CC: T Evanson
For half a decade, researchers have tried to answer
the question of how much methane escapes from natural gas wells
into the atmosphere. The recent emergence of fracking and shale gas
has brought the issue to the fore. But studies continue to present
Natural gas is mainly methane, some of which escapes during the
drilling, extraction, and transportation process. Such outbreaks
are known as fugitive emissions.
They're a problem because methane is a potent greenhouse gas -
25 times more powerful than carbon dioxide over a 100 year
timescale. The issue has been thrown into sharp relief because
gas production has undergone a boom in recent years.
The discovery of large amounts of gas locked in shale rock means
the US's production has
increased by about 25 per cent in recent years. That's
push energy prices down and
reduce the US's emissions. Many other countries are now also
keen to explore shale gas's potential, citing the US as an
Gas emits about half the carbon dioxide of coal when it's
burned, leading some to tout it as a
relatively "clean" fuel. But if fugitive emissions are too
high, it makes gas a less attractive fuel for policymakers and
industries interested in reducing greenhouse gas emissions. And so
the question of just how big fugitive emissions are is a pressing
The data is contested. Some people - often advocates of
decarbonisation - suggest the fuel is
nowhere near as "clean" as some companies declare. Others
- often industry voices - accuse campaigners of
There's certainly a wide range of estimates on the extent of the
Estimates of gas production leakage rates are expressed as a
percentage of total production. When we looked at this question in
2012, they ranged from 0.6 to
four per cent.
Over the past two years, the upper end of this range has
increased. Some studies now suggest the amount of gas leaking from
wells could be as high as nine per cent.
We've put some of the key estimates in the chart below:
Source: Various, see
this Google Doc for details. Graph by Carbon Brief. Note:
^ means value is for unconventional - i.e. shale - gas wells only,
* means the value in the graph is the mid-estimate or mean of a
range where a 'best estimate' is not given.
So why is there such a range of results?