According to Colorado State University’s ‘Source’:
A new study that draws on previous work by Colorado State University scientists finds that the U.S. oil and gas industry emits nearly 60 percent more methane than current Environmental Protection Agency estimates. That amounts to 13 million metric tons of methane from oil and gas operations each year. The new Environmental Defense Fund study estimates the current methane leak rate from the U.S. oil and gas system is 2.3 percent, versus the current EPA inventory estimate of 1.4 percent. While the percentages seem small, the volume represents enough natural gas to fuel 10 million homes – lost gas worth an estimated $2 billion.
Okay, so we’re losing a lot of gas in the network of natural gas infrastructure between production and end use. But beyond the fiscal implications for mineral owners and others, what are the environmental impacts of raw methane leaking into our atmosphere? Does natural gas make more sense than coal and oil from an environmental life cycle perspective?
As is widely known, methane is over 20x more potent than carbon dioxide in short-term global warming impact. According to the study, the climate impact of 13 million metric tons of methane over a 20-year time horizon roughly equals that from the annual CO2 emissions from all of the coal-fired power plants operating in the U.S. in 2015. And previous work by Ramon Alvarez and colleagues (2012) assessed the potential climate benefits of natural gas vehicles and power plants vs. gasoline cars, heavy-duty diesel vehicles, and coal power plants.
Each of the three curves within the three panels of this graphic represents a distinct choice and its associated emission duration: for example, whether to rent a CNG or a gasoline car for a day (dotted line); whether to purchase and operate a CNG or gasoline car for a 15-yr service life (dashed line); and whether a nation should adopt a policy to convert the gasoline fleet of cars to CNG (solid line).
The red line has been added to Alvarez’s graphic to represent the leakage rate of 2.3% so that we can more easily make energy decisions that account for climate. What this shows is that it generally doesn’t make much difference to replace light-duty gasoline vehicles with CNG vehicles, and would even be climate negative when considering a widespread replacement of those vehicles at the national level (as there is a ~50-year climate ‘payback’ on that measure). Further, it is definitively climate negative to replace heavy-duty diesel vehicles with heavy-duty CNG vehicles. On the other hand, there are significant benefits to switching coal-fired power plants to natural gas.
Of course, this is just a snapshot in time that captures methane leakage rates as they are today. The new study states that “abnormal operating conditions” at certain liquid storage tank hatches and vents are likely responsible for significant leaks. The authors report an “urgent need to complete equipment-based measurement campaigns that capture these large emission events, so that their causes are better understood”. They identify a set of mitigation strategies that could help reduce leakage. If we get that down significantly and reliably, perhaps CNG vehicles could compete from a climate standpoint with gasoline or diesel vehicles. But until then, buyers be aware.