Coal’s dirty secret

Coal mining globally releases millions of tonnes of methane every year, a potent greenhouse gas which adds to coal’s considerable climate impact. Even though coal operators know exactly where their methane leaks are, accurate measurement or reporting of them is rarely required, leaving governments in the dark about this hidden climate multiplier.

Coal is known to be ‘dirty’ because of the emissions and pollution produced when it is burnt to produce electricity and steel. However, the climate impact of burning coal is considerably larger once we factor in the methane emissions associated with mining it.

Methane is trapped inside and embedded throughout coal seams, and is released to the atmosphere before, during and after mining. As a potent and fast-acting greenhouse gas, it is 82.5 times more powerful than carbon dioxide over its first 20 years in the atmosphere, and 29.8 times more powerful when averaged over 100 years. This is why methane has important implications for climate change, particularly in the near-term.

According to the IEA, reducing methane emissions from the energy sector is one of the best–and most affordable–opportunities to limit global warming in the near term. According to their global estimates, emissions from coal are just as large as those from the oil or gas sectors respectively. However, reliable national emissions estimates for the coal sector are particularly hard to come by, leaving most governments in the dark when it comes to understanding the scale of their methane problem, and the importance of tackling it. 

150 countries have signed up to the Global Methane Pledge, a commitment to a collective reduction in methane of 30% overall. However, while more than 50 countries, including both the US and China have developed or are developing economy-wide methane action plans, only the European Union and Canada have thus far committed to specific actions to reduce active coal mine methane emissions.

Even today, coal operators know the exact location and sources of their coal mine methane emissions in order to prevent explosions. A major part of safely operating an underground coal mine is removing the methane which is released underground and venting it to the atmosphere. This methane will either be emitted at the drainage station or from ventilation air shafts. Methane from surface mines is vented directly to the atmosphere as the coal is mined.

Despite knowing these sources, efforts to accurately measure or mitigate them are rare. In many cases, coal operators are not required to report the methane measurements they do make to the government or public, who instead rely on emission estimates which have been found to underestimate emissions in some cases by a factor of 30.

Additionally, no government has implemented systematic third party verifications or checks to confirm the measurements and estimates provided by coal operators in the first place, despite the availability of satellite monitoring.

There are two different methods which can be used to estimate and validate emissions. 

“Bottom up” methods are based on using inventory/facility level data and aggregating that to produce an estimate at a national or global level. As facility-level measured data is often not available, emission factors are used instead. 

Coal mine methane emissions factors are an average estimate of how much methane is emitted per tonne of coal, but it is uncertain how well they reflect actual emissions, which vary by geography, geology and other factors.

Governments report bottom-up CMM estimates to the United Nations Framework Convention on Climate Change (UNFCCC). Their estimates rely in large part on applying methane emission factors to activity (i.e. coal production) data rather than relying on facility-level, measured methane emissions. The emission factors used by governments can be typically very uncertain, in some instances by a factor of 2 or more. 

“Top-down” methods are based on measured methane observations, for example satellite measurements, and combined with bottom-up information to model emissions. They are often used to improve global, or national scale emission estimates.

Both methods generally have large uncertainties due to the lack of comprehensive data from all major producing countries.