11/08/2014 12:17 BST | Updated 10/10/2014 06:59 BST

We Must Control Emissions to Make Sure Gas Really Is Cleaner

The majority of the UK public would support fracking if it is part of an energy mix that includes renewables, reports BBC news today.

I'd agree that natural gas will be a useful 'bridge' fuel in our transition away from coal and oil, and could balance the intermittent supply from renewables by providing a more adaptable form of electricity supply.

There is also no doubt that gas is cleaner in combustion than coal and oil, emitting 25-30% less carbon dioxide emissions than oil and 40-50% less than coal per unit of energy produced.

But whilst combustion is the major source of emissions from our gas use, it is not the only source. The case of shale gas has drawn attention to the issue of fugitive emissions or leaks from the gas supply chain as a whole, and it's not an issue we can ignore.

Robert Howarth and his team at Cornell University in the United States controversially kicked off this debate in their paper, stating that, over a 100 year timeframe, shale gas is about as polluting as coal because of the amount of methane leaked from both the fracking process and the transport of gas to where it is used.

This is partly because of the high global warming potential (GWP) of methane: when leaked directly into the atmosphere, its climate change impact is at least 25 times that of carbon dioxide over a period of 100 years.

There is no debate about this figure in the scientific community. In fact, if Howarth were to run his numbers again based on up-to-date emissions factors, the picture would be even worse. The latest report from the Intergovernmental Panel on Climate Change increased the estimate of the impact of methane from 25 times that of carbon dioxide to 28 times; and stated that when the 'climate-carbon feedback' impact of the gas is incorporated, the GWP increases to 34 times that of carbon dioxide.

The other main element of Howarth's calculation was the leak rates he used from both the fracking process and the gas supply chain.

It is the first of these - the leak rate from the fracking process - that has been the primary source of debate and hence the subject of a large number of scientific studies. The National Oceanic and Atmospheric Administration corroborated the higher end of Howarth's range, with other studies coming in at the lower end. Additional studies are due for publication throughout 2014.

It will be difficult however to apply these learnings to the UK, as hydraulic fracturing processes are likely to be different here to the US. For example some practices, such as allowing fracking flowback water to sit in evaporation pools, have contributed to methane emissions in the US but will not be allowed in the UK.

The second part of the calculation - leak rates in transporting the gas - has been much less in the spotlight. Few new studies have been commissioned, and it is even harder to transfer knowledge from one country to another due to the large variations in the state of the gas grid and how it is monitored in each place.

In the UK, Ofgem recognises the contribution of gas transmission and distribution to the carbon footprint of the gas supply chain and has created a financial incentive of around £0.5bn for the networks to reduce fugitive losses. As a result, the UK networks model the reductions in leaks that they are likely to obtain from measures such as replacing the old cast iron mains, the sources of many leaks in the distribution system.

Amidst the controversy and continued discussion of shale gas and Howarth's paper, it's easy to forget that currently all of our gas comes from conventional sources, which are themselves not leak-free. The leak rate of conventional oil and gas extraction is commonly cited at around 0.5-2% of the gas produced over the lifetime of the well, but in reality this is likely to vary hugely from facility to facility.

With the pressure mounting from groups concerned about shale gas, now is the time to review all monitoring procedures across the supply chain. The focus on shale gas has ensured shale will be well covered by research: in addition to numerous studies in the US, UK policy-makers are due to commission their own research, and the National Physical Laboratory and partners are undertaking a Climate-KIC funded project to measure emissions from UK-based shale operations.

What is required is an expansion of this focus to include other elements of the supply chain. We need to implement best practice that supports the detection of and reduction in fugitive emissions from existing conventional facilities, and the gas grid, as well as new shale. Otherwise we run the risk that gas may not be as clean an alternative as we would like - and as it could be.

A version of this article was first published on the ResPublica site.