sectoral economic costs and benefits of ghg mitigation - IPCC

Jonathan Stern
Energy Research Institute targets would not only improve local air quality considerably but also,
the Institute estimates, would save 70 million tons of carbon per year.
The consequences for the model are that if these higher gas demand figures are achieved, then it
is difficult to see how the Bartsch/Müller Kyoto reductions from BAU can be achieved because
they would need correspondingly higher reductions from other regions – probably OECD. But
for carbon emission reduction targets as a whole the problem appears to be that if these ambitious
targets are not achieved, the alternative will be to burn coal rather than gas with correspondingly
higher carbon emissions.
Methane Leakage
The Bartsch/Müller paper appears to make assumptions of very high methane leakage (fugitive
methane) from EIT gas systems. This requires some general comment on methane leakage and
some specific comments on the nature and extent of leakage in EIT systems – specifically Russia
and Ukraine.
In general terms, methane leakage needs to be distinguished from flaring of gas associated with
oil production. This practice is becoming less usual but still occurs when there is no
infrastructure to gather this valuable fuel. Nevertheless, although this practice produces carbon
dioxide emissions, it is not as damaging – in greenhouse gas terms – as “venting”, where gas is
simply released with no combustion taking place. 1 This can be equated with the release of
methane at the production stage for both oil and gas.
“Leakage” of methane from natural gas pipeline systems is extremely difficult to measure.
However, the vast majority of leakage takes place at the distribution – i.e. low pressure – end of
the gas system, rather than in the transmission (i.e. high pressure) system. This is particularly the
case for town gas networks – built in the 19 th century (found in many OECD countries) which
have been converted from town gas (based on coal and naphtha) to natural gas in the past half
century. Any relatively modern high pressure transmission system (built in the past decade)
should be able to achieve leakage rates of significantly less than 0.1%; modern distribution
systems may have slightly higher rates.
The problems at the customer end of a natural gas system form the crux of the estimation and
measurement problem. Measurement of leakage depends on accurate metering. Modern metering
systems are a great deal more accurate than their predecessors, but remain subject to error.
Moreover, a great deal of gas will “leak beyond the meter”, i.e. gas will be inadvertently vented
by the customer. This is why methane detection programmes in urban areas may not be
registering gas leaking out of pipes, so much as gas from appliances that customers have failed to
secure properly. To return to the metering problem. Every large gas system will have, in its
physical accounting process, an item labelled “unaccounted for gas”. This is the difference
between the volumes which a company has metered into its system, and the volumes for which it
has billed its customers as a result of meter-readings (after any gas used for compression has
been taken into account). Thus “unaccounted-for gas” will include leakage from the system, but
will also include metering errors and gas which has been stolen by customers (which can be a
relatively high volume in some countries). 2
1 Until relatively recently this was practiced in production locations such as Texas where it was considered
safer than flaring gas.
2 A significant number of gas explosions in the residential sector are caused by customers who are
attempting to by-pass their meters.
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