Dr Jacqueline Rowarth: Split gas approach puts NZ ahead of the game

New Zealand showed leadership by adopting a split gas approach in 2019. File photo / Brett Phibs

Opinion: New Zealand agriculture once again leads the pack by adopting a split gas approach to tackle climate change back in 2019, Dr Jacqueline Rowarth writes.

New Zealand is ahead of the game. Again.

In 2021 the IPCC (Intergovernmental Panel on Climate Change) concluded that when several gases of different longevities were being considered, estimates of contribution to surface warming would be improved by using either of two new metric approaches “or by treating short and long-lived GHG emissions pathways separately”.

The new emissions metric approaches were GWP* (which accounts for a change in global surface temperature that arises from a change in the emission rate of the short-lived gas) and the combined-GTP (global temperature potential CGTP, indicating the temperature change at the end of a given time period relative to CO2).

These metrics have been developed to relate emissions rates of short-lived gases to cumulative emissions of carbon dioxide. The authors of the report concluded that treating short-lived GHG separately was appropriate.

New Zealand adopted the split gas approach in 2019, allowing short-lived methane to be treated separately from the longer-lived gases. This was a result of explanation and advocacy by Federated Farmers and the levy groups. At the same time, ongoing negotiation on targets was agreed.

New Zealand again showed leadership while the global debate continued.

The split gas approach acknowledges that methane does not have to reduce to zero to reduce global warming.

For New Zealand, it also recognises the fact that New Zealand’s methane emissions per kilogram of product are low, that animal protein containing human-accessible essential amino acids is important for human nutrition, and that the export economy depends upon the primary sector.

The Climate Change Commission appears to have accepted some of these arguments.

Its draft advice to the government released earlier this year focuses on non-biological emissions (industry and fossil fuel use) and mentions not only “intensity” of emissions, but also ”leakage”.

“Leakage,” as Federated Farmers of New Zealand has been hammering, is the reality that if efficient countries reduce production to reduce emissions, and that production is picked up elsewhere in countries with a higher GHG footprint, the world is worse off.

A paper published in Nature last year, authored by 33 researchers in the climate field, including two from New Zealand, urged countries to adopt separate reduction targets for long-lived and short-lived gases.

Dr Jacqueline Rowarth. Photo / Supplied

New Zealand’s Climate Change Response (Zero Carbon) Amendment Act 2019 does this by setting the goals to:

• reduce net emissions of all greenhouse gases (except biogenic methane) to zero by 2050
• reduce emissions of biogenic methane to 24–47 per cent below 2017 levels by 2050, including 10 per cent below 2017 levels by 2030.

The primary sector is on track to achieve its 2030 goal through increasing efficiencies (productivity gains) on-farm and responding to the market forces that have reduced animal numbers as horticulture, forestry and housing have expanded.

While arguments continue globally about how much the ongoing reduction needs to be, the fact is that farmers and growers are already on to it – doing what they can while staying economically viable.

Although there are speakers saying that methane doesn’t matter, the Parliamentary Commissioner for the Environment has explained why it does.

Also at play are politics, nationally and globally, as well as economics and science.

Trade is implicated: the EU is bringing in a “carbon border adjustment mechanism”. Other countries and jurisdictions are likely to follow, whilst juggling their reporting in GWP100. The IPCC allows other metrics to be used as well, but GWP100 is the requirement.

Confusion around reporting arose because the IPCC papers are released at various stages of completeness.

In March this year, the summary report of the sixth report (first published in 2021), a longer report and various annexes and press releases, but not yet (as of mid-June) the full report was published. The summary report can be cited but is still subject to copyediting and layout.

Prior to March, draft reports were published with “do not quote” warnings – but this hasn’t stopped people from doing so, and the result has been increased confusion.

The summary report uses only GWP100 (a measure of the heat absorbed over a given time period due to emissions of a gas), but states that “The choice of metric depends on the purpose of the analysis”.

Further, it explains that “all GHG emission metrics have limitations and uncertainties, given that they simplify the complexity of the physical climate system and its response to past and future GHG emissions”.

Part of the complexity is that gases behave differently according to the concentration of those around them.

Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:

Appropriate metrics for measuring the impact of GHG and feeding numbers into models with constraints and assumptions will continue, but New Zealand is ahead of the game with the split gas approach.

New Zealand farmers are also leading with low emissions per kilo of product – which is what customers and consumers say they want.

We’re ahead of the game there as well.

- Dr J.S. Rowarth, Adjunct Professor, Lincoln University, has a PhD in soil science from Massey University and is on the board of directors of DairyNZ, Ravensdown, Deer IndustryNZ and NZ Animal Evaluation Ltd. The thoughts and analysis presented here are her own. jsrowarth@gmail.com