Gas distribution systems may be emitting materially more methane than prevailing estimates suggest, an Environmental Defense Fund scientist said in a preview of research that the group plans to publish soon.
Existing data on methane emissions from gas utility infrastructure is based on the number and volume of leaks the companies report. Steven Hamburg, chief scientist for the Environmental Defense Fund, or EDF, said at the World Gas Conference that research has shown that these leak reports might be low.
"[Gas utilities are] a more important source. I feel very confident in saying that," he said at the Washington, D.C., event. "All the indications are skewing one direction, that there are these emissions."
The EDF, in partnership with Google Earth Outreach and other researchers, has mapped leaks in a number of utility service territories. As part of a recent large-scale study, the researchers consistently found more leaks than companies had reported, Hamburg said.
"When you look at the distribution of those emissions, those leak indications, what you see is the activity factors — the number of leaks being reported by utilities — is significantly smaller than the actual population," he said. "That's one factor."
The leaks also appeared to be larger than the utilities had previously thought, furthering the expectation that the distribution systems' emission are greater than the sector and the U.S. Environmental Protection Agency indicate. How different the emissions may be from the current estimates remains to be seen, however, as the EDF study Hamburg referenced is still going through the peer review process, he said.
The study looked only at utility-owned infrastructure, not measuring emissions beyond the meter. Other studies are ongoing to collect more data on how often end-use equipment — such as stoves, water heaters and furnaces — releases methane, Hamburg said. Ambient emissions measurements have indicated that utility system leaks do not account for all the methane releases in a company's service territory, leading some researchers to conclude that there are likely downstream leaks adding to the total methane levels, he said.
The EPA's most recently released greenhouse gas inventory indicated that among methane emissions from natural gas systems, distribution systems contributed about 7.3% in 2016. The production sector released an estimated 65% of gas system methane emissions.
Production emissions have risen substantially since 1990, up about 58%, although the amount of methane released in 2016 was down slightly compared to the previous year, according to the EPA. Distribution systems, by contrast, have been responsible for an estimated 72% decrease in methane emissions since 1990.
The upcoming EDF research may indicate that that decline has been less dramatic, but the utility segment is likely to remain a much less significant methane emitter than other parts of the oil and gas industry, Hamburg said.
"My speculation ... [is] it won't dwarf what's going on in the upstream portion, but it is going to be higher than the numbers we see," Hamburg said.