A belching coal plant is easy to identify as a probable greenhouse gas polluter. Coal emissions are point source pollution—like a chemical spill in a stream, the pollution can be traced back to a specific activity at a precise place.

But is measuring the carbon produced at a power plant the best way to monitor emissions? A team of scientists recently took a different approach to estimating carbon dioxide: the bottleneck method. Instead of considering the pollution emitted only at the end use, burning phase of fossil fuel use, the researchers considered all phases: mining, transport, refining, and burning.

Their study identified the worst emissions offenders, and the results were surprising: oil and gas pipelines. The researchers noted that the companies enabling greenhouse gases emissions are most at risk of climate mitigation lawsuits. //

The bottleneck analysis showed that 9 of the top 10 carbon polluters were oil and gas pipelines (47% and 44%, respectively), while a coal mine took the remaining spot in the top rankings. In comparison, point source methods revealed that the top 10 polluters were oil pipelines (eight spots) and coal mines. //

For natural gas, the biggest emissions came from pipeline transport. The sheer length of pipelines—the Transcontinental Gas Pipeline (Transco) alone branches into more than 16,900 kilometers (10,500 miles) of pipeline from Texas to New York—means there are lots of places to emit gas.

“Especially for older pipelines and pipeline networks, you get leaking. And methane is a pretty severe greenhouse gas,” said Pearce. He noted that fixing or not fixing leaks can be an economic decision for pipeline owners—minor leaks might cost more to repair than the loss of gas into the air.