. Coal mining releases methane that is trapped in coal seams and surrounding rock formations. These are referred to as “fugitive” emissions because they’re sneaky – hard to trace, hard to catch.
Fugitive methane emissions are leaks, losses and releases of methane that begin during mining and continue long after mining has ceased.
Do we even know how much the coal industry is polluting?
Fugitive emissions are usually estimated rather than actually measured, except in the case of underground coal mining. There’s growing evidence Australia is seriously underestimating how much methane is going into the sky from coal mining.
The International Energy Agency’s latest Global Methane Tracker Report estimated coal mining methane emissions in Australia could be 60% higher than the government reported, and they’re growing.
Emissions rates vary wildly from mine to mine depending on the type of mining, depth of extraction, carbon content, stage of operation and the natural variation within the geological formations targeted by the mine. Of Queensland’s 54 coal mines, two account for 29% of reported emissions and of the 39 coal mines in NSW, two are responsible for 24% of reported emissions. As a general rule, we can expect methane emissions to be greater in underground mines compared to open cut and to increase with depth of mining.
Why do underground mines create so much more methane?
Methane concentrations in rock beds tend to increase with depth of mining, and underground mines tend to be deeper.
In underground coal mines, there are two main types of fugitive methane emissions: “rich gas” that leaks directly to the surface, and ventilation air methane (VAM) which is methane that gets mixed up in the mine’s ventilation system. Without ventilation, underground mines would be deadly for coal miners, but once fugitive methane has been mixed up in the ventilation system it is incredibly hard to catch it back again before the air is vented into the sky.
Rich gas, that is, gas that is more purely just methane and not mixed with carbon dioxide and other gases, can be drained, captured and used for power generation before mining starts. VAM is present in concentrations too low to capture with existing technology, and must be vented for safety reasons.
Is there any way to catch these fugitives?
If the methane gas is pure enough, and the geology works, methane can be drained from the coal seam before mining starts. There are Australian coal mines that do this, but it’s not possible for all of them. Some mines have even claimed that they would need to use fracking to get the methane moving ahead of mining. Most companies with open cut coal mines say draining the methane first is too expensive and difficult.
Once it’s drained, it’s still got to be disposed of: Flaring releases carbon dioxide, a less potent but much more persistent greenhouse gas, into the atmosphere, burning gas for power generation likewise creates greenhouse emissions.
While high concentration methane can be captured and used prior to mining, “ventilation air methane” or VAM is methane that gets mixed up with air in the mine’s ventilation systems. This ventilation and mixing is crucial for the safety of workers, but it means that the methane in the mine’s ventilation air occurs at very low concentrations which cannot be abated using available technology. Because managing low concentrations of methane is a very challenging and costly exercise, it is common practice to release VAM into the air by venting or burning, thereby exacerbating global warming effects.
How many years has the coal industry been studying methane without actually reducing it?!
For at least 20 years, universities, the CSIRO, mining companies and engineering firms have been studying how to reduce methane pollution from coal mining and in all that time, it’s been increasing, because mining has been increasing.
The International Energy Agency says that “One of the most effective ways to cut down on coal mine methane is likely to be to cut coal consumption itself.”
That makes sense, because year after year, companies keep saying preventing fugitive methane is difficult, expensive and not possible.
There are 57 operating coal mines in the Safeguard Mechanism and the priority for the national and state governments must be ensuring that these facilities actually reduce their emissions, year on year.
For the dozens of coal mine expansion projects proposed in NSW and Queensland, the solution is even simpler: The International Energy Agency’s Net Zero by 2050 Roadmap for the Global Energy Sector is clear that “beyond projects already committed as of 2021 … no new coal mines or mine extensions are required.”