Greenhouse gas experts provide an understanding of the methane debate

Parliament will decide on the pathway for tackling our greenhouse gases (GHGs) after the current consultation on the proposed Zero Carbon Bill, the New Zealand Agricultural Greenhouse Gas Research Centre observes in a post on its website.

The Bill presents three broad scenarios –

* net zero carbon dioxide by 2050, which would reduce net carbon dioxide emissions in New Zealand to zero by 2050 (but would not set a target for other gases like methane or nitrous oxide);

* net zero long-lived gases (mainly carbon dioxide and nitrous oxide) and stabilisation of emissions of short-lived gases (mainly methane) by 2050; and

* net zero emissions by 2050, which would reduce net emissions across all GHGs to zero by 2050.

These aren’t “either/or” alternatives, the research centre says. The choice can sit anywhere along the spectrum spanned by those targets.

The term “stabilisation” does not necessarily mean doing nothing. It could also mean reducing methane emissions to a stable level lower than today.

As the co-ordination centre for research aimed at developing technologies and practices to reduce the full suite of GHGs generated by agriculture, the NZAGRC is offering information on the science of GHGs to help inform the debate.

Here’s what it says…

Methane – The Facts

Methane is a very powerful greenhouse gas. It very clearly contributes to global warming. In fact, the Intergovernmental Panel on Climate Change estimates that global methane emissions are responsible for more than 40 per cent of the total warming effect so far of all human activities.

It is short-lived compared to carbon dioxide, which stays in the atmosphere for centuries to millennia, but “short-lived” still means it stays around for decades. Plus, our output of methane has increased markedly over the last 100 years. There’s a lot more methane in the atmosphere now than there was for hundreds of thousands of years.

That increased methane concentration keeps the Earth warmer than it was and — together with warming caused by other GHGs — will make it warmer than we want it to be. Along with carbon dioxide and nitrous oxide, methane is a major contributor to climate change.

The more of these gases we have in the atmosphere, the warmer the Earth will get. The less we have, the less warming we get.

New Zealand has made a commitment under the Paris Agreement to limit warming to well below 2 degrees C, and even aim to keep the rise as low as 1.5 degrees C. To achieve this, we have to stop the amounts of greenhouse gases in the atmosphere from increasing further, but also reduce their amounts where possible.

When it comes to the task of minimising the amounts of GHGs in the atmosphere, not all gases are the same. Carbon dioxide is the most important one, because we still produce so much of it and it lasts for so long. The only way to stop its amount increasing is by reducing carbon dioxide emissions to zero. The only way to reduce the amount already in the atmosphere is by actively removing and storing it (e.g. by planting new trees).

Methane concentrations in the atmosphere on the other hand can be reduced simply by reducing its emissions. This means it doesn’t have to go to zero to halt climate change. But the lower it goes, the better for the climate, because the less warming there will be overall.

Comparing different greenhouse gases using a single metric

Some of the methane debate has focused on metrics, and how the various GHGs are measured and compared with each other.

The United Nations has adopted the Global Warming Potential (GWP) as the universal metric for reporting GHG emissions, and for measuring the success of mitigation. Most countries use this measure to compare emissions from different sectors, set overall targets, and inform emissions trading.

The GWP uses carbon dioxide (the most important greenhouse gas) as a reference, against which the warming effect of other gases can be compared. Emissions of each gas are reported as a “carbon dioxide equivalent” emission (sometimes abbreviated as ‘CO2-eq’).

The GWP is based on the amount of a single pulse (short burst) of carbon dioxide that would have produced the same cumulative warming effect over a given period as a single pulse of the gas being measured (such as methane). For instance, averaged over the course of a century, emitting one tonne of methane is estimated to have about 34 times the warming effect of one tonne of carbon dioxide (although in current accounting schemes, it is assumed to have only 25 times the effect; the change in number reflects our changing atmosphere as well as additional knowledge about the warming effect of methane).

There are valid criticisms of the GWP, and alternative metrics for these comparisons have been developed. However, none is perfect, as any metric that serves a particular policy purpose has shortcomings with regard to another one. New Zealand could chose to use a different metric for its domestic policy, but would still be expected to translate its overall emissions target into the metric currently used by the United Nations, namely the GWP.

Most importantly though, what target we set for GHG reductions by 2050 is a very different decision to what metric we use to compare individual emissions between gases year by year. A long-term target is where we want to get to; a metric is a tool that helps us get there.


One argument put forward during the current debate is that if we “stabilise” methane at current levels, this would put farmers in a “climate neutral” position. In other words, continuing methane emissions wouldn’t make the climate situation any worse — and hence they don’t pose a problem.

An analogy would be a dairy farmer who has allowed his cows to stand in the river for years. If the number of cows doesn’t change, then the pollution of the river won’t change in future either. Could this farmer reasonably claim to be now “pollution neutral” by keeping things unchanged?

Keeping methane at today’s levels may not make the climate much worse, but it would not make it any better either. The effects of increased methane inputs in past decades are still being felt. Less methane would be better for the climate. And the goals of the Paris Agreement, to keep warming to well below 2 degrees above pre-industrial levels, requires efforts from all sectors to minimise their contribution to overall warming as much as possible.

The Role of the NZAGRC

The NZAGRC is dedicated to developing technologies and practices which reduce the full suite of GHGs generated by agriculture, encompassing methane from both enteric (digestive) fermentation and manure management, nitrous oxide from agricultural soils, and the management of soil carbon.

We also co-ordinate New Zealand’s research to develop agricultural GHG emissions mitigation options in partnership with the industry-led PGgRc (the Pastoral Greenhouse Gas Research Consortium).

New Zealand’s research into reducing livestock greenhouse gas emissions concentrates on breeding low methane-producing animals, low-methane-producing feeds, reducing methane via a vaccine and using an inhibitor product, reducing nitrous oxide and building on efforts to reduce nitrate leaching on farms, and increasing carbon sequestered in soil.

An integrated systems research programme runs alongside the detailed methane, nitrous oxide and soil carbon research to quantify the contribution that farmers already make through their increased efficiencies and management options on farms.

The NZAGRC also leads New Zealand’s science input into the Global Research Alliance on Agricultural Greenhouse Gases, which was established to find global solutions to mitigate agricultural GHG emissions. This fosters international collaboration and helps build capacity in other countries to tackle their own GHG emissions.

Collectively, these efforts seek to ensure that livestock farming can continue to food security and livelihoods not only in New Zealand but globally, while enabling New Zealand and the world to meet the objectives of the Paris Agreement and keep climate change within manageable limits.

Source: New Zealand Agricultural Greenhouse Gas Research Centre

Author: Bob Edlin

Editor of AgScience Magazine and Editor of the AgScience Blog

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