Wrestling with methane metrics

The methane debate is more about politics, policy and value judgements than it is about science

In my previous article, I explained how there is much controversy about how methane should be compared to carbon dioxide in terms of global warming. The problem arises because methane is a powerful greenhouse gas but it lasts only a short time in the atmosphere. In contrast, carbon dioxide is a weak greenhouse gas but it lasts much longer. Also, there is a lot more carbon dioxide than methane released into the atmosphere.

Big problems arise when methane is shoe-horned into carbon dioxide equivalence. Here I will explain some of the problems.

First, many people will be surprised that this issue of carbon-dioxide equivalence and the associated controversy is not really about the science. Scientists understand the nonsense of trying to estimate how many apples it takes to equate to one orange, with the answer depending totally on the chosen measures. Similarly, scientists understand that methane has a totally different emission profile than carbon dioxide and there is no simple equivalence measure.

However, the general public together with policy makers and politicians like to keep things simple. They want to be able to add the two together regardless of the problems and flawed thinking this creates.

The internationally accepted way for reporting emissions back to the UNFCCC, which is where climate-change policy issues are decided, is to think of carbon dioxide as the big brother and methane as the little brother. Little brother has to fit in with big brother. Accordingly, methane is typically converted to units of carbon dioxide equivalence (CO2e) on a 100-year timeframe of global warming, with this denoted as the GWP100 effect.

In doing the calculations, the methodology looks forwards rather than backwards. It doesn’t matter what emissions might have occurred in the past. The only question being answered is how much warming over the next 100 years will be caused by the new emissions.

Given that specific question, and within the current limits of scientific knowledge, the GP100 metric gives correct answers. If you want another answer, then you also have to change the question.

When Government officials report that agriculture makes up almost half of New Zealand’s emissions, this is based on this 100-year assumption, although that caveat is almost always lost in media reporting. Similarly, if agriculture were to enter the Emission Trading Scheme as currently structured, then it would be using the GWP100 equivalence assumption that underpins that system.

I will use two examples to illustrate the importance of this assumption.

Some people are concerned about what will happen to the Greenland and Antarctic glaciers. If these glaciers melt, it will be over a period of many hundreds and possibly thousands of years. If they do melt, sea levels will rise many metres and mega-cities across the world will be drowned.  

If this occurs as a consequence of greenhouse gases, then it will be almost totally due to carbon dioxide that is piling up in the atmosphere. This is because much of the carbon dioxide released today will still be in the atmosphere in another 500 years. In contrast, the methane that is released in the next 50 years will all be gone, and hence is essentially irrelevant to that long-term situation.

The second example relates to a current focus on short-term temperatures with 2050 being a particular focus. We read continually in the media about the so-called challenge of keeping the accumulated global increase in temperature to less than 1.5 degrees C compared to pre-industrial 1850.

In a scientific framework, there is nothing special about 2050. But society likes targets that can be enunciated in simple terms. This 2050 target, linked to a pre-industrial 1850 baseline, is what climate-science politicians and lobbyists are focusing on. This is despite the pre-1950 component of the change almost certainly being largely natural and unrelated to human activities.

Given this target, combined with the scientific fact that it is impossible to reduce the ongoing temperature effects of past emissions of carbon dioxide, it makes sense to place significant emphasis on reducing global methane emissions. It could indeed be an important way to influence temperatures in 2050, albeit by in all likelihood less than 0.1 degree Centigrade at that time, even if undertaken globally.

The key take-home from these examples is that just like apples do not have an orange equivalence, so too it is important to not conflate issues of short-term versus long-term greenhouse gases.  There is no simple overarching metric for comparison.

Many and probably most climate scientists would agree with the above paragraph about not conflating short and long-life greenhouse gases. But alas, many politicians and lobbyists have no understanding.  

Accordingly, some climate scientists have stepped forward from analysing the climate itself to try and find alternative metrics that can be used in the policy framework where politicians and lobbyists work.

In understanding these alternative methane metrics, I often refer to the invisible methane cloud sourced from New Zealand’s pastoral animals. It is the current size of this invisible cloud that determines the current temperature effects of New Zealand’s historical pastoral emissions.

Think of this atmospheric cloud as being the atmospheric equivalent of a bath-tub effect with a tap running and the plug partly removed. Water flows in and water flows out. The stock of water in the bath will depend on how fast the taps is running and how fast the water is leaving down the plug hole.

With methane, scientists know that the flow of methane into the atmosphere from New Zealand ruminant animals is close to what it was 30 years ago.  As a consequence, and linked to the scientific knowledge that about eight percent of methane molecules decompose each year, an approximate balance in the atmospheric ‘bath tub’ has been reached and the atmospheric cloud of NZ pastoral-sourced methane is close to stable. Hence, this argument goes, New Zealand’s agriculturally-sourced methane is contributing to further global warming in a minimal way.

In contrast, with carbon dioxide only a small amount of carbon dioxide leaks out through the plug hole and the stock of carbon dioxide in the atmosphere keeps increasing each year. 

This insight, variously stated, underpins the GWP-star metric, written GWP*, which some people are now promoting vociferously. Whereas GWP100 looks forward at the effect of this year’s emissions, the GWP* metric focuses on the changes in emissions that have occurred compared to a historical period and hence, in relation to methane, on the change in size of the atmospheric-warming cloud.

The argument then goes that because the NZ-sourced atmospheric methane cloud is essentially stable, New Zealand farmers should not be charged for doing what they, or more particularly their animals, have been doing for a very long time.

Recall that earlier in this article I said that GWP100 metric provides an accurate measure of the 100-year warming effect of current emissions, with this effect being measured relative to if those emissions did not occur. In contrast, the GWP* metric answers a different question, which is whether or not the atmospheric methane cloud is increasing. Each is correct for the question that is answered.

Many people in NZ agriculture are very keen on GWP*. This is for the obvious reason that it leads towards a conclusion that any methane charges incurred by NZ agriculture should be minor.  

However, the GWP* metric gives a very different answer in situations where the atmospheric cloud is increasing from new emitting activities.  Accordingly, using this as a basis for emission charging leads to new emitters being charged heavily.

The principle of using past emissions to justify ongoing emissions is called ‘grandfathering’. It is the reverse of a key principle within the Paris Agreement that developed countries with current high emissions must carry the main burden of emission reduction.

Here, I will give just one of many examples of grandfathering effects.

Some eight years ago, I led an MFAT-funded dairy-development design team to Colombia. Although close to the equator, Colombia includes temperate lands between 2000 and more than 3000 metres altitude that is highly suitable for dairying. Also, the Colombian Government sees dairying as a wonderful alternative to growing cocaine. However, if the GWP* metric were to be used to assess greenhouse gas effects, then Colombian dairy developments would show up badly because they generate new emissions.

So, given these ethical issues, how do we move forward here in NZ, where pastoral-sourced food underpins so much of our export-led economy?

Once again, in this article I have only scratched the surface of multiple complex issues. Although I think there is a path forward for both NZ agriculture and NZ society, that must be another article.

So, my final take-home message from this article is that climate-change issues are indeed complex.  Also, much of the debate is ill-informed. It is like two warrior groups standing on either side of a wide gully shouting insults at each other, with each group accusing the other of being ignorant. Each warrior group can only hear itself.


About Keith Woodford

Keith Woodford is an independent consultant, based in New Zealand, who works internationally on agri-food systems and rural development projects. He holds honorary positions as Professor of Agri-Food Systems at Lincoln University, New Zealand, and as Senior Research Fellow at the Contemporary China Research Centre at Victoria University, Wellington.
This entry was posted in Dairy, greenhouse gases, sheep and beef farms, Uncategorized. Bookmark the permalink.

7 Responses to Wrestling with methane metrics

  1. Paul McGill says:

    Thanks Keith,
    There are a few flaws in this in my opinion.
    1) The interest of GWP* use by people here is not about ‘not having to do much on methane’ at all! It is about reflecting what is done, in a like for like way (fair & just with CO2 treatment). The argument you make is what some people like use to discredit using something that is actually comparative to what this is all about – temperature impact.
    2) You state GWP* is looking back & GWP100 looking forward. That’s not an accurate description at all!
    – GWP* factors in emissions over time. It’s the only way you can assess the climate (temperature) impact of short-lived GHGs, over the periods we are talking about <100yrs.
    – GWP100 looks at point in time emissions, as if they are a ‘pulse’ emission to calculate the Radiative Forcing (RF) of the GHG. Biogenic methane from pastoral food systems are not a pulse emissions.

    At a stable methane emission rate, there is a three fold difference in what GWP100 will calculate to what GWP* will. Only one is representative of the actual warming impact, and it is NOT GWP100.

    As per your Apples & Oranges analogy, GWP100 tries to make something that looks like a triangle, and represent it as a rectangle. It is a triangle!

    GWP* in some ways is less of a metric & more of a model. It models the impact on temperature of GHGs. This aligns to Paris agreement & our ‘split gas’ ZCA goals. Farmers get models, we use them for financial, biological, and environmental parts of our systems. Simple notions, especially when fatally wrong, is pointless.

    Yes, if emissions increase then GWP* will reflect that aggressively. As you would expect it too based on temperature impact. Again, GWP100 doesn’t do this well either. If you then put a ‘95% free allocation’ thing in place it is a massive future impact subsidy. HWEN is very much caught up in this. You are rewarded more for increasing, than decreasing emissions. Call it ‘Grandchilding’ if you want.

    The notion the GWP* is ‘grandfathering’ can’t be any different to how we treat all the past CO2 emission we aren’t looking at pricing. At least with methane we can stop & back out some of past warming by reducing emissions.
    Farmers work in the real world. GWP* is the real world. It reflects GHG emissions with surface temperature changes. That is reality and there are plenty of global customers wanting food is not adding additionally to warming as part of wider holistic outcomes. We can work do this. It is a point of difference that you can’t achieve by emission swapping with CO2 to produce lab meats, fermentation foods and alike.

    Sure, make the case about policy & politics. But don’t get the real science, ‘fair & just’ treatment & the ability to tell our customers what we are striving to do, confused with narratives that detract from the real reason for using something that works. It’s a lot more compelling than trying to hold on to something that is 30yrs old, not fit for purpose, and knowingly, never was.

    • Keith Woodford says:

      It is important to recognise that GWP and GWP* are built on precisely the same science. Both recognise that methane is a short life gas and that carbon dioxide is a long-life gas. So, they both follow the same science.

      The difference is that they address different questions.

      GWP100 addresses the question as to how much warming will occur during the next 100 years from a new emission of methane, relative to if that emission did not occur.

      GWP* addresses the question as to how much additional net warming will occur from an emission of methane, after taking into account of the fact that historical emissions of methane from that same source will be decomposing.

      Accordingly, GWP100 focuses on the warming caused by an emission, independent of other things that will occur for other independent reasons.
      Conversely, GWP* focuses on the change in temperature that will occur after including the effects of historical emissions.

      As long as groups shout across the gully that ‘I am right and you are wrong’ then there is no possibility of working towards any sort of consensus. The starting point for progress has to be recognition of the perspective that each group is coming from.

      • Paul says:

        ‘Warming caused by an emission’. We don’t have an emission, we have emissions over time.
        You are right that they both use the science. One just uses the science correctly by factoring in emissions over time.
        If the other one was correct, then adding the emission, to another, and another, you would get the right answer. But it doesn’t. As GWP is trying to make a flow emission act as a stock one.
        Try not look at GWP* as being backward or historical. It’s effectively represents warming impacts of GHGs as modelled regardless of whether increasing, stable or reducing’ and does this over time. Forward and back.
        That is what we need. We have future targets through a time period based around limiting warming impact. As a sector we need a plan as to how we will achieve these, and a metric / model that reflects what it achieves.

        But then again as you stated it’s around policy & politics, not the science.

  2. Jason Barrier says:

    Keith, Climate change issues, as you point out, are complex and I agree with most of what you have written above. However, at the risk of being labeled as one of your ‘insulting warriors’, I would suggest the real question here is a very simple one – Who is causing the planet to warm?
    If New Zealand farmers are only contributing to that problem in a minimal way (because of a stable methane cloud) then they should only have to contribute to the costs of any solution in a commensurately minimal way. Any other metric will lead to perverse outcomes (such as carbon leakage – where reductions in low carbon meat from NZ will quickly be replaced with high carbon meat from Europe/US) causing further warming. To use a taxation analogy the current GWP100 emissions-based approach (rather than the GWP* warming-based approach) is akin to the IRD coming along to farmers and saying – we know you are only making a small profit (because your revenues are largely offset by your costs), but we are going to start taxing you on revenue rather than profit because it is more politically expedient for us to do so. Farmers would never accept that, nor should they accept the current approach to taxing methane. Perhaps for your next article, you could examine the logic of why New Zealand sheep and beef farmers receive zero carbon tax credit for the carbon sequestration effect of the 1.4M hectares of native forests on our lands.

    • Keith Woodford says:

      The quick response to your last sentence is that it has to meet the UNFCCC rules of additionality that all countries signed up to. Within that framework, there is scope for looking at the way the additionality rules are applied in NZ. That requires some hard intellectual grunt, and it is difficult for that to occur in amongst the noise that is created by the current shouting.

  3. Horace Smith says:

    It certainly is a contentious issue regarding biogenic methane emission from NZ’s livestock farm systems which we know are amongst the worlds best producing wholesome nutritious safe food. There are inequities within NZ about how best to manage biogenic methane which we must address before we look at the global inequities as we could create a number of unintended consequence.
    The focus must continue to be food production ensuring continued security of supply yet having an acceptable environmental footprint not only for climate but also freshwater and biodiversity plus rural community.
    In NZ we are no longer actively pursuing a strategy of converting bush or draining wet lands (particularly underlain by peat – a deep carbon sink) to farm land. The livestock sectors have plateaued i.e. we have past ‘peak cow’ and there is some reduction. We need to celebrate this because it strongly suggests stabilisation and no further warming – this is momentous. I am deliberately putting aside nitrous oxide emission from this discussion. Now if we examine the NZ livestock sectors we see two major subsectors dairy vs sheep – beef have near equal biogenic methane emission. But there is a strong difference here between these two subsectors having impact upon warming. Yes there has been a swap from one to the other so a degree of cancellation but nevertheless if the focus is warming the recent increase of dairy highlights a warming problem particularly identifiable using GWP*. However the kicker is the recent HWEN Recommendation is applying a heftier emission tax price upon the S&B sector despite this subsector having overall a low environmental footprint (acknowledging some issues about sediment loss and erodible marginal lands) and a warming neutral perhaps cooling methane profile. This HWEN price inequity will have disastrous impact with loss of rural community, the hill country afforested and continued intensive and polluting use of lowlands – not a pretty picture.
    The answer to this conundrum must be balance allowing continued productive farming of hill country with marginal lands within farms afforested (right tree right place) and have land use intensity limited so not adversely impacting freshwater and biodiversity. (the recent expose about Canterbury freshwater and high nitrate levels is a shocking outcome of not doing good due diligence ensuring policy is informed by science and a degree of precaution with polluter pays). So lets get a win – win with a resetting back to New Zealand productivity for food centred upon grass-fed and natural in a integrated manner which is also the key marketing differentiator that should be leveraged.
    To address the global inequity we do have some need to review historic warming but the challenge here is how much. The government has set methane reduction targets 10 percent by 2030; 24-47 percent by 2050. In my reckoning the first is doable but not via cannibalising one sector in favour of another, the second target needs revision and I would pitch up 20 percent as a conversation starter.
    Lets reset to a warming neutral position and then look at further cooling reduction without destroying New Zealand Aotearoa competitive advantage and do what is right.
    The discussion here must incorporate science including GWP* to ensure a focus on warming.

    • Keith Woodford says:

      Yes, but I repeat that the difference between GWP and GWP* does not relate to the science. They are both built on exactly the same science. But they address different question which lead from different value judgements.

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