In the past week there have been several reports and articles released discussing methane emissions (or leaks) from natural gas systems. With the current interest surrounding this topic, we wanted to bring you up to speed on the latest information.
Addressing the “Methane Leaks from North American Natural Gas Systems” paper
This recently published paper ran in Science Magazine and claimed that there are higher-than-expected methane emissions from natural gas systems –such as pipelines – around North America. One of the findings also stated that there is no benefit to switching diesel vehicles to run on natural gas.
So basically, instead of going onto locations and directly measuring emission rates from engines burning natural gas, the authors relied on data that only estimated what emissions would be – and did so at a rate far below of what engines in the field are capable of.
ANGA goes on to further explain:
The paper’s authors outline a number of causes for uncertainty, and so we outline them here:
When determining the emissions from the natural gas production process, activity data is important. Adam Brandt, the paper’s lead author, concedes this point and notes that data should improve with increased reporting requirements by the EPA. The EPA has published data for 2011 and 2012 showing a drop in methane emissions. While a modest drop, it occurred despite increased natural gas production.
Brandt also identifies clear challenges associated with estimating natural gas sector emissions by using an atmospheric approach (“top-down”). The most significant of these being how observed concentrations of methane are attributed to potential sources. Does the methane come from fossil sources rather than naturally occurring ones? The authors point out that studies can differentiate liquid petroleum and natural gas sources from coal, but are quick to admit that attributing methane emissions to the natural gas system is “more challenging.”
Brandt uses EPA’s Greenhouse Gas Index as a comparative baseline to illustrate how it under-reports methane emissions compared to measurement-based studies. Estimating methane emissions is a complex and difficult task, and it should be noted that the EPA changes its Inventory every year. The magnitude of these changes can be significant.
In the blog’s conclusion, ANGA states that more information is required to accurately identify the sources of methane emissions to help limit them during natural gas development.
EPA’s Greenhouse Gas Inventory
Energy InDepth highlighted the findings:
The downward trend that EPA identifies is arresting. In last year’s Greenhouse Gas Inventory, EPA found that methane emissions from natural gas systems had fallen 10.2 percent since 1990, and emissions from field production had fallen 38 percent since 2006. Those emission rates were already well below the threshold for natural gas to retain its clear environmental benefits. In its latest report, EPA finds that methane emissions fell 16.9 percent since 1990, with field production emissions falling more than 40 percent since 2006.
And in an interesting move, the EPA no longer considers natural gas systems as the largest source for methane emissions – it has been surpassed by enteric fermentation. [Enteric fermentation involves cows, for those who are curious]
The EPA’s report also talked about more than methane emissions.
From EID’s blog:
But the decline in methane emissions isn’t the only good news from the report. There has also been a sustained decrease in CO2 emissions, thanks largely to our increased use of natural gas. From the report:
“In 2012, total U.S. greenhouse gas emissions were 6,501.5 Tg or million metric tons CO2 Eq. Total U.S. emissions have increased by 4.4 percent from 1990 to 2012, and emissions decreased from 2011 to 2012 by 3.3 percent (225.0 6 Tg CO2 Eq.). The decrease from 2011 to 2012 was due to a decrease in the carbon intensity of fuels consumed to generate electricity […] with increased natural gas consumption.” (2-1)
Summarizing the methane emission findings
What to take away regarding emissions:
- The report in Scientific America is flawed for suggesting that switching vehicles from diesel to natural gas has no environmental benefits due to using hypothetical numbers rather than collecting data in the field.
- The EPA reports that the methane emission rates from natural gas systems have declined significantly despite the increased production and infrastructure in the U.S.
- There is a continuation of a reduction of CO2 levels in the U.S. led by the movement to switch power plants from burning coal to natural gas