FAQs: The role of methane

Methane is a short-lived greenhouse gas that contributes to warming our climate. It is known as a 'trace gas', which means it’s only around in small concentrations – but it has a large impact on climate change. 

Most methane emissions in Aotearoa New Zealand are 'biogenic' in origin, meaning they are produced from living things and processes.  Of our methane emissions, 91% of biogenic methane comes from ruminant animals in agriculture, and 9% comes from organic waste breaking down in landfill.

Non-biogenic methane emissions are also leaked during oil and gas extraction. While this proportion is small in Aotearoa New Zealand, it is more significant for other countries. This is important to consider when broad international statements are made about reducing methane emissions, such as the pledge Aotearoa New Zealand signed up to at COP26 to reduce global emissions by 30%.   

Methane behaves differently in our atmosphere compared to carbon dioxide. While CO2 (carbon dioxide) and N2O (nitrous oxide) stay in the atmosphere for hundreds of years, and are considered ‘long-lived’ gases, methane only stays in the atmosphere for a couple of decades and is considered to be a ‘short-lived’ gas. The targets we have in Aotearoa reflect the different nature of these gases.   

To stabilise global temperatures, we need to significantly reduce emissions of greenhouse gases (GHGs) into our atmosphere. To limit warming to 1.5°C above pre-industrial levels, ‘long-lived’ gas emissions need to reach net zero by 2050 – and potentially hit negative figures in the second half of the century. Methane emissions still need to reduce and stabilise at some level – the question is, by how much?   

Metrics are often used to simplify how we compare the climate impact of different gases to that of carbon dioxide – i.e. their “carbon dioxide equivalence”. Metrics simplify the complicated physics, chemistry, and biology in the full models used by the IPCC for their assessment reports and for the global 1.5°C report.  The Emissions Trading Scheme and the national Greenhouse Gas Inventory are two examples of where metrics are used in New Zealand.

Different metrics are useful for different things.  Each has its own strengths and weaknesses depending on the purpose it’s being used for.

Given the challenges in using metrics to compare the impacts of different gases, it’s important to keep in mind the purpose of using a  metric. If the purpose is to assess the warming impact of emissions, the best approach is to consider the warming impact of each individual gas rather than use an equivalence metric.

Science can help answer some of that question, but only gets us so far. Science is also evolving in this space, as the Intergovernmental Panel on Climate Change (IPCC) report released on 4 April 2022 shows. It has found that deep greenhouse gas emissions reductions by 2030 and 2040, particularly reductions of methane emissions, lower peak warming, reduce the likelihood of overshooting warming limits and lead to less reliance on net negative CO2 emissions that reverse warming in the latter half of the century.  

The IPCC have summarised the science and are clear that to limit global warming to 1.5°C, global long-lived gas emissions need to reach net zero by 2050, while global biogenic methane emissions will need to reduce by 24-47% from 2010 levels by 2050.    

To reach global targets, the world could collectively invest more in reducing long-lived gas emissions, which would mean that biogenic methane emissions would not have to reduce as much. Conversely, we could globally invest more effort in reducing biogenic methane emissions, so long-lived gas emissions can reduce at a more measured pace.  

There is no question that we need to take action on biogenic methane. Research from the New Zealand Agricultural Gas Greenhouse Research Centre shows that biogenic methane emissions have been the largest contribution to global warming in Aotearoa since 1840, aside from deforestation. Even if we achieve our 2050 targets, methane will still have been our largest contributor to global warming. 

The NZGARC research states "New Zealand’s biogenic methane emissions currently make a bigger estimated contribution to global warming than cumulative emissions of fossil carbon dioxide and nitrous oxide combined. If gross emissions of those three gases continued at current rates, biogenic methane would remain New Zealand’s largest single contributor to global warming for the next six decades despite its relatively short lifetime in the atmosphere compared to carbon dioxide and nitrous oxide."  

The science only gets us so far because there are also value judgements that need to be considered, such as how quickly should Aotearoa reduce emissions relative to other countries.  

There are value judgements in many areas – not just reducing biogenic methane.  In transport, for example, some of those value judgements are around questions such as “how should Aotearoa spread its investment across encouraging more people to buy or drive EVs, developing public transport, and increasing active transport like cycling and walking?”

These value judgements are important for Aotearoa, and they involve assessing a range of things – for example our historic responsibility because as a country we’ve had relatively high greenhouse gas emissions (including methane) compared to most other countries, particularly the developing world. Developed countries are encouraged to ‘take the lead’ on climate action.  

Decisions on the emissions targets for Aotearoa New Zealand sit with the Government of the day, as do the value judgements that are needed, as these need to reflect the democratically expressed views of the country.

The Climate Change Response Act 2002 sets out clear processes and responsibilities for both the Commission and Ministers. 

Our role is to provide independent and evidence-based advice that can be considered by Government, and that can help inform the public.

In our 2024 review of Aotearoa New Zealand’s 2050 emissions reduction target, we provided independent, expert advice on whether the target should be changed, according to criteria set out in the Climate Change Response Act. Our review found that there had been significant changes since the target was set in 2019, and these justified a change to the target. As required, the Commission made a recommendation on what the new target should be. Read more about this report.

The term ‘no additional warming’ is sometimes used to describe an approach that aims to stabilise the global warming due to biogenic methane emissions at current/recent levels, rather than reducing biogenic methane emissions and their associated warming effect.

Taking a ‘no additional warming’ approach to set a biogenic methane emissions target would require judgements about the: 

• reference year – when ‘no additional warming’ would be measured from (ie why this year, rather than that year?)
• levels of observed and expected background (global) methane emissions – the warming caused by domestic biogenic methane emissions depends on global background emissions (ie how much methane will be in the atmosphere already in the future). Global methane emissions are hard to predict.
• level of acceptable risk – for the possibility that the biogenic methane emissions target does not limit the warming it causes as much as intended.

Science cannot tell us what reference year to choose to contribute to global efforts to limit warming to 1.5°C. Different choices about the reference year and background emissions scenarios mean that the required biogenic methane emissions level consistent with a ‘no additional warming’ approach can vary widely.

One study that varies the reference year (from 1984 to 2017) and background emission scenarios suggests Aotearoa New Zealand’s biogenic methane emissions would need to reduce by 14–58% from 2017 levels to achieve ‘no additional warming’ by 2050.

Through our call for evidence and during consultation for our 2024 review of the 2050 target, many submitters suggested we should adopt ‘no additional warming’ as a principle for our recommendation on the biogenic methane component of the 2050 target.

However, based on the evidence available to the Commission, we concluded that a ‘no additional warming’ approach for biogenic methane that resulted in a less ambitious methane target than the current one would not adequately contribute to global efforts to limiting warming to 1.5°C above preindustrial levels, as required under the Climate Change Response Act.

Setting targets according to no additional warming from biogenic methane would require trade-offs and create consequences.

If applying the principle of ‘no additional warming’ resulted in a less ambitious target for biogenic methane reductions than the current 2050 target, Aotearoa New Zealand would face choices. It would have to:

• require faster and further reductions of other greenhouse gases to maintain (or reduce) the current target, or
• set a new target that allows more warming than the current 2050 target.

In June 2024, the Government commissioned a ministerial advisory panel to review methane science and the 2050 target, focused on determining the level of biogenic methane emissions that would be consistent with ‘no additional warming’ beyond 2017 levels. This panel was separate from the Commission. More information about the panel and its report: Review of methane science and target | Ministry for the Environment.

This review was separate to our comprehensive review of the 2050 target, which also took place in 2024 and was carried out according to criteria set out in the Climate Change Response Act.