Net methane: missed opportunity?

Greenhouse gases

Dairy farm environment consultant Steve Cranston welcomes Beef + Lamb NZ’s recently released Environment Strategy but believes it has missed an opportunity to brand New Zealand’s red meat products as ‘warming neutral’.

With an eye on the future, B+LNZ’s strategy was launched last month. In line with Government thinking, this includes carbon neutrality for the red meat sector by 2050 as one of its four goals. Work in this area will see B+LNZ working with red meat farmers in Catchment Communities on greenhouse gas (GHG) emissions, amongst other issues, on the development of a GHG calculator for farmers which is expected to be ready for delivery next year, continuing long-term mitigation options through the Pastoral Greenhouse Gas Research Consortium (PGgRC) and study of on-farm GHG management practices and development of SMART goals for GHG emissions, water quality and so on.

Methane cycle - NZAGRC
Methane is produced by microbes in the fore-stomach of ruminants, from the plants that animals eat. Methane is a relatively short-lived gas that decays back into carbon dioxide with a half-life of around 12 years. But, while methane is in the atmosphere, it makes a powerful contribution to the overall warming effect of GHG because it is much more effective at absorbing heat radiation than carbon dioxide. Source: NZAGRC.

Cranston’s argument is that the strategy uses the current logic for measuring methane, Global Warming Potential (GWP).

In order that gases can be ranked against one another, the United Nation’s Convention on Climate Change (UNFCCC) has adopted the internationally agreed reporting measure Global Warming Potential (GWP), which gives a CO2 equivalent (CO2-eq) rating for GHGs. While methane has a shorter life-span, decades, rather than the main and worrisome GHG carbon-dioxide that remains in the atmosphere for hundreds or thousands of years, it is a more powerful gas absorbing more heat and enhancing the CO2-induced climate warming.

When averaged over 100 years (GWP100), the contribution to climate warming from one tonne of methane is 25 times that of one tonne of carbon dioxide, the UNFCC has determined through the Intergovernmental Panel on Climate Change (IPCC). The GWP100 is the basis on which international treaties are being developed.

However, says Cranston, “This does not take into account the GWP100 metric has no correlation to actual warming.”

In his opinion, this is because the methane is only in the atmosphere for a limited period and is constantly being emitted and degraded simultaneously.

“What drives global warming is the volume of methane in the atmosphere at any one time,” he has written.

Cranston believes there are more advanced and accurate ways of measuring methane and is promoting a ‘net methane’ approach: “This is inflow minus outflow and will directly correlate to warming effect. This is how the government measures carbon dioxide so seems logical to me.”

He points to Victoria University’s professor of climate change David Frame who released a study recently co-authored by himself and colleagues from Victoria, Oxford and Reading Universities in the UK and Norway’s Centre for International Climate and Environmental Research. Cranston believes Frame has created a better way to use the GW100, factoring in the fact stable methane does not cause more warming. Frame’s work suggests that the current GWP100 method of calculation exaggerates the effect of methane emissions on warming.

“It’s a big step forward, but I’m still cautious of this approach. Also, it does not measure inflow versus outflow so cannot be used to prove warming neutral,” says Cranston. He is encouraging red meat farmers to support the Bill in the current consultations, selecting Option 2 (see below), the scenario that he believes will enable them to demonstrate warming neutral.

According to the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), however, keeping methane at today’s levels may not make the climate much worse, but it would not make it better either.

The NZAGRC leads New Zealand’s science input into the Global Research Alliance (GRA) of 50 member countries, which was established to find global solutions to mitigate agricultural GHG emissions.

NZAGRC director Dr Harry Clark maintains the effects of methane inputs in past decades are still being felt. He argues less methane would be better for the climate and, in addition, the goals of the Paris Agreement to keep warming to well below 2°C.

Metrics and targets

Dr Harry Clark
Dr Harry Clark.

NZAGRC acknowledges there are valid criticisms of GWP and that alternative mechanisms have been developed. However, it makes the point that any metric developed for a particular policy purpose has shortcomings with regard to another. While New Zealand could choose to use a different metric for our domestic policy, it would still be expected to translate its overall emissions target into the metric currently used by the UN, namely GWP.

Clark also makes the point that the targets set for GHG reductions by 2050 are very different to the measures used to compare individual emissions from year to year.

“A long-term target is where we want to get to; a metric is a tool that helps us get there,” he says.

Following advice given to the then National Government by Parliamentary Commissioner Dr Jan Wright in 2016, and continuing with the new coalition Government, New Zealand is moving to establish an independent Climate Change Commission, through a Zero Carbon Act. This will also set targets for 2050, including reducing the long-lived GHGs carbon dioxide and nitrous oxide and stabilising the short-lived methane.

Consultations recently opened on the proposed Zero Carbon Bill, which will lead ultimately to a decision by New Zealand’s Parliament on the path to take to tackle this country’s GHGs. This presents three broad scenarios for 2050 targets for New Zealanders to consider: 1) net zero carbon dioxide by 2050 which would reduce carbon dioxide emissions to zero by 2050, but not set a target for other gases like methane or nitrous oxide; 2) net zero long-lived gases (mainly carbon dioxide and nitrous oxide) and stabilisation* of short-lived gases (mainly methane) by 2050; and 3) net zero emissions by 2050, which would reduce net emissions across all GHGs to zero by 2050.

*NZAGRC notes ‘stabilisation’ could mean reducing methane emissions to a level lower than today.

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