Researchers nail down the long-sought source of ocean methane

From the MASSACHUSETTS INSTITUTE OF TECHNOLOGY and the “settled science” department.

An abundant enzyme in marine microbes may be responsible for production of the greenhouse gas

CAMBRIDGE, MA — Industrial and agricultural activities produce large amounts of methane, a greenhouse gas that contributes to global warming. Many bacteria also produce methane as a byproduct of their metabolism. Some of this naturally released methane comes from the ocean, a phenomenon that has long puzzled scientists because there are no known methane-producing organisms living near the ocean’s surface.

A team of researchers from MIT and the University of Illinois at Urbana-Champaign has made a discovery that could help to answer this “ocean methane paradox.” First, they identified the structure of an enzyme that can produce a compound that is known to be converted to methane. Then, they used that information to show that this enzyme exists in some of the most abundant marine microbes. They believe that this compound is likely the source of methane gas being released into the atmosphere above the ocean.

Ocean-produced methane represents around 4 percent of the total that’s discharged into the atmosphere, and a better understanding of where this methane is coming from could help scientists better account for its role in climate change, the researchers say.

“Understanding the global carbon cycle is really important, especially when talking about climate change,” says Catherine Drennan, an MIT professor of chemistry and biology and Howard Hughes Medical Institute Investigator. “Where is methane really coming from? How is it being used? Understanding nature’s flux is important information to have in all of those discussions.”

Drennan and Wilfred van der Donk, a professor of chemistry at the University of Illinois at Urbana-Champaign, are the senior authors of the paper, which appears in the Dec. 7 online edition of Science. Lead authors are David Born, a graduate student at MIT and Harvard University, and Emily Ulrich, a graduate student at the University of Illinois at Urbana-Champaign.

Solving the mystery

Many bacteria produce methane as a byproduct of their metabolism, but most of these bacteria live in oxygen-poor environments such as the deep ocean or the digestive tract of animals — not near the ocean’s surface.

Several years ago, van der Donk and University of Illinois colleague William Metcalf found a possible clue to the mystery of ocean methane: They discovered a microbial enzyme that produces a compound called methylphosphonate, which can become methane when a phosphate molecule is cleaved from it. This enzyme was found in a microbe called Nitrosopumilus maritimus, which lives near the ocean surface, but the enzyme was not readily identified in other ocean microbes as one would have expected it to be.

Van der Donk’s team knew the genetic sequence of the enzyme, known as methylphosphonate synthase (MPnS), which allowed them to search for other versions of it in the genomes of other microbes. However, every time they found a potential match, the enzyme turned out to be a related enzyme called hydroxyethylphosphonate dioxygenase (HEPD), which generates a product that is very similar to methylphosphonate but cannot be cleaved to produce methane.

Methylphosphonate Molecular FormulaCH3O3P Average mass 94.008
Monoisotopic mass 93.983078

Van der Donk asked Drennan, an expert in determining chemical structures of proteins, if she could try to reveal the structure of MPnS, in hopes that it would help them find more variants of the enzyme in other bacteria.

To find the structure, the MIT team used X-ray crystallography, which they performed in a special chamber with no oxygen. They knew that the enzyme requires oxygen to catalyze the production of methylphosphonate, so by eliminating oxygen they were able to get snapshots of the enzyme as it bound to the necessary reaction partners but before it performed the reaction.

The researchers compared the crystallography data from MPnS with the related HEPD enzyme and found one small but critical difference. In the active site of both enzymes (the part of the protein that catalyzes chemical reactions), there is an amino acid called glutamine. In MPnS, this glutamine molecule binds to iron, a necessary cofactor for the production of methylphosphonate. The glutamine is fixed in an iron-binding orientation by the bulky amino acid isoleucine, which is directly below the glutamine in MPnS. However, in HEPD, the isoleucine is replaced by glycine, and the glutamine is free to rearrange so that it is no longer bound to iron.

“We were looking for differences that would lead to different products, and that was the only difference that we saw,” Born says. Furthermore, the researchers found that changing the glycine in HEPD to isoleucine was sufficient to convert the enzyme to an MPnS.

An abundant enzyme

By searching databases of genetic sequences from thousands of microbes, the researchers found hundreds of enzymes with the same structural configuration seen in their original MPnS enzyme. Furthermore, all of these were found in microbes that live in the ocean, and one was found in a strain of an extremely abundant ocean microbe known as Pelagibacter ubique.

It is still unknown what function this enzyme and its product serve in ocean bacteria. Methylphosphonates are believed to be incorporated into fatty molecules called phosphonolipids, which are similar to the phospholipids that make up cell membranes.

“The function of these phosphonolipids is not well-established, although they’ve been known to be around for decades. That’s a really interesting question to ask,” Born says. “Now we know they’re being produced in large quantities, especially in the ocean, but we don’t actually know what they do or how they benefit the organism at all.”

Another key question is how the production of methane by these organisms is influenced by environmental conditions in the ocean, including temperature and pollution such as fertilizer runoff.

“We know that methylphosphonate cleavage occurs when microbes are starved for phosphorus, but we need to figure out what nutrients are connected to this, and how is that connected to the pH of the ocean, and how is it connected to temperature of the ocean,” Drennan says. “We need all of that information to be able to think about what we’re doing, so we can make intelligent decisions about protecting the oceans.”

###

Note by Anthony: While the MIT finding is interesting, it is not the first. It was first proposed as the source of methane back in 2012: http://science.sciencemag.org/content/337/6098/1104

Synthesis of Methylphosphonic Acid by Marine Microbes: A Source for Methane in the Aerobic Ocean

Abstract

Relative to the atmosphere, much of the aerobic ocean is supersaturated with methane; however, the source of this important greenhouse gas remains enigmatic. Catabolism of methylphosphonic acid by phosphorus-starved marine microbes, with concomitant release of methane, has been suggested to explain this phenomenon, yet methylphosphonate is not a known natural product, nor has it been detected in natural systems. Further, its synthesis from known natural products would require unknown biochemistry. Here we show that the marine archaeon Nitrosopumilus maritimus encodes a pathway for methylphosphonate biosynthesis and that it produces cell-associated methylphosphonate esters. The abundance of a key gene in this pathway in metagenomic data sets suggests that methylphosphonate biosynthesis is relatively common in marine microbes, providing a plausible explanation for the methane paradox.

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71 thoughts on “Researchers nail down the long-sought source of ocean methane

  1. “Ocean-produced methane represents around 4 percent of the total that’s discharged into the atmosphere”

    ..doesn’t pass the sniff test……it has to be much higher than that..methane-oxidation-dependent denitrification happens in all substrates

    • I wonder if the thought ever occurs to the authors of these carbon fad papers that they are destined for the trash bin of history.

      • Yes, the knowledge is generally useful, so I picked the wrong study to cast off with the superfluous. I just think there will be a time when nobody cares too much about present day “carbon pollution” sources.

    • Well, it has a finite effect, it’s just very small. Even doubling or tripling its atmospheric concentration will have little effect on the total GHG effect and the average surface temperature.

    • Depends what you want to call significant. Here are the values I get with Modtran, full bore, alternately zeroing out the “major” greenhouse gasses vs their default values: Water, 90.84 W/m2; CO2, 31.18; Tropical surface ozone, 6.21; stratospheric ozone, 4.1; methane, 2.23.

      • Dan, thanks for the link. Busy right now, but read it a couple times and thinking. I’ve been too cheap to rent spetracalc so work with modtran. My modtran work confirms that CO2 absorption is entirely thermalized up to about 1km, where you begin to see a bite out of the Planck curve in the CO2 bands looking down. The “first bite” altitude for water is higher, about 2 km.

        I’m also intrigued with the notion of human water being more important than CO2.

  2. A radiant greenhouse effect caused by gases with LWIR absorption bands has not been observed anywhere in the solar system. The radiant greenhouse effect is science fiction. There is no real evidence that adding methane to the atmosphere contributes to global warming.

    If marine microbes are bad for the environment then lets go ahead and get rid of them by sanatizing the oceans. How much would it cost?

    • “How much would it cost?”

      Sanitizing the oceans to rid them of natural microbes would cause the whole world’s bio-structure to collapse.

      The cost would be “LIFE”

    • willhaas,

      A radiant greenhouse effect is not created by a light filter which is reducing light energy to the object warmed by the energy stream.

      Green house gases are the ones responsible for the 20% of otherwise available warming firelight from the sun, never entering into our Earth physical and by extension, mathematical systems.

      If it were possible there would be test questions in schools saying ”How much more light leaves the planet when the green house gases cause 1% to never reach it?

      B)How much more light leaves the planet when they cause 5% to never reach it?

      C)How much more leaves each time 15% never reaches Earth?

      These would be completely legitimate test questions since the Magic Gas Barking Brigade claim the Green House Gases warm the planet by 33 degrees.

      The entire atmosphere’s compression warming is 33 degrees.

      As a matter of fact one of the other absurd claims made by Magic Gas frauds is that their models can calculate the temperatures of gases in an unusual way.

      What’s that unusual method? Usage of only Stefan-Boltzmann processing in allegedly ‘calculating’ the temperatures of compressible phase matter – gases are compressible fluids.

      Stefan Boltzmann math process doesn’t include a feature or in math parlance, a function, for accounting this 33 degree warming for our global atmosphere.

      James Hansen once said ”These government computers are so fast, you have no idea what they can do… they’re nitrogen cooled, you know – and people just have no idea what we can do with these things…” in dismissing someone questioning him in a public appearance on video.

      What he was talking about – one of the several cons he ran while scamming grants on government computers, was his claim to be able to calculate the temperatures of gases in an odd way.

      We know the correct way to calculate the temperature of the global atmosphere, because we etched it into stone when the entire scientific world adopted the regulatory and physical standard called the

      International Standard Atmosphere.

      The calculations leading to the values of the International Standard atmosphere are known to be accurate, because ultimately it’s values influence the calibration of almost every instrument man uses that measures heat, as well as governing liability of everything that creates it.

      These processes include the process called discovery of the hydrostatic condition, which – immediately translates to density, in pressure.

      Gases have this intrinsically variant density relationship which must be accounted. Stefan-Botzmann-only mathematical processing doesn’t come up with the right answer for our global atmosphere.

      Their answer
      is 33 degrees short.

      Precisely and specifically because they do not process gas/atmospheric temperatures, using the gas laws that describe this. There is originally the Pressure Law, but later all four major gas laws relating fundamental matter-energy relationships were abridged into the modern variant of their expression, the Ideal Gas Law.

      The Ideal Gas Law governs temperatures of gases and compressible phase fluids by accounting and chronicling the relationships between volume, pressure, temperature, and density, and without it’s proper usage in processing atmospheric temperature,
      there occurs a 33 degree shortfall, which is precisely the measure of the alleged green house effect.

      Early scientists referred to compression warming as the green house effect,
      because a real greenhouse limits convection.

      This limiting of convection naturally increases conduction warming. Since nearly all atmospheric warming of your skin, the surface and it’s associated features is also conduction warming,

      early scientists in the various fields would be happy with this relationship description. I was taught that in school as a child as was pretty much everyone else who inquired into atmospheric sciences.

      However the Gas Law contains another much more damaging insult to the so-called radiative green house gas warming scheme, which claims addition of CO2, warms a mix of air it’s combined into.

      The second part of the Gas Law contains a Chart known as the chart of Gas Energy Constants: which is how much energy is held per average mole of many gases, and including air.

      CO2 has a lower energy constant than Air does in the Chart of Gas Constants. This is a matter of literally, the Gas Law written to describe – mathematically – what must happen in physics when these two are mixed – mandates addition of CO2 to Air cool it.

      This is why you never see anyone who believes the atmosphere is a heater, knowing anything about Gas Laws, claiming ”there are so many” – and constantly espousing claims that would make a welder laugh regarding gases and their temperatures.

      The first thing to ask anyone explaining to you about our ‘Changing Climate’ is if they think the atmosphere warms the planet. Ask them if they’ve ever heard of another cold nitrogen bath conduction chilling a light warmed object, warming it.

      Ask them why their Church, can’t calculate the temperature of the Atmosphere properly and attain the same temperature attained in solving of our International Standard Atmosphere.

      There is yet another rebuke to the Climate is Changing movement. The International Standard Atmosphere was adopted as a physical and regulatory standard after it’s existence was well documented for fifty years before that time, nearly a hundred years ago, around 1920, a hundred years ago.

      The International Standard Atmospheric descriptions have never changed, since that time, because the global climate is extremely stable and has been for the past 150 years, to the point that we still calibrate our aircraft, aerospace, and all heat producing equipment manufactured globally, against the Standard Atmosphere’s control of all our instruments.

      If climate were actually changing every Air Conditioner’s, Welder’s, Pilot’s, Sailor’s, and Engineer’s formal education would contain sections and chapters on how the Atmosphere is varying, with ”our changing climate.”

      No such sections exist in any formal Engineering mathematics classes because of the fact the governing Standard Atmosphere is still very much unchanged.

      In fact the U.S. Standard Atmosphere extended that International Standard out several thousand more feet than the International Standard, in 1976.

      Signed, one of the early N.A.S.A. Fan Club kids,

      Nathaniel.

      • I have always pointed out that if CO2 really affected climate that the increase in CO2 over the past 30 years would have caused at least a measurelble increase in the dry lapse rate in the troposphere. Since 1974 there have been what amounts to updates to the Standard Atmosphere but they have not included any changes to the dry lapse rate in the troposphere.

    • Careful. Methane-producing microbes are virtually everywhere: in the guts of animals, forests, oceans, lakes, etc. We might be able to afford to sanitize the oceans, but sanitizing the entire planet would probably break the bank.

      • According to the AGW conjecture the primary greenhouse gas is really H2O and not CO2 or CH4. So far there is no effort underway to remove H2O from the atmosphere or to keep it from reintering the atmosphere either. For example in the city where I live H2O becomes so concentrated in the atmosphere that it often condenses out as a liquid. The city provides an underground network of pipes to channel this liquid greenhouse gas away. All the city does is dump this liquid greenhouse gas outside of the city limits where it is allowed to evaporate back into the atmosphere. The pool of liquid greenhouse gas has grown so large that it can be seen from space and it even provides an environment where flesh eating organisims thrive. The EPA has made no attempt to force the city to clean up the mess that they have made. If the so called greenhouse gases are bad then the EPA should shutdown all sources of greenhouse gases. People should be forbiden to make use of any goods and services that make use of fossil fuels because it is their money that keeps the fossil fuel companies in business. People should not be allowed to consume or posses or make use of anything that involves hydrocarbon compounds, H2O, O2, N2, or H2 because it might result in so called greenhouse gases entering the atmosphere.

  3. Until they can explain why atmospheric CH4 stopped increasing in the late 90s and then restarted in mid 2006 AND why the incremental CH4 since then has been mostly biogenic in origin (rather than thermogenic) AND why the start of the increase in 2006 was essentially synchronous latitudinally despite significant “offsets” in values from south to north, they are not really helping with our understanding of atmospheric methane levels. (I can provide the back-up data to my three points later tomorrow, if anyone is interested, though I think that they are all well known.)

      • Patrick,
        You obviously have become used to having servants.
        It’s far more convenient than doing anything for yourself.
        Do you also have an iron lung?

      • “toorightmate December 7, 2017 at 4:30 pm”

        Not sure what your issue is with my post anyway…I do my own research and form my own conclusions. It is however good to see other peoples work when they offer to share.

        I don’t have an iron lung but I do have a stent. I needed that inserted by someone else to help me stay alive.

      • Patrick,

        Thank you for your interest. I shall post some info at the bottom of the thread shortly. I hope it is useful, though I don’t have the answers, only the observations!

    • I’m with Jim Ross on this one. I find this study interesting, but I’m not sure that it contributes much to the big picture. The known biochemical and inorganic fluxes of methane are very large and poorly quantified/explained. Tinkering around the edges with some interesting new mechanisms doesn’t really change anything.

  4. “…so we can make intelligent decisions about protecting the oceans.” Hoo-boy. Hubris much? Whatever man’s effect on the oceans is, it is tiny. Worrying about what ocean microbes are doing as a result of man’s activities is absurd, just as worrying about methane is, and CO2. But hey, I guess these “scientists” have to pay the bills somehow. Might be nice if they could do something actually useful though.

    • Hubris? Well, yes, now that you mention it, there is a bit of water in the oceans. (Google says 1.332×10**9 cubic kilometers) so, it may take a few weeks to get all the nasty Methane generating bacteria out. But I’m confident that the engineers can handle that.

  5. WHAAAT???

    You mean the SCIENCE WASN’T SETTLED??!!

    How Could that be? I mean these people have computers and the internet and their very own blog pages. What the hell is going on?

    /sarc? – Not just yet, lots more to come given the antics of the Climate Clowns.

      • Perhaps this study will lead to future development of methane generation by microbes for power plant fuel.

        What if you farmed them in controlled containers? Is there sufficient CH4 production in concentrating these marine in vitro to pursue it as a source of energy?

      • @Pop Piasa:

        In this country, sewage treatment plants and agricultural ‘factory farms’ are beginning to harvest methane from sewage. In some other countries (other than the US), ‘biogas generators’ take the place of septic tanks. Many families use the ‘biogas’ as fuel for cooking. It’s a great idea.

    • Maybe not get rid of them, they just need to control them.
      Along with the weather, the distribution of wealth, and the public consensus.

  6. Those 40,000 recently discovered undersea volcanoes should be putting out quite a lot of Methane, CO2 and other so-called “Greenhouse Gases”. You can make intelligent decisions about the oceans, by just leaving them alone to get on with their job, safe from Eco-Loon interventions. “Ocean! Thou mighty monster!”.

    • All those under sea volcanoes need to be caped so that they no longer emmit greenhouse gases. How much would it cost to cap one under sea volcano?

      • let’s say 1 billion each. 40,000 billions. 1,000 billion a year for 40 years’ work.
        Leave it to me, i’ll manage. Trust me.

  7. By far the largest contribution to the Earth’s so called greenhouse gases that the oceans make is not CH4 but rather H2O. Warming ocean currents also add CO2 to the atmosphere because as the water warms it cannot hold as much CO2 as the colder waters can. If the so called greenhouse gases are bad then maybe all bodies of water should be covered with plastic so that H2O and CO2 are not allowed to enter the atmosphere.

    Where I live the concentration of greenhouse gas becomes so high that some of it condenses out and falls to the ground as a liquid. The city knows about this problem and has installed a network of underground pipes to channel the liquid away. All the city does with the liquid is dump it outside of the city limits where it is allowed to evaporate back into the atmosphere. The pool of liquid is enormous and can even be seen from space. The EPA needs of step in and force the city to completely clean up the big mess they have made and to permanently get rid of the liquid greenhouse gas.

    Then there is the gas in the Earth’s that holds the most heat energy and that is largely responsible for the Earth’s surface being as warm as it is. The gas in N2. Getting rid of all the N2 in the Earth’s atmosphere will definitely cause cooling.

      • The best way to deal with it, is to expose it to very high temperature. It then separate into oxygen and another gas you just need to vent in the atmosphere for it to quickly leave the planet. Problem solved.

      • H2O is really DiHydrogenMonoOxide of DHMO for short so it is alreasy an oxide and cannot be burned. There is not enough space in salt mines to put it and it would end up desolving some of the salt. H2O can still evaporate from brine. Through electrolis H2O can be turned into O2 and H2 but there is always the change they will again react with each other to form H2O again. Then there is the idea of turning H2 into He atoms as happens in fussion bombs. Another approach would be to keep all H2O on the Earth
        s surface at a temperature less then -40 degrees F so that it does not sublime into the atmosphere.

      • “H2O is really DiHydrogenMonoOxide of DHMO for short”

        That’s nothing!

        Some of it is of course found as Hydroxylic Acid, when oxygenated the most corrosive substance in the known universe, and responsible for untold billions of £/$/€ of damage to structures and vehicles every year.

  8. Well they certainly went into TMI territory explaining how they found the enzyme and it’s potential imitators. What wasn’t explained is the process/circumstances by which the cleaving takes place. That’s kinda important, no?

  9. Do these scientists have any idea how much MONEY an enzyme that makes Methane is worth.

    Many $billions of dollars.

    Hey, if you can produce Methane (which is what 98% of natural gas is made up of), then you are manufacturing an awesome fossil fuel and an energy source.

    • Nothing new. This has been done for years in Eurpe to produce Politically Correct Natural Gas. The problem is to do it economically.

    • “Hey, if you can produce Methane (which is what 98% of natural gas is made up of), then you are manufacturing an awesome fossil fuel and an energy source.”

      I find baked beans work very well myself…

  10. So the microbes do not make methane if they have enough phosphorus?? Yet we are taking phosphorus out of most fertilizers because someone decided it is a major pollution problem. I cannot believe that at least some of the methane from the deep oceans does not make it to the surface by upwelling or thermal vent force water to the surface.

  11. “Where I live the concentration of greenhouse gas becomes so high that some of it condenses out and falls to the ground as a liquid”

    This time of the year, where I live the concentration of greenhouse gas becomes so high that some of it condenses out and falls to the ground as a solid. The city just pushes it out the way into big piles. It does eventually (often after several months) turn to a liquid and run off into the big puddle of liquid to our north where it eventually evaporates and starts the whole cycle again. I think the city needs to look into some sort of Solid Greenhouse Gas Sequestration System.

    • Great idea. I was told there already is a massive pile of this south of South, and also in Greenland, so we just have to dump it there.

    • It is rather the other way round: if nature produce it, eventually nature will use and even need it. Like oxygen, a massive garbage until some living organisms managed to take advantage, so much so that they cannot live without it anymore

  12. Bunk. It is methane production by methanogens in microenvironments (i.e. clumps of crap) in the uppermost layers of the ocean.

    The methane concentration maxima occur at the pycnocline, suggesting that the maxima are supported by methanogenesis in suspended particles that accumulate at these depths. Particle incubation experiments show that methane production may occur in these microenvironments. The lack of a diurnal signal implies that methane production and consumption in the ocean is independent of day-night cycles such as photosynthesis, grazing and vertical migration of zooplankton.

    http://onlinelibrary.wiley.com/doi/10.1029/1999GB001209/full

  13. Pretending that this is new is just graduate research hype. The marine methane ‘mystery’ has been explained biologically since a 2008 paper in NatGeo. This is but a small addendum to the literature. Only took four hours to do a full lit search and realize how this was previously experimentally shown.


  14. David Attenborough explains in simple terms, the origin of methane in the Gulf of Mexico:
    “chemical reactions in the seafloor”, a.k.a.,
    serpentinisisation

    The methane on Titan is attributed to the same rock/water reactions that we observe here on Earth, because, after all, the physical properties responsible for chemical reactions are universal.

    This is why methanotrophs–gas and oil guzzling microbes–have successfully infested the planet from pole to pole for eons without ever running short of the vital supply of so-called “fossil fuels.”

  15. Is it possible all the pollution humans dump into the oceans is feeding some of these microbes? That might be a cause of a small rise in methane. Or, it might not even be detectable.

    • Thanks for asking, Richard. This is certainly the case (pollution feeding microbes), particularly nutrients from farming runoff. We see vast plumes of phytoplankton in the Gulf from the Mississippi River discharging nutrient-rich water, and this is observed globally. The most important nutrients are phosphorus and nitrogen, and pollution also contributes essential micronutrients such as nickel.

  16. a better understanding of where this methane is coming from could help scientists better account for its role in climate change

    Or they could find that it plays essentially zero role in climate change no matter where it is coming from. Of course then they would lose a huge funding source but sometimes reality hurts.

  17. I mentioned above about three issues with respect to atmospheric methane. These issues seem to me to be the “big questions” and I have been unable to locate a meaningful and convincing explanation (i.e. anything more than simply arm waving). In that context, there is actually quite a helpful summary published by NOAA and I have included some selected quotes from it in the text below. The link to the summary:
    https://www.climate.gov/news-features/understanding-climate/after-2000-era-plateau-global-methane-levels-hitting-new-highs

    Regarding my first point, there is no dispute about what has happened. As they state in the summary: “Strangely, though, global methane levels “flat lined” from 1999 to 2006. The plateau didn’t last, however, and in recent years, global methane levels have been hitting new highs.” Here is their plot (note units: parts per billion):

    I am not sure if the above plot is based on some sort of global averaging, so here I show Barrow (Alaska), Mauna Loa and South Pole individually:

    Clearly, the trend is the same at all latitudes. I’ll return to the matter of offsets later. So, why did the growth rate diminish to zero for a time? Here’s NOAA’s version: “The leading hypothesis is that industrialized countries, including the United States, got better control of “fugitive” methane emissions, which escape during drilling and pumping of oil and natural gas. The hunt for an explanation is complicated by the fact that experts aren’t even 100% sure that the atmospheric lifetime of methane is constant. The lifetime of a methane molecule released into the air is mostly controlled by reactions with the atmosphere’s primary oxidizing agent: the hydroxyl radical (OH).” In summary, then: we don’t know.

    So what about the increase in growth after 2006?
    “Possibly the most important clue: air samples collected at different latitudes around the world show that the amount of methane carrying carbon-13—a rare, heavy isotope of carbon—has dropped significantly since 2007. That drop casts doubt on one of the first explanations experts considered for the post-2007 rise: an increase in methane emitted from fossil fuels, including “fugitive” methane gas escaping during oil and natural gas drilling. Instead, the chemical fingerprints point toward agricultural and wetland emissions from the tropics.” Damn, we can’t blame the oil industry. As for the reason for the increase in biological activity there is some speculation trying to link it to ENSO (El Niño-Southern Oscillation), but my summary is, again: we don’t know.

    The following NOAA plot shows the “uptick” in methane growth (annual variation not shown for clarity) as well as the decreasing δ13C-CH4 on a common datum for different latitudes. This avoids any need to address the offsets, but it does highlight very well the globally synchronous nature of the change in growth rate.

    This I find interesting in the context of CO2 growth, even if it is not directly applicable. We often hear that the (small) offsets in CO2 levels at different latitudes can be explained by delays in emissions spreading around the globe (especially a delay in crossing the ITCZ). My view is that such an explanation is difficult if not impossible to sustain beyond a matter of months if you look at the δ13C-CO2 trends (which also demonstrate the globally synchronous nature of changes in trend). In the case of methane growth, we have very clear evidence of significant latitudinal offsets which are independent from the virtually simultaneous changes in growth rate across all latitudes.

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