Why methane should be treated differently compared to long-lived greenhouse gases

New research provides a way out of a longstanding quandary in climate policy: how best to account for the warming effects of greenhouse gases that have different atmospheric lifetimes.

Carbon dioxide is a long-lived greenhouse gas, whereas methane is comparatively short-lived. Long-lived “stock pollutants” remain in the atmosphere for centuries, increasing in concentration as long as their emissions continue and causing more and more warming. Short-lived “flow pollutants” disappear much more rapidly. As long as their emissions remain constant, their concentration and warming effect remain roughly constant as well.

Our research demonstrates a better way to reflect how different greenhouse gases affect global temperatures over time.

Cost of pollution
The difference between stock and flow pollutants is shown in the figure below. Flow pollutant emissions, for example of methane, do not persist. Emissions in period one, and the same emissions in period two, lead to a constant (or roughly constant) amount of the pollutant in the atmosphere (or river, lake, or sea).

With stock pollutants, such as carbon dioxide, concentrations of the pollutant accumulate as emissions continue.

Flow and stock pollutants over time. In the first period, one unit of each pollutant is emitted, leading to one unit of concentration. After each period, the flow pollutant decays, while the stock pollutant remains in the environment (provided by author).

The economic theory of pollution suggests different approaches to greenhouse gases with long or short lifetimes in the atmosphere. The social cost (the cost society ought to pay) of flow pollution is constant over time, because the next unit of pollution is just replacing the last, recently decayed unit. This justifies a constant price on flow pollutants.

In the case of stock pollutants, the social cost increases with constant emissions as concentrations of the pollutant rise, and as damages rise, too. This justifies a rising price on stock pollutants.

A brief history of greenhouse gas “equivalence”
In climate policy, we routinely encounter the idea of “CO₂-equivalence” between different sorts of gases, and many people treat it as accepted and unproblematic. Yet researchers have debated for decades about the adequacy of this approach. To summarise a long train of scientific papers and opinion pieces, there is no perfect or universal way to compare the effects of greenhouse gases with very different lifetimes.

This point was made in the first major climate report produced by the Intergovernmental Panel on Climate Change (IPCC) way back in 1990. Those early discussions were loaded with caveats: global warming potentials (GWP), which underpin the traditional practice of CO₂-equivalence, were introduced as “a simple approach … to illustrate the difficulties inherent in the concept”.

The problem with developing a concept is that people might use it. Worse, they might use it and ignore all the caveats that attended its development. This is, more or less, what happened with GWPs as used to create CO₂-equivalence.

The science caveats were there, and suggestions for alternatives or improvements have continued to appear in the literature. But policymakers needed something (or thought they did), and the international climate negotiations community grasped the first option that became available, although this has not been without challenges from some countries.

Better ways to compare stocks and flows
An explanation of the scientific issues, and how we address them, is contained in this article by Michelle Cain. The approach in our new paper shows that modifying the use of GWP to better account for the differences between short- and long-lived gases can better link emissions to warming.

Under current policies, stock and flow pollutants are treated as being equivalent and therefore interchangeable. This is a mistake, because if people make trade-offs between emissions reductions such that they allow stock pollutants to grow while reducing flow pollutants, they will ultimately leave a warmer world behind in the long term. Instead, we should develop policies that address methane and other flow pollutants in line with their effects.

Then the true impact of an emission on warming can be easily assessed. For countries with high methane emissions, for example from agriculture, this can make a huge difference to how their emissions are judged.

For a lot of countries, this issue is of secondary importance. But for some countries, particularly poor ones, it matters a lot. Countries with a relatively high share of methane in their emissions portfolios tend to be either middle-income countries with large agriculture sectors and high levels of renewables in their electricity mix (such as much of Latin America), or less developed countries where agricultural emissions dominate because their energy sector is small.

This is why we think the new research has some promise. We think we have a better way to conceive of multi-gas climate targets. This chimes with new possibilities in climate policy, because under the Paris Agreement countries are free to innovate in how they approach climate policy.

Improving the environmental integrity of climate policy
This could take several forms. For some countries, it may be that the new approach provides a better way of comparing different gases within a single-basket approach to greenhouse gases, as in an emissions trading scheme or taxation system. For others, it could be used to set separate but coherent emissions targets for long- and short-lived gases within a two-basket approach to climate policy. Either way, the new approach means countries can signal the centrality of carbon dioxide reductions in their policy mix, while limiting the warming effect of shorter-lived gases.

The new way of using global warming potentials demonstrably outperforms the traditional method in a range of emission scenarios, providing a much more accurate indication of how stock and flow pollutants affect global temperatures. This is especially so under climate mitigation scenarios.

Well designed policies would assist sectoral fairness within countries, too. Policies that reflect the different roles of stock and flow pollutants would give farmers and rice growers a more reasonable way to control their emissions and reduce their impact on the environment, while still acknowledging the primacy of carbon dioxide emissions in the climate change problem.

An ideal approach would be a policy that aimed for zero emissions of stock pollutants such as carbon dioxide and low but stable (or gently declining) emissions of flow pollutants such as methane. Achieving both goals would mean that a farm, or potentially a country, can do a better, clearer job of stopping its contribution to warming.

Dave Frame is Professor of Climate Change at Victoria University.

Adrian Henry Macey is Senior Associate, Institute for Governance and Policy Studies; Adjunct Professor, New Zealand Climate Change Research Institute, Victoria University.

Myles Allen is Professor of Geosystem Science and Leader of the ECI Climate Research Programme at Oxford University.

Disclosure statements:

Dave Frame has received relevant funding from Victoria University of Wellington.

Adrian Henry Macey receives funding from Victoria University of Wellington and the New Zealand Centre for Global Studies

Myles Allen has received relevant funding from the UK Department of Energy and Climate Change (now Business, Energy and Industrial Strategy).

This article first appeared on The Conversation. It was not commissioned or paid for by NBR.


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41 Comments & Questions

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I skimmed the last two paragraphs , and read "the primacy of CO2 emissions in the climate change problem".
No need to read further.

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Not if you deny climate change.

This is an article reflecting another article published by the most reputable science journal around that is advocating for measuring the relative impact of the methane belched from cows at a lower rate than we currently do.

It's an article advocating for farmers, Farmer Brown.

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Agree - this research is important for farmers. Provided herd size doesn't increase, then they shouldn't be charged any ETS in relation to Methane. If herd size reduces, then get a credit for methane reduction??

Long term future of dairy in NZ is probably producing the same from less cows, with less damage to the environment.

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Producing the same from less cows at the same payout does not look like the sort of dairy future that anyone would desire.
Producing half the amount, spread evenly across the entire year, at twice the price, would be the best option for restoring the capital that the dairy industry has destroyed in the last 50 years.
That's the various forms of capital , . . . . social and environmental, as well as economic capital.

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Its over Lance you cannot win arguments by perjorative labelling like "climate denier" alone. The movement has lost it's hysteria stage and now the reality of the bad science and appalling economics are coming home to roost on you and your fellow travellers doors,

https://www.wsj.com/articles/climate-change-has-run-its-course-1528152876

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" advocating for farmers"
Pull the other one.
Farmers neither want , nor need such " advocacy".
Farmers are the ones harvesting sunlight , air and water from the atmosphere to make fuel, food, and fibre.
Agricultural products are stores of renewable energy from the sun.

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There are actually people who still believe this climate change conjob? I suppose some people will say anything for research funds - $$$, ka-ching.

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These people are called scientists, and they work for low salaries trying to improve the world. Or ion this case - save it.

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Sort of like priests then?

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That made my lunch Farmer Brown!

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Just like missionaries setting out to convert the ignorant natives to the one true religion. Theirs.
Now Farmer Brown you really must stop your protestations. These people know the one true way. All they are asking of you and other farmers is, "simply close your eyes and think of England".

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They're trying to improve their research funds more like.

The science in the IPCC AR5 Working Group I showed the climate models failing & all the doomsday predictions associated with them. Time is up for the high priests of climatology & their failed doomsday predictions - pointing the bone at the heretics doesn't work anymore.

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Like they saved it from acid rain and the hole in the Ozone layer and other previous doomsday scenarios that never came to pass because were based on faulty evidence and faulty analysis - but people like you got hysterical about!

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Please at least do yourself a favour and read up on CFCs and the role and effects of banning them.

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Yes that one had some credibility (although not uncontested scientifically) for policy basis. Bit sad of course that the universal substitute for CFC's as a propellant is CO2.

Oh well, it's a dirty compromised world

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CFC's are an example of a credible basis for making a policy (although still a scientifically contested one)

Bit sad of course that the universal substitute for CFC's as a propellant is CO2. Oh well, it's such a dirty compromised world..

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There is a New Zealand researcher that had come to the conclusion that CFC's on their own could not have caused the holes in the ozone layer. He conjectured that it was the nuclear bomb testing in the upper atmosphere that acted as a catalyst to the CFC causing a chain reaction leading to the hole in the ozone layer.

Like climate change, many scientists admitted the science on CFC's was unsettled i.e. theories only. One thing that seemed entirely co-incidental; or not, was that the original 50 year patents on the original set of CFC causing refrigeration gases were all set to expire a handful of years before the CFC agenda became known. Since the science was only a theory and unproven, and a major player in the refrigeration gas would have lost a world monopoly and therefore control of the market at the 50 year mark it did cause questions around the science.

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Since when did the level of a person's salary have any bearing on the truth or falseness of what comes out of their mouth?

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What annoys me about the Paris accord is how the goal of these deals (i will include the failed Kyoto) seems to be to enforce a limitation on economies. These agreements always appear not to boost economies in a different direction, but to punish them, one only needs to refer to the Carbon Credit scam.
The largest and easily the most lucrative component of the CDM market, administered under the UN Framework Convention on Climate Change (UNFCCC), is a peculiar racket centred on the manufacture of CFCs (chlorofluorocarbons), classified under Kyoto as greenhouse gases infinitely more potent than CO2. The way the racket works is that Chinese and Indian firms are permitted to carry on producing the refrigerant gas known as HCFC-22 until 2030, but a by product of this process is HCFC23, over 10000 times more powerful as a greenhouse gas than CO2, the firms can then destroy HCFC23 claiming allocations of carbon credits worth billions of dollars in doing so, its a complete con!

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Maybe note should taken of this bit of interesting research. Methane could actually be helpful
http://www.sciencemag.org/news/2017/05/are-methane-seeps-arctic-slowing-...

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We were told in 2007 that the "the science is settled" and shouted out of debates.

CO2 and CH4 are common, naturally occurring molecules and referring to them as "pollutants" is a political choice not a scientific defintion.

What other 'caveats' and shoddy, politicised science from the 1990 IPCC can we expect to be overturned by new research in coming decades as the global warming bandwagon loses steam?

The whole movement was built on the feeblest of facts/observations and a large body of politically-expedient groupthink, media hysteria and outright fraud.

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The principal science is long settled - over 100 years now. This article is one of thousands per year that is working to improve the way we analyse, measure and mitigate climate change.

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And not one of the many thousands of papers has shown that humans can control climate , or as you put it "mitigate climate change".
Laughable really, is it not?

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Remember 2008, when the alarmists predicted the Arctic would be ice-free by 2013?? Since the 70's, not one single prediction by these scientists has come to pass.

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It is not settled now and was not settled then. The only thing settled then was the science related to disturbances in solar radiation caused by solar flares and the further discovery of the eccentric orbit that causes a change in the distance between the earth and sun.

The earth is 150,000,000 km from the sun. The temperature of the surface of the sun is 2,000,000 °C. The earth moves in and out of proximity to the sun by 5,000,000 km. That's a 3.3% variation in distance. Under the inverse square law, the % change in solar radiation (heat) will vary by greater than 3.3%, and that my friend is a lot of heat. The only way the earth does not burn or freeze, is because of thermal mass, and yes, a regulating atmosphere, possible by the regulation of water evaporation from the sea. Just like the human body controls perspiration to regulate body temperature.

If that is not real enough for you, compare it with investing. Stock prices go up and down daily, and calculated potential percentage returns will vary daily, but those with a big reserves (thermal mass) and in the market for the long term will not be phased by daily fluctuations. i.e. short term variations have little short term impact but will produce trends or moving averages. As it is with temperature and climate trends.

It is concerning that you claim to understand the principle when it comes to investing and money, but not the earth we live on. You are asking people to invest based on your understanding of short term and long term variations, yet argue against the existence of the same principle when it comes to complex solar system we live in.

To those that accept the short and long term variations in climate, the concept of man made climate change seems little more than a Nigerian money scam. No-one from the climate change advocates produce specifics that take into account the natural variations of nature and our solar system, and everyone says the science is settled. And no-one talks about the vast quantity of weather modification experiments and advanced weapons testing.

The planet needs greater looking after, and man does dis-respect the planet, but if man has any involvement in change to the planet, it is not industry or cows farting, but the same govt funded institutional sciences that are behind the climate change agenda.

Institutions funded by the same sources that allowed the exploding of 1000 nuclear weapons in our upper atmosphere, cutting holes in the ozone layer with weapons, including testing and deployment of D.E.W. and weather modification weapons. Any proof that exists that man has tampered with climate, is not related to the common man or cows, but to the govt and power elite, who are pushing the climate change agenda.

Govts should not be advocating taxes on the common man, but offering strict control of technology experiments and enforcing resignations and prosecution of those attempting to be climate gods.

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Lance, you may recall from school and university days that getting the right answer (if you got the right answer) may only earn you 25% of the credits. In many cases what school and university wanted was to know that you understood the question and the formulae and method to arriving at the correct answer. Providing the 'working out, formulae and calculations' was worth more than the answer itself. This would also involve handling the effects of variables and offsets that would impact the final equation. You could get the answer right, but without showing reference to all contributing factors it was considered a fail.

Stating "the science is settled" the when proponents never make any reference to or variance offset of the significant impacting variables indicates they have never considered or investigated those significant variables. Or they have ignored those significant variables. In these instances, we do not call it science. We call it by its rightful name - propaganda.

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I never went to Uni. but my folk taught me that truism that I've never forgotten. And that is, "if in Maths, Science or reasoning, should you start with incorrect inputs then your conclusion MUST ALWAYS be incorrect.
The climate is changing. YES
Now could someone answer me this please.
If the "Paris agreement" enthusiasts, Al Gore et al got everything they wanted. How many years would that add to the existence of man on earth? And, what temperature would man enjoy during those hard won final years?

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Don't kid yourself John, none of the man made climate change numpties could ever answer that question.

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Commonly called GIGO. Garbage in, Garbage out.

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The science is only settled in relation to CO2. The problem is trying to account for other gasses as if they are also CO2. And that is where the stuff up has occoured.

For example, the UN has stated that NOx emissions from shipping break down atmospheric methane. And as a result, long distance shipping has an overall reduction in global warming.

Yet Volkswagen were fined for emitting more NOx, and the side effect of that was their cars used less fuel than otherwise. So in effect Volkswagen were fined for helping the environment. The reason they were punished - Because an easy 20% saving of fuel usage is possible by cheating the NOx emissions. That also means a 20% reduction in petrol and diesel taxes paid to European governments. As well as 20% lower petrol and diesel sales. And oil companies are often partly government owned.

So Volkswagen are actually getting punished solely because governments are not happy about loosing billions in tax revenue from lower petrol and diesel sales.

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“George Orwell said that some ideas are so foolish that only an intellectual could believe them, for no ordinary man could be such a fool.", the Climate Change con is ably abetted by the greed of western governments trying to milk this tax cow for all its worth but thank god people are waking up to this nonsense

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A possible solution is to have cows weaned off grass and gradually introduced to astro turf. They would leave a zero carbon hoof print.

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Yes! But only if the gradual rate was in line with the historical rate of beneficially accumulating randomly occurring mutations. So yes, a possible solution..:)

A more immediate solution would be to simply recognize that animals are carbon recyclers not net emitters and are therefore not a problem.

Mechanized farming systems of course emit hydrocarbon forms of additional carbon but without these mechanical beasts the human population would have starved generations ago and rather than our forebears having once been serfs and peasants this would still be the good life for the majority of us

The more that fallacious assumptions persist in being unchallenged the more the dilemmas, and vexed handwringings multiply

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What, replace the real cows with plastic blowup ones? What will you do with the plastic when they "die"?

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Quite sad the way lobbyists and industry voices have turned so many on the right into people who will ignore science in a quasi-religious way, simply for the benefit of those who will profit from doing so.

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You must be automatically dissing threads, blogs, websites and news articles that challenge the concept of man made global warming, and have never read any. Most challenge the lack of logic of the man made climate change advocates, including the fact that the advocates themselves appear to operate in a quasi religious way:
-Stating the the science is settled.
-Quoting from something someone has written that is quoted from something someone has written without answering specific questions or willing to debate the principles.
-Other inputs to potential climate change get ignored.

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My concern with the research is twofold: 1) Whilst Methane is in the atmosphere it acts as a warming agent something like 89 times more efficiently than CO2 so for 12 years or more it has a very strong warming effect. This is not adequately reflected in CO2 equivalent measures because the effect is averaged over 100 years. 2) When Methane decays it becomes CO2 with a half life of some 50 years and an even longer total warming effect. I cannot see this effect reflected in this new research.

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I hope the planet's wetlands, peat bogs and Amazon rain forests stop their methane burping.

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Arguments for methane production affecting CO2 production completely ignores that fact that farting animals have been around for millions of years, and in greater quantities than today. I'm sure T-Rex let off a few good ones.

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CO2 does not have a half life of anything if it gets gobbled up by a plant, a tree, moss, or absorbed into the vast CO2 sink called the ocean to be converted back to oxygen by plankton.

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