February 19, 2020

expert reaction to study looking at recalculating human-generated methane emissions

Research, published in Nature, reports that man made methane emissions may currently be underestimated.

Prof Dave Reay, Chair in Carbon Management, Executive Director Edinburgh Centre for Carbon Innovation, University of Edinburgh, said:

“This is a salutary reminder of just how uncertain our accounting of global methane emissions actually is. The study blows a sizeable hole in the natural methane budget and instead points the finger firmly at human activity, and specifically our extraction and distribution of fossil fuels. We tend to use so-called ‘bottom-up’ estimates for these emissions – taking some individual site estimates or spot measurements and multiplying them up to cover all fossil fuel extraction globally. In this case the bottom-up approach appears to have been woefully inadequate.

“Methane concentrations in our atmosphere have more than doubled since the industrial revolution and this increase has further accelerated in recent years. We knew fossil fuel extraction – including fracking – was a major part of global methane emissions, but this impressive study suggests it is a far bigger culprit in human-induced climate change than we had ever thought. If correct, gas, coal and oil extraction and distribution around the world are responsible for almost half of all human-induced methane emissions. Add to that all the carbon dioxide that is then emitted when the fossil fuels are burned, and you need look no further for the seat of the climate emergency fire.

“Rapidly cutting methane emissions from fossil fuel extraction and distribution – such as through reduced leakage from well sites – was already important for achieving the Paris Climate Goals. This study suggests those cuts are more vital than ever.”

Dr Phillip Williamson, Honorary Reader, University of East Anglia (UEA), said:

“Carbon dioxide isn’t the only greenhouse gas causing climate change; increasing methane also contributes, with human activities adding extra methane to what is already in the atmosphere due to natural releases. Using sophisticated techniques to analyse the air trapped in polar ice, Benjamin Hmiel and colleagues show that natural methane emissions seem to have been greatly over-estimated.  Instead of 40-60 million tonnes per year from geological sources, the actual value needs to be revised downwards – to as little as 2 million tonnes.

“These results indicate that human activities are inadvertently responsible for much more of the problem of rising methane.  Yet that is actually good news, since it should mean that there are now greater incentives to prevent methane leaks from oil and gas extraction.  Furthermore, the phase-out of these fossil fuels on the pathway to net-zero will bring the bonus of reducing atmospheric methane more rapidly than we had expected.”

Dr Jasmin Cooper, Sustainable Gas Institute, Imperial College London, said:

“There is currently not enough data to accurately say how much methane is produced in the extraction of fossil fuels, however this paper’s finding that methane emissions are underestimated is in agreement with other studies.

“This study reached its estimate through the use of core sample analysis, which is different to traditional methods of measuring methane emissions. Traditionally, methane is measured from either onsite measurements or from overhead air sampling. The method used in the study has elements which fall into both measurement methods.

“In addition to the Alvarez study cited in the paper, there is a Dutch study which found fossil fuel methane to be higher than inventory emission factors. However, the timing of top-down measurements is important because if measurements are taken during episodic events i.e. events not occurring during normal operation, the measurements can be an overestimate. There is a paper from the University of Manchester which used aerial sampling to measure methane during exploratory hydraulic fracturing, but one of their measurement days coincided with an cold venting event (gas that is vented because it cannot be flared), which resulted in much larger emissions than under normal operating conditions.

“There is an agreement in the natural gas industry that more actions need to be taken to measure and monitor methane emissions. Many companies have set greenhouse gas emission targets e.g. BP recently announced that they want to be a net zero company by 2050. The accurate measuring of emissions is important for companies to meet their targets. It is also important for identifying what the sources of emissions are (here there is another gap in the data) because without knowing where emissions are coming from, effective abatements practices/methods cannot be put in place.

“The assumption that methane gas is evenly mixed in the atmosphere is important for methods that extrapolate concentration measurements from specific regions/areas to the world. Some specific regions emit more fossil fuel methane than others, so estimating a global value based on measurements/samples from one area is complex and estimates may not be representative of the global situation.”

Dr Joeri Rogelj, Lecturer in Climate Change, Grantham Institute at Imperial College London, said:

“This new study brings both good and bad news for our ability to keep global warming in check.

“The bad news is that this study shows that human activities might well be responsible for a much larger share of the increasing methane concentrations in the atmosphere. In particular, the methane emissions from the extraction and use of fossil fuels might well be a quarter to 40% higher than earlier estimated. This indicates that the fossil fuel sector has a much more polluting impact beyond being responsible for the overwhelming majority of carbon dioxide emissions. This is worrying and overall bad news.

“This new study also provides some good news, because it shows us where we can act on climate change. Measures and policies to eliminate methane emissions from fossil fuels are well known, and in many cases even make sense from a narrow economic perspective. They range from eliminating leaking pipes, reducing or improving flaring, and evidently also a shift away from the extraction and use of fossil fuels towards renewable energy sources. What this study shows is that we can have a bigger impact on methane in the atmosphere than earlier thought. This allows us to set climate policy priorities right.

“Together with bringing down carbon dioxide emissions to zero, keeping methane emissions to as low as possible levels will result in stabilizing global warming. Trying to reverse our global warming contribution will require us to draw down carbon dioxide from the atmosphere.”

Dr Heather Graven, Senior Lecturer in Physics at Imperial College London, said:

“This is a very important study that suggests methane emissions from the fossil fuel industry have been underestimated.

“This means that the fossil fuel industry is likely responsible for an even larger proportion of recent climate change than we previously thought, but the good news is that the fossil fuel industry may now have a greater opportunity to mitigate climate change from methane.

“It’s critical that more effort is put into methane emissions mitigation such as fixing leaks in natural gas extraction and distribution networks. And we need to monitor these mitigation efforts using atmospheric measurements, including measurements of radiocarbon in atmospheric methane like those made in this study.”

Prof Euan Nisbet, Professor of Earth Sciences, Royal Holloway University of London, said:

“This is an important paper, written by an expert team. It has a sad implication, that human-made fossil fuel methane emissions are bigger than thought in earlier studies.  But that also means it has an optimistic implication – that the target for cutting methane is more accessible!”

‘Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions’ by Hmiel et al. was published in Nature at 16:00 UK time on Wednesday 19 February. 

DOI: 10.1038/s41586-020-1991-8

Declared interests

Prof Dave Reay: “No interests declared.”

Dr Phillip Williamson: “I have no conflicts of interest to declare.”

Dr Jasmin Cooper: No conflicts of interest.

Dr Joeri Rogeli: “No conflicts of interest, although I am:

– Coordinating Lead Author, IPCC Special Report on Global Warming of 1.5°C

– Lead Author, IPCC Sixth Assessment Report”

Dr Heather Graven: No conflicts of interest.

Prof Euan Nisbet: “No conflicts”