FAQs and general information regarding our recent paper “Four corners: The largest US methane anomaly viewed from space” and subsequent press coverage.
We very much appreciate the general interest that has been expressed in this work, and more broadly concerning methane emissions. We have received many questions and inquiries, and are doing our best to respond. Here we will provide some succinct summaries of the findings, and answer some common queries we have been asked.
As noted in the paper, the major findings of this work are:
- Four Corners exhibits the largest US methane anomaly seen from space, and this observation is validated with independent ground-based observations.
- Analysis of observations and simulations find emissions for this region of 0.59 Tg CH4/yr for the 2003-2009 time frame.
- The steady persistence of the signal from 2003-2009 is indicative established activities in the Four Corners region are responsible, and not the recent shale boom (more detailed comments on this below).
- This work demonstrates that space-based observations (in combination with transport modeling) can identify, locate, and quantify anomalous methane emissions source regions.
How important is this finding- what is the context of .59 TgCH4/yr?
As reported in the paper, this value approaches 10% of the US EPA estimated CH4 emissions from Natural Gas in 2008. The EPA inventory also consider many other sources of methane (such as landfills and livestock, for more on methane in the EPA inventory http://epa.gov/climatechange/ghgemissions/gases/ch4.html).
Total global methane emissions are ~550 TgCH4/yr, so 0.59 is only ~0.1% of global total emissions. For such a small region, it is a large number—it is very close to the estimated methane emissions from the entire UK oil, gas, and coal industries combined.
I’m confused—is this related to ‘fracking’ or not? I read some place this pre-dates ‘fracking’ and in others that ‘fracking’ has been occurring for decades in the San Juan basin?
This is an excellent question that requires some explanation of terminology. Unfortunately the term ‘fracking’ is used in a couple different contexts. In the past decade or so the US has experienced a transformation in oil and natural gas production. This transformation is linked to high-volume hydraulic fracturing (with horizontal drilling) in shale formations. Often, ‘fracking’ is used to refer to this recent advance. Hydraulic fracturing itself has existed for the last 50+ years, and has been carried out extensively throughout the US before the recent shale boom—including in coalbed methane recovery. Other forms of fracturing have also been pursued, including the nuclear fracturing experiments conducted in the later 60’s in the US (Project Gasbuggy). All of these can be referred to as ‘fracking’.
In the context of our study in Four-Corners, we are specifically commenting that based on the location and timeframe of the measurements, the signal observed in Four Corners is not related to the recent high-volume hydraulic fracturing in shale boom. Instead the signal observed is likely attributable to established fossil-fuel extraction activities that have been ongoing in the San Juan basin since at least 2003.
Ok, so what is responsible for the signal you see?
These observations see the total methane in the atmosphere in the region emitted by all local sources. We cannot from the space-based observations alone pinpoint the precise sources. In Four Corners, there are extensive gas, coal, and coalbed methane activities (as well as oil, geologic seeps and other sources). The Four Corners region is actually the largest coalbed methane production site in the US. Given the very large amount of natural gas (which is primarily composed of methane) produced from coalbed methane in Four Corners, it is likely much of the signal we observe is related to this activity. We will need to conduct further studies to be able to better pinpoint the specific contributing sources.
What is causing the large signal I see [or lack of signal I see] on the anomaly map over [pick your favorite region, CA, TX, PA]
Remember, this is a map of methane anomalies, and not a map of methane emissions. This is an important distinction, as the signals you see on this map are a combination of emissions and transport (e.g. winds). Imagine a case where you have high emissions, but persistent high winds—this will not produce a large signal on the map as the methane will be more distributed. Thus one has to be careful to read too much into seeing or not seeing a spot elsewhere. Our study focused on validating and understanding the Four Corners region—other regions would require separate focused study.
What is an anomaly? (and what are you measuring?)
In our study we use both space and ground-based observations. Both instruments measure the total amount of methane between the surface of the earth and the top of the atmosphere- from the ground this is for one location, and from space this is done over locations around the world. The US space-based anomaly is defined as the difference from the large-scale average, corrected for the impact of topography. This illustrates where regions have higher than average methane values.
What about other parts of the world?
Our study focused on the US, and in particular on the Four Corners region, and from this study we cannot draw any conclusions about elsewhere. If you are curious to investigate global methane maps, you can take a look at the following website which hosts space-based methane observation data and maps from the sensor we used in this study (http://www.esa-ghg-cci.org/?q=node/116).
What is the leakage rate you find in your study?
We do not report a leakage rate. This is because the observations we used ‘see’ all the methane emissions in the region. We cannot clearly attribute which portion is linked to, for example, oil versus gas activities in the region, and thus cannot produce an accurate leakage rate number for fairly comparing to leakage rate number reported in other studies or used by the EPA.