Methane Super-Emitters
New high-tech satellites produce detailed emissions images for this powerful greenhouse gas.
Methane - so many uses, so many sources, so many environmental impacts.
This simplest of all hydrocarbons, methane is just one carbon atom combined with four hydrogens. Chemically speaking it's CH4, a small molecule that has powered a major transition in electricity generation, and as a substitute for coal, has reduced both acid rain and carbon dioxide emissions, as well as the release of mercury, dust, ash, and other pollutants.
As a simple molecule, it can also be built up into a wide range of products. Recent research has simplified the first step in converting methane to propylene and ethylene, important feedstocks for many plastics.
On the other hand, methane is a potent greenhouse gas. You can find estimates of just how much more potent than carbon dioxide that range from 28 to 86 times. This confusing difference depends on the time frame. The 86 times is calculated over a 20 year time period after release to the atmosphere, while 28 times is over 100 years. This is because carbon dioxide lasts for hundreds of years in the atmosphere and methane only about a decade.
In absolute terms, one molecule of methane is something like 120 times as effective as one of carbon dioxide in trapping infrared radiation - the process that drives warming.
There has been an intensifying focus on methane over the last decade for 4 simple reasons:
- It is the second most important greenhouse gas
- It is increasing rapidly
- Emissions and impacts may be underestimated
- Some sources are theoretically controllable
This increased focus is due at least in part of the energetic efforts of Dr. Steve Hamburg, Chief Scientist and Senior Vice President at the Environmental Defense Fund, one of the oldest and most influential organizations dedicated to solving pressing environmental problems. We'll see what Dr. Hamburg has to say in a minute.
The Second Most Important Greenhouse Gas
The ability of certain gases to absorb infrared radiation, and so act as greenhouse gases, has been known since the 1850s. While water vapor is the primary gas warming our planet in this way, it is increases in carbon dioxide, methane, and other trace gases that are driving increasing temperatures. Carbon dioxide is the most important of these, but methane is not that far behind. Radiative forcing is the technical term used to describe how changes in concentration of different substances alter the energy balance, and hence temperature, of the planet. Measured in watts per square meter of Earth's surface, methane has contributed more than half as much to cumulative global warming as carbon dioxide.
Increasing Rapidly
While carbon dioxide is now about 50% higher than it has ever been over the last 800,000 year, methane concentrations have increased nearly three-fold.
Emissions and Impacts May Be Underestimated
Methane has a complex global cycle involving significant sources and sinks in the natural environment as well as major sources from human activity. In the natural world, methane is produced by microbes in the absence of oxygen and consumed by microbes when oxygen and other substrates are present. In this table of sources and sinks, the largest natural source of methane is from wetlands with their waterlogged and anaerobic (lacking oxygen) sediments. The natural sink for methane, in upland soils where oxygen is present, is much smaller than wetland sources. The most important "sink" for methane is through chemical reactions in the atmosphere (leading to that shorter residence time than for carbon dioxide).
The most important human sources for methane are related to food production and waste management. Both rice paddy agriculture (in waterlogged, anaerobic soils), and landfills and other waste management strategies are major contributors, as well what is politely called "enteric fermentation" or digestive processes in cattle.
Producing, processing, and transporting methane as natural gas is the other major human contribution, but not the actual burning of natural gas. Combustion converts almost all of the methane used to carbon dioxide.
It is that fossil fuel number that has been the focus of new studies and new technologies in an effort to get better numbers and devise more effective strategies for reduction.
So let's hear from Dr. Hamburg on this topic (this summary is paraphrased from this article and the PermianMAP website)
The Environmental Defense Fund (EDF) was founded by scientists and uses science to determine which challenges are most pressing and the most effective course of action to solve these challenges. Until recently, no one had rigorously measured the amount of methane that was escaping to the atmosphere from oil fields. The EPA relied on estimated emission factors not actual field measurements. In response, EDF established a series of studies in collaboration with hundreds of scientists starting in 2011 which included the PermianMAP initiative to measure and map methane emissions in the densely drilled heart of the Permian basin, one of the largest gas and oil producing regions in the world and the largest in the U.S., located in Texas and New Mexico.
Led by Dr. Hamburg, and in cooperation with other scientists, the PermianMAP initiative involved 5 levels of data collection. Field crews on the ground measured methane concentrations at precise points but for short periods of time. Permanently located towers with methane sensors provided continuous concentration data at a number of fixed points. Aircraft overflights sampled the integrated impact of emissions in the mixed atmosphere above the field while other aircraft used targeted images to estimate emissions from individual facilities. All four of these were combined with models of air flow across the field to generate emissions estimates. A final link was to remote sensing data produced by the European satellite-based TROPOMI instrument.
The result?
Emissions of methane from this major oil and gas producing region are, according to Dr. Hamburg, about 2.5 times previous estimates using simple, generalized emission factors most commonly applied by EPA and other agencies.
Partly as a result of this increase in focus, at the 26th annual international climate summit (COP26) in Glasgow, Scotland, more than 90 nations (and now more than 150) signed the Global Methane Pledge, promising to pursue a 30% cut in emissions by 2030. In the United States, the Environmental Protection Agency has proposed extending regulation of methane emissions to existing as well as new oil and gas wells and to charge fees for emissions. Many companies have made voluntary commitments to reduce methane emissions, though there is as of yet no data to suggest we are seeing major reductions.
But our focus in these Substack essays is not on policies, but on the numbers and how we get them, and especially on emerging technologies, so let's dive a little deeper into what those remote sensing satellites can see.
Here is a list of four research initiatives that have used or will use satellite remote sensing approaches. An interesting thing about this list is that while two are driven by national laboratories and public funding, often in partnership with private companies, the other two are being driven by private non-profit groups essentially funded by philanthropy and private investors.
All use essentially the same technology and approach, engineered in slightly different ways to optimize performance. That basic approach is called Imaging Spectrometry.
Picture a prism and the way a simple triangular piece of glass or plastic can separate white light into the range of visible colors we also see in a rainbow (you may remember ROYGBV from school days - red, orange, yellow, green, blue, violet). Maybe you have seen these prismatic rainbows projected on a wall or piece of paper.
There are also wavelengths, or types of light, that we cannot see. Ultraviolet light is high energy (short wavelength) light that can be damaging to human tissues. Those wavelengths would hit the wall beyond the violet end of the "rainbow" generated by the prism. Infrared light ("heat" radiation) has longer wavelengths and would strike the wall beyond the red end.
An imaging spectrometer can read the amount of energy received across all of these different types of "light" generating a spectrum like the one shown here for just part of the infrared region. When compiled across a two dimensional surface, the satellites generate a "data cube" of reflected light in space and by wavelength.
The key to using these wavelengths is that different compounds have very different patterns of absorbance or reflectance at very specific wavelengths. The one shown above is part of that spectrum for methane. Think of these as chemical "fingerprints" that allow, with some fancy math to remove the effects of other compounds, a measurement of the amount of methane present. Launched on a satellite, an imaging spectrometer of this type can measure the total amount of methane between the satellite and the ground.
I was part of a NASA science team in the early days of imaging spectrometry looking at applications for predicting carbon gain by forests, and remember well the first time we were presented with what is called a "focal plane" - the light sensitive surface that records light intensity across hundreds of wavelengths. About the size a post card, these units effectively counted individual photons, the smallest packets of light energy. The sensitivity seemed nothing short of miraculous then, and that technology is stone age in comparison to what the latest satellites can do.
There are lots of engineering specifics that affect the accuracy and frequency of measurements, and you can visit the sites listed in the table above to learn more about the different satellites, but the bottom line is that it is now possible to map methane concentrations at very high spatial resolution and so identify major pulses from high concentration sources or summarize smaller sources over an entire region.
The EMIT satellite operated by the Jet Propulsion Laboratory, a NASA research center, has produced some of the clearest images of methane emission plumes to date. Here is a sampling from the website for that project.
Methane Emissions are Theoretically Controllable.
We have focused here on one important and previously underestimated source of human emissions of methane: oil and gas field operations. Other steps in that supply chain can be addressed as well. This graphical summary of human-only sources of methane emphasizes that other processes, especially related to food and wastes could be increasingly important if fossil fuel sources are reduced.
While EPA emission policies might focus on natural gas and oil production and supply chain steps, there are other research programs underway designed to alter "enteric fermentation" sources (livestock in this figure) through dietary changes for cattle, and many examples where methane emissions from landfills are captured and burned as an energy source.
Steve Hamburg for one has said that he thinks the potential for reducing methane emissions could be a very important part of a low carbon future and is the most effective way to reduce the rate of warming over the next few decades.
And that importance could grow if we are successful in reducing carbon dioxide emissions from the burning of fossil fuels. In that scenario, methane, from all of its various sources, could become the most important source of greenhouse gas emissions.
Acknowledgements
Thanks to Rob Greene at the Jet Propulsion Laboratory for offering an important correction on the EMIT images.
Thanks also to Steve Hamburg for increasing the accuracy of this essay in many places.
Sources
Basic information and the image of the methane molecule are from:
https://en.wikipedia.org/wiki/Methane
https://en.wikipedia.org/wiki/Atmospheric_methane
https://commons.wikimedia.org/wiki/File:Methane-3D-space-filling.svg
An article on the use of methane to produce plastics is here:
https://www.scientificamerican.com/article/chemistry-may-yield-lucrative-use-for-wasted-methane/
Source for image of relative contribution to cumulative global warming by 4 groups of greenhouse gases is from:
https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing
Image of change in carbon dioxide concentrations over 800,000 years is from
https://climate.nasa.gov/vital-signs/carbon-dioxide/
and for methane is from:
https://earthobservatory.nasa.gov/images/87681/a-global-view-of-methane
Enhanced axis titles added by author
Data on global annual sources and sinks for methane are from:
Steve Hamburg's comments and results are drawn from:
The PermianMAP site is:
https://www.permianmap.org/
General information on the Permian Basin is here:
https://en.wikipedia.org/wiki/Permian_Basin_(North_America)
Information on the four remote sensing initiatives can be found on their websites by clicking on the names in the table.
The prism image is from:
https://spaceplace.nasa.gov/blue-sky/en/
The imaging spectrometer and methane plume images are from the Jet Propulsion Lab and can be found here:
https://www.nasa.gov/feature/jpl/methane-super-emitters-mapped-by-nasa-s-new-earth-space-mission
Source for data on distribution of human contributions to the methane budget is from:
Information on the use of landfill gas for energy can be found here:
https://www.epa.gov/lmop/benefits-landfill-gas-energy-projects
One source on reducing emissions from enteric fermentation is: