Do Earthworms Contribute to Global Warming?

Dr. Clive Edwards
Dr. Clive Edwards.
(Image courtesy of The Ohio State University)

According to Dr. Clive Edwards, the answer is “no” – or at least there simply isn’t enough evidence to suggest that they do.

I can clearly remember back to when I first caught wind of the news stories claiming that vermicomposting was bad for the environment (in summer of 2007). Being the vermicomposting fanatic and advocate that I am, it was like a slap in the face. I immediately felt defensive and angry.
‘How could this possibly be??’
The initial anger gave way to skepticism regarding the validity of the research. All stories pointed back to one source – The Open University, in the UK – and I couldn’t figure out where (if anywhere) the actual research results were published. Surely, with all this media coverage this must have been conducted by eminent scientists and published in a peer-reviewed journal, right?

Despite my feelings of doubt however, I decided to keep a totally open mind (and a closed mouth) until I learned more. I hoped that someone would be able to point me in the direction of the original research, so I made an effort to follow the story (and ensuing dialogue) around the blogosphere but it seemed that everyone was relying solely on the sources found in the popular media.

Well, like all breaking news, the ‘worms are killing the planet’ headlines gradually disappeared, and the entire issue basically slipped off of my radar screen – becoming an unsolved mystery relegated to my mental back burner, where it collected dust with countless other topics that were of interest at one time or another. That is until earlier this week, when I caught a blurb on Twitter containing some VERY intriguing news from vermicomposting professional, Brenda Lotito. It read “Its official! Commentary from Dr. Clive Edwards, Ohio State University..Vermicomposting does NOT harm the environment!”

Needless to say, I immediately contacted Brenda to find out the source of this revelation, and she pointed me in the direction of an article published in the most recent issue (Dec 2008) of BioCycle.

I don’t think I could imagine a more satisfying way to see this ‘mystery’ solved, than to learn that Dr. Edwards (world renowned vermicomposting researcher, email friend and mentor) would be the one to get to the bottom of the issue and come back with such an excellent response.

For those of you unfamiliar with ALL of this – in a nutshell, Dr. Jim Fredrickson from The Open University claimed (in a media interview) that vermicomposting poses a significant global warming threat due to the release of large quantities of nitrous oxide (N2O) gas, which is 20 times more potent as a greenhouse gas than methane, and almost 300 times as potent as CO2 (the gas that gets most of the attention – understandably, since it is by far the biggest threat).

I found the claim particularly interesting since, aside from being a passionate vermicomposter, I was actually involved in research examining greenhouse emissions from composting during my grad school years, and was in close contact with others studying N2O emissions from other natural and human-influenced sources. This is actually a big part of why I wanted get a hold of the literature that backed up the claim – I was curious to see how exactly the Open University researchers conducted their experiments, how the numbers stacked up against other well-known N20 sources (such as soil), and also just generally, how significant all this was in the grand scheme of things.

As it turns out, there was indeed some research officially reported by Dr. Fredrickson (and his colleagues) back in ’03 and ’05, which according to Dr. Edwards had “poor experimental designs, inadequate replication and unsatisfactory control of environmental conditions in the vermicomposting beds” (BioCycle reference listed at end of this post). Apart from the sloppy science involved, Edwards also points out that (according to ‘Trends in Greenhouse Gaseous Emissions’, 2006), ALL forms of composting only contribute 0.5% to the total global greenhouse gas emissions!

One of the major issues with the research, as claimed by Edwards, was the lack consideration given to moisture content, which can be a very important factor affecting N20 emissions.

Another serious flaw came in the form of a claim by Fredrickson (to support his own assertions) that German scientists had discovered that worms were responsible for 1/3 of the N20 released when present in a composting system. As Edwards points out, the studies being referred to were actually examining worms in garden soil systems (small laboratory ones at that) NOT vermicomposting beds!

Edwards finishes the article beautifully by referring to multiple studies that have suggested that worms either do not affect N20 emissions at all, or in fact seem to bring about a decrease in emissions of this greenhouse gas!

Here is a quote from the very end of the article (again, reference to follow) that provides a nice overall assessment of the situation:

“While there will be N20 emissions from all these [composting] sources, there is no justification for suggesting that environmentally-friendly and energy-efficient systems for producing vermicomposts and composts should be restricted because of their potential to produce greenhouse gases. The global production of nitrogenous greenhouse gases in agriculture should be compared from all sources before vermicomposting is publicly condemned in such a sensational way.”

As Homer Simpson would say (and thus at the risk of sounding a tad unprofessional):


Global worming does NOT promote global warming!

Edwards, C.E. 2008. Can earthworms harm the planet? BioCycle 49, 12: 53-54.

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  1. I like this part: ‘The initial anger gave way to skepticism regarding the validity of the research.’ – Typically scientific approach!
    But I am with you. I thought plastic bins emit N2O…

    • Bentley
    • January 11, 2009

    Hehe – yeah I tried to keep a scientific perspective, rather than letting my emotions get the better of me!

    I think you can still get some N20 release from these systems – but the argument (presented by Dr. Edwards) is that it is pretty insignificant – certainly not enough to warrant the grand claims that were being made!

    • Rich
    • January 11, 2009

    Also, the analysis only makes sense if you consider the alternative ways in which the organic waste would be decomposed.

    • Patricia
    • January 11, 2009

    Aside from the scientific side, haven’t worms been around for millions of years without complaints? Global worming has been an issue for how long?

    • Kate
    • January 11, 2009

    Yay! I love it when stuff like that happens! How can I prevent my worm bin from emitting N2O? You said something about moisture content….if everything is well balanced, should it be ok?

    Just out of interest, Bentley, what education background do you have in these areas? Bio? Ecology? It would be quite cool to study this sort of stuff as well as have it as a hobby. What sort of degrees would be applicable?

  2. Global warming is a liberal myth. The closest trend in earth’s temperature is sun spots, not human intervention.

    • Saint Splattergut
    • January 11, 2009

    Do Earthworms Contribute to Global Warming?

    Well, if they do… guess what. Too effing bad. Because they’ve already been around for a while, in ur s0il m322ing uP ur 34RtH!!!!!!!!!


    • Angie Hill
    • January 12, 2009

    I’m a Master Composter in the UK, and was also dismayed to hear that vermiculture could seriously contribute to global warming. I feel such “research” is yet another bid by a few hardcore cynics, to discredit the “greener”, more holistic, and sustainable methods of horticulture. Let’s face it, the more popular such composting methods become, fewer agrochemicals and inorganic fertilizers will be needed. Not wishing to offend, but every time humankind breaks wind, another shot of methane hits the atmosphere…, we humans are as much to blame as anything else. Here’s to global worming I say!

    • Dwayne
    • January 12, 2009

    Good post Bentley!

    • Bentley
    • January 12, 2009

    Wow – guess this is a hot topic!!
    Thanks everyone for chiming in. I’m going to respond to everyone in this post and will bold each person’s name.

    Rich – could you elaborate – I’m not sure I follow. Which ‘analysis’ only makes sense? Thks

    Patricia – Spoken like a true ‘worm-head’ you said “global worming’ when I think you meant ‘global warming’ – haha (you’ll probably relate to my next blog post). As a response to your question, while YES worms have been doing their thing for countless years, the issue is supposed to be with large-scale, man-made vermicomposting systems – although I would certainly be interested to find out how much N2O gets released from a big pile of manure full of composting worms, vs one just sitting there on its own.

    Kate – I definitely wouldn’t worry about it! I’m sure you are doing just fine! hehe
    As for my educational background it is pretty well all over the place. I started with a biology degree mainly focused on aquatic ecology. I then went back to school for some extra (non-mandatory) undergrad courses in soil and plant biology. I then made it about 3/4 of the way through a masters program (long story – haha) in soil science, with my main project focused on ammonia and greenhouse gas emissions from composting and vermicomposting. The people to talk to would be those in soil and environmental science departments at the universities/colleges you are interested in. Go to OSU and study at the soil ecology lab with Dr. Edwards if you definitely want to immerse yourself in vermicomposting research.

    Bill – I must admit that I was tempted to simply delete your comment since I didn’t feel it added to the conversation, but thankfully I got my ego out of the way and realized this is all about freedom of speech. I respectfully disagree with your opinion wholeheartedly based on the evidence now on the table, and more importantly on the fact that the vast majority of the world’s top scientists are in agreement about this. Sure, if there was a small handful of radical outsiders trying to convince the scientific community that would be one thing – but this literally IS the scientific community!

    Saint Splattergut (love the name – haha) – I think you are saying something similar to Patricia. Again, while yes they have been around doing their thing for a long time, I think the argument being made by Dr. Fredrickson is that the largescale human-operated vermicomposting systems are the concern. Presumably, if vermicomposting spreads and becomes mainstream, all these new systems will release so much N2O that we’ll all be doomed. Joking aside – human involvement is the key here. We are breeding these things more and more so it’s not just about the wild populations of worms out there emitting GHG’s. I do totally agree though – a lot more important things to focus on!!

    Angie – very well said! I agree wholeheartedly.

    Dwayne – thanks! Good to see you ’round these parts!

    • Rich A.
    • January 12, 2009

    “Global warming is a liberal myth.”

    Global warming is a scientific theory, backed up by growing evidence, that is the consensus of the world’s leading scientists.

    The difference between a liberal and a conservative is that when each wants to know if it will rain tomorrow, a liberal asks a weatherman and the conservative asks the person who wants to sell umbrellas.

    • Patricia
    • January 13, 2009

    And how often are weatherman right about the weather?

    • Jane
    • January 13, 2009

    The meteorologists (some of them are not “men”) are pretty accurate in my area. Sure, there is some “art” to predicting the weather, but that doesn’t invalidate the science.

    • Rich
    • January 13, 2009

    My weatherperson analogy clearly missed the mark. My point was that there is nothing “liberal” about the science of global warming.

    • Bentley
    • January 13, 2009

    What I don’t get is what being ‘liberal’ and ‘conservative’ has to do with this at all? Generalizations made about people of a certain political leaning takes us away from the issues of actual importance. I’m sure there are skeptics and supporters on both sides.

    P.S. You snuck in there just before me Rich

    • Kate
    • January 13, 2009

    Besides, scientists are specifically trained to eliminate bias in their conclusions. They would be the last people to let political views influence their data.

    • Patricia
    • January 13, 2009

    So if we all keep our worming projects on a small scale, since the study was geared towards large scale ventures, we don’t have anything to worry about other than if its better to be a liberal or conservative? I am going back to feeding my worms. Thanks Bentley.

    • Bentley
    • January 13, 2009

    We don’t have to limit the size of our projects. Whether big or small, vermicomposting systems are not going to ruin the environment.

    The original claim was that vermicomposting beds (namely, larger-scale, man-made systems) are significant emitters of N2O gas – significant enough in fact to warrant discouraging this type of composting.
    BUT Dr. Edwards illustrated that this conclusion was unfounded.

    So yes…time to go feed your worms!

    • Kevin Rayburn
    • August 23, 2009

    There is an error in your abstract of Dr. Clive’s article that makes the argument against vermicomposting even more ridiculous.

    You said that Dr. Clive Edwards said that .5 percent of Green House Gases come from all composting. Actually, it is .5 percent of 5.2 percent (N02 emissions), which means that composting only contributes .026 percent of GHGs! That is such a small number! Below is the exact quote from the article.

    “In the U.S. in 2006, 84 percent of greenhouse gas emissions were carbon dioxide (CO2), 7.8 percent were methane (CH4), and 5.2 percent were nitrous oxide (N2O). Of the N2O emissions, 72 percent came from managing agricultural crop residues, 3.9 percent from animal manures and 0.5 percent from all forms of composting, including vermicomposting (Trends in Greenhouse Gaseous Emissions, 2006).”

    5.2 X .005 = .026 %

    • Kevin
    • August 23, 2009

    Link to Dr. Clive Edwards Article:

    • Bentley
    • August 23, 2009

    Hi Kevin,
    Thanks for the correction and for the link to the article (I didn’t realize they had posted it for public viewing)!

  3. Hi composters !

    Congrats for this useful website I found when looking for some information about the red worms and the gas emissions they incur. My lil doubts concerns the range of CO2 emissions produced by the red worm in the composting process.
    Is there a minimum and maximum measure of CO2 produced by red worms when processing their food?
    Is that enough CO2 for my indoor tomatoes to grow up when sequestering CO2?
    Could it be in some way beneficent to add the CO2 produces in the vermicomposting process to indoor planting?

    A passionate beginner composter

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