Methane belched out by ruminant animals is responsible for 71% of our total agricultural emissions. Reducing methane is essential if New Zealand is to meet its national and international targets.
So how exactly is methane produced, and how does it contribute to climate change? There are a lot of different stories out there, but this is how it actually works.
Methane comes from several places, including wetlands, landfills, forest fires, agriculture and fossil fuel extraction. But here in New Zealand, the largest proportion by far is belched out by livestock.
[What, all livestock?]
[Not us, surely!]
It’s perfectly natural. Microbes in the fore-stomach of ruminant animals, like cows and sheep, break down the pasture the animals have eaten and produce methane. And, well, it has to come out somehow.
Great … but it breaks down though, right?
Well, it’s true that methane released into the atmosphere breaks down much faster than other greenhouse gases like carbon dioxide. But while it exists, it has a big impact. Tonne for tonne, methane is actually many times more effective at absorbing heat than carbon dioxide.
An emission of methane will mostly disappear from the atmosphere within 50 years. But while it’s up there, every molecule traps lots of heat. An equivalent emission of carbon dioxide traps less heat, but stays around much, much longer. Thousands of years in fact.
We’ll show you what it looks like. Let’s say filling up the board with symbols is equivalent to a certain temperature increase.
I’m emitting carbon dioxide into the atmosphere every year. Because CO2 takes so long to break down, every emission adds to the warming caused by previous emissions. The amount of CO2 increases over time, and the effects become bigger and bigger.
Okay. I’m emitting methane into the atmosphere. Each emission makes a big contribution to warming, but fortunately we’re not emitting nearly as much methane as we are carbon dioxide.
So as we do this, Gavin is going to rub out the methane symbols to show they break down at a much faster rate in the atmosphere, and I’m going to continue emitting at the same rate.
So if we keep emitting the same amount of methane, the amount in the atmosphere levels out, because the new emissions by and large just replace the previous emissions that have now disappeared.
[So, what’s the problem?]
[New burps replace the warming caused by old ones.]
But, we’ve increased our methane emissions a lot over the past century. This has pushed temperatures up already, and globally they’re still going up.
If we keep emitting methane at the current rate, that will keep the atmosphere a lot warmer than it used to be.
So, at a minimum, if we want to stop additional warming from methane we need to reduce the amount of emissions.
They don’t have to be stopped completely, but the more that they’re reduced, the less warming is caused and the better for the climate. How far could we go?
[I don’t mind a change of diet!]
Climate change is a complex challenge. But we’ve already achieved heaps thanks to some clever Kiwi innovation and farmers becoming more and more efficient. But there is more that we can do. New technology will play its part, but there’s more that you can do now. Find out what in our next video.
Produced by the New Zealand Agricultural Greenhouse Gas Research Centre. Funded by the New Zealand Government
Where does methane come from?
Methane has several sources, including wetlands, landfills, forest fires, agriculture and fossil fuel extraction. In New Zealand, the largest proportion by far is belched out by livestock.
Ruminants such as cows, sheep, deer and goats have four-chambered stomachs, enabling them to readily break down and extract energy and nutrients from fibrous plants like grass. Microbes in the rumen break down complex carbohydrates into simpler molecules—a process known as enteric fermentation. Some of these microbes produce methane, which the animal then mostly burps out.
What influences how much methane an animal produces?
The amount of methane produced by an individual ruminant animal is directly linked to how much it eats, as shown in the graph below:
New Zealand studies indicate that approximately 21-22 grams of methane are produced per kilogram of dry matter eaten. This varies only slightly across the typical feeds in New Zealand’s pastoral systems: fresh pasture (rye grass and clover), pasture silage and maize silage.
The average dairy animal produces approximately 82kg of methane per year, the average deer approximately 22kg per year, and the average sheep approximately 12kg per year.
As highlighted at the top of this page, there are several actions that can be taken now to help reduce methane emissions at the farm level. You can click or tap on those actions to read more.
There is also considerable research underway looking at new approaches. You can read more on the Future actions page.
This video also gives a helpful overview.
Farmers have been asking: what can I do to reduce emissions on my farm? Well, there are three gases we need to reduce: carbon dioxide, nitrous oxide, and methane. But on-farm, it’s particularly about the last two. Lots of small steps can add up to make a big difference.
The good news is that combined greenhouse gas emissions from New Zealand agriculture are no longer going up, thanks to farmers’ efforts to become more and more productive and efficient over the years. As a result, the greenhouse gases emitted per unit of product are going down.
Without all this great work, emissions from agriculture in New Zealand would be about 30 percent higher than now, to produce the same amount of food.
[But there’s a lot more of us now.]
[And a lot fewer of us!]
But we need to reduce emissions, not just keep them steady. There’s no magical formula here, but there are several things that can be done on farms right now – and some will have other benefits too.
You know your business better than anyone, so you’re in the best place to work out which of these are achievable.
Here’s what some farmers are doing already, that you might want to consider for your farm.
First, find out what your farm’s greenhouse gas emissions are and include them in your planning. Depending on the farm, it might be that some of those options can save you time, and money.
In a nutshell, methane emissions are related to the total amount of dry matter eaten. Nitrous oxide emissions depend on the total amount of nitrogen going through your farm via feed and fertiliser. So, what steps can be taken to change these quantities, while still running a profitable business?
Look carefully at the feeds used. Can you use feeds with lower nitrogen or higher energy content to get animals to market quicker? Would a less-intensive system work for you? It might be reducing fertiliser inputs and stocking rates, changing the ratio of your stock type, or once-a-day milking.
You could try using precision technologies for improving the amount and timing of your fertiliser application.
Look at the balance between individual animal performance and stocking rate. Could you run slightly fewer animals and focus more on getting the most out of each animal to keep production up?
You could also consider the balance of your land use to reduce livestock emissions. Many farmers are now integrating trees onto their less productive land, and there is Government support to help do this.
For some farms, diversifying some of the land use to cropping or horticulture could reduce overall emissions and dependence on one income stream.
Rest assured, you’re not alone in your efforts. Scientists are working hard on new solutions, with some very promising results. Some of them are being trialled already. In the future, it’s likely we’ll be able to breed low-methane animals or use inhibitors and vaccinations to reduce the amount of methane that animals belch out.
We’re all working towards the same goal, and any small step is a step in the right direction.
Remember to check out our website for lots more information. Thanks for watching.
Produced by the New Zealand Agricultural Greenhouse Gas Research Centre. Funded by the New Zealand Government
Is methane really an issue?
In short, yes. Scientists estimate that methane emissions are responsible for almost 40% of the total warming effect generated by human activities so far.
Carbon dioxide and nitrous oxide are long-lived gases. Nitrous oxide stays in the atmosphere for centuries, and carbon dioxide for millennia. Therefore, every unit emitted today increases their concentration in the atmosphere and adds to the warming caused by past emissions. By comparison, methane is a relatively short-lived gas—virtually all of the methane emitted today disappears within about 50 years. So new methane emissions today replace, rather than add to, previous methane emissions.
However, while methane is up there, it's much more effective at trapping heat than carbon dioxide. Averaged over 100 years, one tonne of methane causes about 30 times the warming as one tonne of carbon dioxide. Some of the heat trapped by methane causes other changes in the global climate system as well, resulting in warming that extends beyond methane's relatively short lifetime in the atmosphere.
Because methane doesn’t accumulate in the atmosphere in the same way that carbon dioxide and nitrous oxide do, methane emissions don’t need to reduce to zero to stabilise the climate. But ongoing methane emissions keep Earth a lot warmer than it would be otherwise. Reductions will help slow climate change and are critical for keeping warming to well below 2°C (ideally 1.5°C) above pre-industrial levels. Reductions are also needed to meet New Zealand’s own greenhouse gas emissions targets, which for methane are:
- By 2030, methane must reduce to 10% below 2017 levels
- By 2050, methane must reduce to 24-47% below 2017 levels
For more on the targets, see the Government and climate change topic page.
Isn’t methane carbon neutral?
Many people ask whether methane is part of a 'carbon neutral cycle'; carbon in and carbon out meaning that it doesn't need to be reduced. Unfortunately, it's not as simple as that.
All carbon dioxide absorbed into grass and eaten by grazing animals eventually returns as carbon dioxide to the atmosphere and is therefore part of a closed carbon cycle. However, it is the conversion of some of the ingested carbon into methane that causes the challenge.
Methane contains the same amount of carbon as carbon dioxide but behaves very differently in the atmosphere—as described in the section above. So, while the cycle remains carbon neutral, it is not greenhouse gas or warming neutral.
See the NZAGRC website for more on how livestock affect the carbon cycle.
Other helpful resources
For more on methane:
- Watch this presentation on why methane matters by Dr Harry Clark, Director of the New Zealand Agricultural Greenhouse Gas Research Centre and member of the Climate Change Commission
- Read this technical report on New Zealand's methane emissions from livestock, commissioned by the Parliamentary Commissioner for the Environment (PCE), and another PCE report on Understanding the biological greenhouse gases
- Check out how methane from livestock contributes to climate change in this diagram [PDF, 169 KB] by the Ministry for the Environment.
- Read information on methane from the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC)
- Farmers Weekly article 29.07.19: The methane problem [PDF, 115 KB]
- Information on methane from the Australian Academy of Science