Mike Cranstone

Whether a greenhouse gas's lifespan is just decades or centuries results in a significant difference in its contribution to global warming.

New Zealand emits three main greenhouse gases. Carbon dioxide and nitrous oxide are long-lived, so every kg produced today will have a warming effect every year for centuries to come, this is why they are also referred to as stock pollutants, as the effects constantly build up in a stock.

Methane, however, is a short-lived gas, and has a half-life of 12 years, this is why it is referred to as a flow pollutant as the effects need to take into account the flow of methane in and out of the atmosphere. Unlike the long-lived gases of carbon dioxide and nitrous oxide, methane does not need to be reduced to a net zero level to have no additional effect on Climate Change. Rather a target of reducing New Zealand's methane emissions by 10-22 per cent by 2050 is sufficiently in ensuring the agriculture sector does not contribute to additional warming through methane emissions.


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This research is widely accepted in the science community, and how it is implemented into policy is critical for the New Zealand economy. Prof. David Frame from the Climate Change Institute based at Victoria University is working with many other scientists from University of Oxford in UK.

They have rejigged the GWP100 model, and their GWP* model now recognises not only the warming effect of each gas, but also how long each gas produces a warming effect for.

Methane makes up 35 per cent of New Zealand's GHG - but, importantly, since 1990 agricultural methane levels have only increased by 4.4 per cent.

The other two gases are still a significant challenge for agriculture.

Nitrous oxide is a long-lived gas and is produced from urine patches and nitrogenous fertilisers. The levels have risen by 27 per cent since 1990. Transport and energy are NZ's main contributors of carbon dioxide, these are relevant to agriculture too with an increase of 35 per cent.

To put this in context, New Zealand's overall greenhouse gas emissions have increased by 54 per cent since 1990.

We must remember what we are trying to achieve, The Intergovernmental Panel on Climate Change has set an ambitious target of restricting global warming to 1.5 degrees by 2050. Our Government has set a national goal of reducing greenhouse gas emissions to half of 1990 levels by 2050.


To achieve this aspirational goal, carbon dioxide and nitrous oxide emissions need to stop. However, methane emissions need just to be reduced and stabilised, with a reduction of 10-22 per cent by 2050. Agriculture may well achieve further reductions, but the cooling effect of these must be recognised for the benefit of agriculture and as an entire country.

The cooling effect from reducing methane levels is a one-off gain. Although significant, the timing of this is shown to not have any influence of peak global temperatures as long as it occurs before this peak of global temperatures occurs.

New Zealand agriculture is investing more than $100 million into methane-reducing research, and have promising results reducing the methane production from ruminants. A vaccine, feed additives and different forages and genetics are all possibilities but are at least eight years away from commercial release. Without this mitigating technology, agriculture has very few options for reducing its methane emissions, since it is a natural biological process.

Let's give this research a chance. Supporting this research may reduce our methane emissions without devastating the NZ economy, and unlike measures that simply reduce the New Zealand livestock industry, these cutting-edge technologies have the ability to be exported, and to make a huge impact on global livestock emissions. That is real global leadership.

Mike Cranstone is Federated Farmers Whanganui provincial president