It’s pretty obvious that traffic-clogged roads contribute to global warming – especially when you’re standing next to one, trying to avoid breathing in. But research released last week shows that greenhouse gases are also escaping into cities from a far less visible source: leaks in old gas pipes.
Natural gas is delivered from gas fields to urban areas, via hundreds of miles of piping. Once it reaches a city, that gas is delivered to buildings through a network of connections and valves.
And it’s here that the problem begins. Scientists at Harvard University have found that, in Boston, old pipes, valves and other bad connections are leaking massive amounts of gas every year. In fact, the study estimates that around 2.7 per cent of all the gas piped into the city escapes at some point in the delivery process, rather than 1.1 per cent as was originally thought.
That's the equivalent of 200,000 homes's supply, valued at around $90m a year. But the more worrying statistic is that, depending on the season, escaped natural gas accounts for between 60 and 100 per cent of all the city’s methane emissions.
This is the first study to pin down the contribution of piped gas in particular to methane emissions. Methane is released from many sources – sewage, farming, landfill – but natural gas also contains ethane, another carbon-based gas. The Harvard researchers used sensors at different heights and locations to measure methane emissions with traces of ethane, so they could estimate which emissions were caused by natural gas leaks.
Other cities which use a lot of natural gas and have an older pipe system may be facing similar problems to Boston. Kathryn McKain, who led the Harvard study, said that US government policy on methane emissions has included little or no discussion of pipe leaks:
There’s been a lot of interest in controlling methane emissions, but emissions from the distribution and use side of the natural gas system have been almost absent from the recent national policy conversation.
For years, environmental scientists have known that oil and natural gas fields leak methane into the environment: hack your way into a seam of gas or oil and it's inevitable some will escape into the atmosphere. But this study is the first to point out quite how dangerous and wasteful old and badly-maintained gas pipes can be.