Burps & Bluster
Are farmers doing enough on methane? Methane from Kiwi farms accounts for more than a third of the country’s greenhouse emissions. But exactly how this gas contributes to global warming and to what extent it should reduce is complex. As our methane targets look set to be overhauled, George Driver investigates how the gas heats the planet and how low our emissions should go.
By George Driver
There’s surely no other nation on Earth as preoccupied by cow and sheep burps as New Zealand.
But for good reason. Think of a typical New Zealand farm and you’ll probably picture a Country Calendar scene of rolling green pasture with a snowy peak in the background, or the golden tussock of a high-country station. No clouds of smog; no smoke stack chimneys. But our cows and sheep produce more climate-warming gas each year than our entire transport and electricity sectors combined.
If you look at a pie chart of New Zealand’s greenhouse emissions, agriculture takes up about half the dish. Methane from agriculture — a gas that’s produced by ruminants as they digest grass — takes up more than a third of the pie. No other country in the OECD has such a high proportion of methane in their emissions mix — the average contribution from agriculture is just 10 per cent.
So, while many countries are focused on closing coal power stations to reduce greenhouse emissions, New Zealand — already boasting one of the world’s most renewable electricity networks — has been debating how to regulate cow burps for over two decades.
Just how much our methane emissions should reduce is probably one of the most important questions in New Zealand’s climate change policy. But there’s more to this greenhouse gas pie than meets the eye. While methane accounts for a third of our emissions using one metric, it doesn’t necessarily account for a third of the warming our emissions cause. And while climate scientists are unanimous that CO2 emissions must go to net-zero to limit global warming, exactly how much methane emissions should reduce is less clear-cut.
So what are the real differences between CO2 and methane, how do we account for this, and how low should our methane emissions go?
Two different gases
As Dave Frame attempts to explain the intricacies of how methane warms the planet, he seems exasperated. Frame is one of the country’s leading climate scientists. He’s been an author for the Intergovernmental Panel on Climate Change (IPCC), a director of Victoria University’s Climate Change Research Institute, and is now a physics professor at the University of Canterbury.
For more than a decade, he’s been trying to explain to New Zealanders that most of us are looking at our methane emissions all wrong. But trying to get New Zealand politicians, public servants, journalists and the public at large to understand the gas seems to be a never ending task.
“I feel like we’ve been through this so many times,” he says. “The logic keeps being the same and every time we have the conversation people go ‘yeah, I suppose that’s right,’ but boy is it painful.” To be fair to the public, trying to understand it can be painful too.
For Frame and many other climate scientists, methane isn’t exactly the global warming bogeyman that many believe — at least not when compared to carbon emissions. While it is an incredibly potent greenhouse gas, its short lifespan means its impact on the climate is vastly different to CO2.
Methane isn’t exactly the global warming bogeyman that many believe — at least not when compared to carbon emissions. While it is an incredibly potent greenhouse gas, its short lifespan means its impact on the climate is vastly different to CO2.
Essentially, CO2 emissions last for a millennia or more and this means that ongoing CO2 emissions keep accumulating in the atmosphere indefinitely, heating the world more and more. Methane, however, lasts in the atmosphere for about a decade on average and is almost entirely gone from the atmosphere within about 50 years, although a small amount of warming persists for more than a century.
This short lifespan means methane emissions don’t accumulate indefinitely like CO2. On the other hand, methane is extremely powerful while it persists in the atmosphere, with a warming effect about 80 times greater than CO2 over its first 20 years.
To use an analogy, CO2 emissions are a bit like filling up the bath with the tap on low and the plug in. Every drop of water keeps slowly increasing the bath level (and the temperature). You can turn the tap up and down (or increase or reduce emissions) but every drop is still raising the level of the bath.
The effect of methane emissions is more like turning the tap on high with the plug out. The water level rises fast, but then stabilises as the amount going down the plughole matches the water from the tap (as methane breaks down). Turning up the tap (or increasing emissions) can still raise the bath level, but turning down the tap (or reducing emissions) results in the water level (the temperature) subsiding.
So while methane still warms the planet, ongoing emissions don’t accumulate and increase the temperature indefinitely like they do with CO2. The rate of decay means that methane emissions need to fall by about 0.3 per cent a year to no longer cause additional warming — for the water coming from the tap (ongoing emissions) to match what’s going down the plug. The emissions have still made the planet warmer (and the bath level higher), but they’re not increasing the temperature any further. This has the same temperature effect as CO2 emissions falling to net-zero, as the warming from past CO2 emissions is essentially locked in because it takes so long to break down.
If methane emissions fall faster than 0.3 per cent, however, then it will actually reduce the warming caused by the gas, like a cooling effect — with the same effect on the climate as planting trees to sequester carbon.
Also, if you stop emitting methane, then the warming caused by the gas soon drops and eventually disappears entirely. However, stopping CO2 emissions doesn’t stop the ongoing warming caused by earlier emissions, which are locked in for centuries.
Frame says this is why CO2 emissions must go to net-zero to halt global warming, whereas methane emissions can stop additional warming with a very gradual decline. He likens methane’s effect to the health impact of obesity and carbon emissions to terminal cancer. “You would want to address both,” he says. “But the really time-critical one is the cancer.”
This distinction, Frame believes, has been lost in public debate on methane emissions and, significantly, in how our greenhouse emissions are reported.
Other climate scientists, however, view methane as a more menacing presence. Andy Reisinger is probably Dave Frame’s main methane adversary. His bovine-burp credentials are also among the best in the country. He was deputy director of the New Zealand Agriculture Greenhouse Research Centre (NZAGRC) for a decade and has been an author on multiple IPCC reports. He is currently a climate change commissioner, advising the government on meeting its emissions targets.
Reisinger believes that just because stable methane emissions don’t cause the same increase in warming as CO2 that doesn’t mean that we shouldn’t do all we can to reduce the emissions as much as possible. Every tonne of methane is making the planet warmer than it otherwise would be and reducing it can avoid that additional warming. While there’s little we can do about the warming locked-in by past carbon emissions, actively putting methane into the atmosphere is within our control.
“Even if falling methane emissions don’t cause additional warming, that says nothing about if it’s something we ought to reduce,” Reisinger says. “To use a crude analogy, if a farmer has always dumped 10 bags of fertiliser into a river each year, the river will not get any more polluted. That doesn’t mean that I should continue to dump 10 bags of fertiliser into a river. There’s nothing positive about it.”
A complicating factor is that the way we calculate greenhouse emissions doesn’t factor in how these two gases accumulate differently.
When the first global efforts to reduce greenhouse gases were beginning, a metric was developed so all of a country’s greenhouse emissions could be reported and compared using a single figure.
Because greenhouse gases all warm the atmosphere at different rates and break down over different time frames, you can’t simply add up all the gases to show how much each country is warming the atmosphere. So in the early 1990s a formula was developed, dubbed global warming potential 100 (GWP100), which has been the fundamental metric for expressing every country’s greenhouse emissions and targets ever since.
GWP100 is calculated by averaging the warming produced by each greenhouse gas over a century, and equating this with the warming from emitting a tonne of CO2. The figure is then reported as CO2- equivalent (CO2-e), or often just using the catch-all term “greenhouse gas”. Using GWP100, methane emissions are multiplied by 27 (the exact multiplier varies as science develops), so a tonne of methane equates to 27 tonnes of CO2-e, or 27 tonnes of greenhouse gas.
It’s a useful metric because it is simple to calculate and makes it easy to compare countries’ emissions. But it has some limitations.
GWP100 shows the warming caused by emissions as if they are one-off occurrences, comparing how those emissions will warm the planet compared to zero emissions. But if you try to add up these emissions over time, or calculate how emissions have increased or decreased over time, the figures don’t actually tell you how much warming these emissions have caused. This is because GWP100 essentially treats methane as if it accumulates indefinitely, like CO2, and so doesn’t account for the fact declining methane emissions can stabilise or reduce warming, while CO2 emissions always increase it.
This obscures how a country’s ongoing emissions will warm the atmosphere. For example, if a country is emitting a million tonnes of methane a year and no CO2, but the emissions were declining at 0.3 percent a year, then it wouldn’t be causing additional warming — the planet would be warmer than it would be without those emissions, but it wouldn’t warm further — the same effect as net-zero CO2. However, using GWP100, the country’s emissions would look the same as if it was emitting 27 million tonnes of CO2, which would be significantly adding to global temperature.
On the other hand, GWP100 underestimates the warming from rising methane emissions, which have a significant warming effect due to how powerful it is in the short-term.
With every country emitting different ratios of CO2 and methane, it becomes impossible to accurately show what a country’s emissions will do to the climate solely using GWP100.
“It’s like having a metric that combines the health impact of litres of alcohol per day with kilograms of arsenic,” Frame says. “It’s just a bad mix in terms of units.”
While it sounds controversial, the IPCC made the shortcomings of GWP100 clear in its latest report: “Expressing methane emissions as CO2 equivalent emissions using GWP100 overstates the effect of constant methane emissions on global surface temperature by a factor of 3 –4 while understating the effect of any new methane emission source by a factor of 4–5 over the 20 years following the introduction of the new source.”
For most developed countries this isn’t a significant issue as their methane emissions are a small proportion of their greenhouse profile. But for New Zealand, Frame says it’s significant.
“GWP100 is clear, simple and misleading,” Frame says. “And the clarity and simplicity is attractive to some people. But for countries like us, it’s a big deal. And although high methane emissions are unusual for a developed country, most developing countries have profiles like ours. But we’re left with this relic from a bygone age.”
A rising star?
Other metrics have been developed which can accurately show the warming eff ect of ongoing emissions — but whether that’s a good idea or not, and whether the shortcomings of GWP100 matter, is fiercely debated.
About a decade ago, Frame worked with climate researchers from Oxford University to develop a new metric called GWP*. The project was led by Oxford professor Myles Allen, someone Frame calls “one of the leading climate researchers of his generation”.
Allen became one of the first scientists to highlight that global CO2 emissions must reach net-zero to halt global warming — work that Frame was intimately involved with while working at Oxford as a researcher.
“It was really Myles’ insight that temperatures change depending on the cumulative emissions of CO2,” Frame says. “He showed that you have to get to net-zero carbon emissions to stop warming. This was a significant reframing of climate policy, because up until then people had been talking about stabilisation and equilibration of temperatures. They thought if we reduced CO2 emissions by 75 per cent that it would be possible to stop warming by 2100. We showed this wasn’t really the case. But it was a bit of a fight.”
The BBC later dubbed Allen “the physicist behind net zero”, and the concept has become the foundation of countries’ eff orts to limit temperatures to below 2°C — and as close to 1.5°C as possible — under the historic Paris Agreement of 2015.
Allen, Frame and others later developed the GWP* metric to accurately show how changes in global emissions would affect temperatures. Unlike GWP100, the GWP* metric accounts for the rate of methane emissions to show how they will affect temperatures.
Using this metric, if a country’s methane emissions were falling at 0.3 per cent a year, then the gas’ contribution to further global warming would be zero, accurately reflecting how its emissions would affect temperatures.
On the other hand, if methane emissions were rising, then the warming effect is amplified. “It finally enabled us to treat short-lived gases in the same way that you treat CO2 in a carbon budget,” Frame says.
In effect, this would mean that if New Zealand’s methane emissions fell by 10 percent each decade, then using the GWP* metric, a third of our greenhouse emissions would effectively be wiped from our greenhouse account balance sheet.
Frame says given the Paris Agreement commits countries to achieving a temperature goal, it is essential to use a metric that shows how countries’ emissions affect temperatures.
However, efforts to replace GWP100 have failed to gain traction. Partly, Frame says this is because GWP100 has been used for emissions targets and reporting for 30 years.
“There’s been criticism of GWP100 for decades, ever since it was created really, but because it plays a role like a joint in a body — it’s a hinge between science and policy — it’s quite hard to replace. People get very uptight about it and it gets its own inertia. But we’re clearly right about the physics and no one disputes that.”
Frame believes pressure to change the metric, or to account for methane emissions separately, will gather momentum, however. “Other countries will encounter this problem — places like Uruguay, Argentina and Thailand, where methane from rice or ruminants is quite a big factor. And if and when those countries get around to thinking about climate policy, they will face the same sort of issues that we face, and you’re likely to hear them go ‘hang on, this is not quite the right way to do it’. So it’s not true that we are unique, it’s just that we’re the first cab off the rank in terms of being expected to mitigate. The current state is unsustainable in the long run if we’re serious about limiting temperatures.”
He’s found it baffling that New Zealand diplomats haven’t advocated for a metric change, or for methane targets to be reported separately in global agreements. “It strikes me as odd that it’s not a positive thing that if we cut methane we reduce our contribution to warming.”
Frame’s not alone in this advocacy. Notably he’s collaborated on a number of articles with Adrian Macey, who served as New Zealand’s first climate change ambassador from 2006 to 2010 and became chair of the UN climate change negotiations under the Kyoto Protocol. Myles Allen and other climate scientists at Oxford have also been highlighting these issues.
Unsurprisingly, major agriculture groups have supported a change too. Focusing on warming, rather than emissions, could transform how the sector’s contribution to climate change is accounted for. Beef + Lamb New Zealand, DairyNZ and Federated Farmers recently commissioned a report by Allen and his Oxford colleagues on how New Zealand’s emissions targets would contribute to warming.
Allen has even suggested that farmers could be rewarded for the cooling effect caused by falling emissions as this would have the same effect on the climate as planting trees.
“That’s a sensible conversation to have,” Frame says. “We reward foresters for their contribution to lowering global temperatures, so why not reward farmers for lowering theirs.
“The opposition to that is that farmers are still heating the world, but you could say the same about a fossil fuel company that has reached net-zero. Their past emissions are still keeping the world hotter and they aren’t forced to undo that warming, but there’s nothing preventing them from off setting that warming by planting forest.”
Others have a vastly different view.
Efforts or outcomes?
Andy Reisinger — along with many of his colleagues — looks at the issue of New Zealand’s methane emissions very differently to Frame. He says, while GWP* can more accurately show how emissions will change temperatures, this doesn’t necessarily make it the best metric to guide action on climate change.
Reisinger is not convinced that not causing further warming is an adequate goal for a developed country, especially for a country with a high share of short-lived emissions. The goal is to do all we can to contribute to global efforts to combat the climate crisis and reducing methane emissions as much as possible will help slow the rise in temperatures.
“Is fairness causing the same amount of climate change, or does fairness mean putting in the same effort? I think most people would think, on reflection, that fairness means putting in the same effort, rather than having the same outcome.”
Reisinger points out that New Zealand’s Climate Change Response Act’s aim is to “contribute to the global effort” to limit temperatures to 1.5 degrees above pre-industrial levels — not to halt our own contribution to warming.
“There’s full agreement on the physics of GWP*, but that doesn’t mean it’s a meaningful measurement of what’s adequate,” Reisinger says. “There’s no good reason, in my view, why not causing additional warming from methane is an
adequate contribution towards a global problem.”
To what extent farmers should be expected to reduce the warming they cause, however, is a value judgement that’s difficult to determine. “There’s nothing in science that tells us how much our contribution to a global problem should be,” Reisinger says. “The question is only how low can we go without breaking our rural communities, without breaking our economy, without breaking our collective willingness to actually do something about climate change.”
Reisinger believes GWP* also masks New Zealand’s contribution to global warming. The anthropogenic warming caused by New Zealand since 1850 has overwhelmingly come from methane, but applying GWP* to recent emissions ignores this, treating major methane emitters and methane minnows basically the same.
“With GWP100, having zero emissions means you’re not emitting any greenhouse gas, whereas with GWP* zero means I’m emitting an unspecified amount of methane in perpetuity that’s reducing slowly over time,” Reisinger says. “You could be emitting a million tonnes of methane, or one tonne, but as long as emissions drop by 0.3 per cent a year, then using GWP* my emissions will be reported as zero. Yet, if I’m emitting a million tonnes of methane, my ability to reduce those emissions is greater than if I’m barely emitting any methane at all. And a million tonnes of methane is making the world significantly warmer compared to one tonne.”
The advantage of GWP100 is that it compares the warming effect of emitting a gas compared to not emitting that gas, which is useful for directing action on climate change, Reisinger says.
There’s an added advantage in cutting methane emissions, too. Because it breaks down so quickly, this has a more rapid effect on temperatures. Others have argued that reducing methane as a priority can “buy time” to reduce CO2 emissions. Although Reisinger doesn’t believe we should prioritise methane, but reduce it in addition to net CO2 emissions.
“The 21st century, which some of us care about, would be cooler if we nominally achieve the same emissions targets but prioritise methane over CO2, and that’s not a trivial thing. I don’t know of any government policy that focuses on the 22nd century.”
However, Frame says that even stopping all methane emissions would only reduce temperatures by a few tenths of a degree, and CO2 increases would wipe out any gains within a decade or two. “I’d like to see us reduce our methane emissions, but I see that as less central compared to CO2. Getting to zero on CO2 is going to be a mammoth job and we’re totally not on target for that. This is where I find the methane conversation a weird distraction. Once we reach net zero and halt methane’s contribution to warming, then you can decide whether you want to plant more trees or shoot more cows to reduce your warming levels further.”
Two sides of the argument: Climate scientist and physics professor Dave Frame (left) believes we’re wrong about how we calculate the warming effects of methane; Andy Reisinger (right), a climate change commissioner, says even if methane is not as long-lasting, we should still do all we can to reduce it. Photos: NZ Herald/Mark Mitchell and IISD/ENB
A moving target
While the debate sounds abstract, it’s one New Zealand will likely be having in the coming months. The National Party has committed to reviewing New Zealand’s methane targets if elected.
New Zealand’s emissions targets were set in 2019, when the Zero Carbon Bill was passed, putting a net-zero 2050 target into law. Significantly, the law set different targets for CO2 and methane, recognising their different effects on the climate, although this put us out of step with most of our peers, who have net-zero targets for all greenhouse gases.
During consultation on the Act, Federated Farmers and Beef + Lamb supported the net-zero carbon target, but called for the methane target to be lowered to be consistent with causing no further warming.
However, an overwhelming majority (91 percent) of submissions wanted all greenhouse gas emissions, including methane, to reach net-zero by 2050. Three-quarters of the submissions were templates from Greenpeace and Generation Zero, but still 58 percent of unique submissions supported a net-zero all-gas goal.
In the end, the act legislated a methane reduction of between 24 and 47 percent by 2050, with an interim goal of a 10 percent cut by 2030. All other gases must reach net-zero.
While the target for long-lived gases will result in no further warming from New Zealand by 2050, meeting the methane target could result in a “cooling” effect — at least compared to current elevated temperatures — because it would partly “undo” the warming caused by methane to date. This could mean we halt our contribution to further global warming ahead of other countries meeting an all-gas net-zero target. A report produced by Reisinger for the Parliamentary Commissioner for the Environment (PCE) in 2018 found that methane emissions would have to reduce by 10 to 22 percent by 2050 to cause no further warming.
The PCE later clarified that it wasn’t advising the government to adopt this as a methane target. In fact it recommended going beyond a target that resulted in no further warming from methane.
A recent report by Myles Allen, funded by Beef + Lamb New Zealand, DairyNZ and Federated Farmers, found that meeting the 47 per cent target would essentially mean the warming caused by New Zealand’s emissions would return to 2022 levels after peaking in the 2030s. This was because the “cooling” effect of falling methane would basically undo the additional heating from CO2.
The methane target in the act was taken from a 2018 IPCC report, which looked at what emissions reductions would be required to limit global warming to 1.5°C. It ran five different scenarios for how this could be achieved, detailing different emissions reductions in different sectors. Methane emissions from agriculture reduced by between 24 and 47 percent in three out of five of the pathways. It’s this “interquartile range” that became our national target. The other two IPCC scenarios involved methane emissions increasing by 2 percent, and decreasing by 69 percent.
The IPCC report was explicit that these were global scenarios that shouldn’t be used to set national emissions targets. In an article published on Newsroom, Myles Allen, a lead author of the report, said “don’t justify targets simply by following ‘what happens in the IPCC’s 1.5°C
scenarios’”. “The scenarios provide background information, but I would not rely on them as a basis for national policy.”
While the bill passed with unanimous support (Act opposed it but missed the vote), National said it would repeal the methane target if elected. Instead, it wanted the target to be set by the independent Climate Change Commission, which was created by the bill. National’s policy is now to “review methane targets for consistency with no additional warming from agriculture”. Allen’s analysis estimates this would require reducing methane emissions by between 15 and 27 per cent — although his report also said that wasn’t necessarily a fair target.
The Climate Change Commission is also required to review the targets next year. However, it can only recommend a change to the target if there has been significant change in circumstances since the targets were set.
Frame believes a zero-warming goal is a good starting point. “Warming should be the foundation of our policy — stop the warming and look to decrease it if we can. I think most New Zealanders would probably think that that was a reasonable starting position.”
For Reisinger, our methane target is a question of values, not science. “How much effort do we think is appropriate for New Zealand to make? Physics can’t tell us the answer. Physics can only tell us what amount of emissions can lead to no additional warming from a particular gas, but that’s not the answer to what is our appropriate contribution to a global social, environmental and economic problem.”
The debate about our cow and sheep burps looks set to continue for some time yet.
This story appeared in the November 2023 issue of North & South.