Greenhouse gases include carbon dioxide , methane , nitrous oxide and water vapour.
They absorb heat from sunlight, demonstrating a global warming potential (GWP) for each gas. Elevations in GHGs occur following the combustion of fossil fuels such as coal, oil and gas, to energise an ever energy-hungry planet.
In the past 200 years, there has been ever-increasing emissions of GHGs. In the past 30 years, temperatures globally appear to have reached a tipping point affecting global water cycles, causing more frequent severe droughts, forest fires, tornadoes and floods. Atmospheric rivers form in the equatorial regions where the warm air becomes saturated with vapourised water.
Vapour-laden air flows into cooler temperate regions where the water vapour condenses to cause tropical storms, flooding and tornadoes.
The United Nations Framework Convention on Climate Change (UNFCCC), involving 197 countries, was set up in 1992 to monitor climate change while Annual Conference of Parties (COP) meetings began in Berlin in 1995. The COP3 meeting in Kyoto in 1997 developed an emissions trading scheme in which GHG emissions, largely from fossil fuels, were measured and costed.
Emissions could be abated using credits issued by the Government or by planting exotic forests, to sequester carbon. The Paris (2015) Accord expanded the scope to earn carbon credits from exotic forests, to include indigenous forest and bush, pasture, soils and oceans.
This was a pivotal development for agriculture which could produce emissions or generate credits. By contrast, industry could incur losses without the ability generate credits.
Overall, the accord has been a relative failure because GHG levels have increased since 2015. With current policy in place, climate will increase by 2.40dgeC, rather than the 1.50degC increase specified in the Paris Accord.
A Nationally Determined Contribution (NDC) was agreed in Paris so that each country could prepare, communicate and maintain NDCs that it intends to achieve, reaffirming that individual countries should submit annual NDCs.
NDCs are critical to highlight how small nations such as New New Zealand can advance strategies for GHG emissions, that may vary substantially from other developed countries.
As an example, 80% of the UK’s energy is generated by fossil fuels, while 80% of New Zealand’s energy comes from renewable, non GHG-emitting hydro, solar or wind energy, reducing our reliance on
CO2-emitting fossil fuels.
Because New Zealand’s economy is based on agriculture, its GHGs are derived primarily from biogenic (plant/animal) sources, resulting in high methane (NZ-44% v UK-12%) and low carbon dioxide (NZ-43% v UK-80%).
Carbon dioxide
New Zealand is rich in natural capital (vegetation) and renewable biomass, while photosynthetic plants convert CO2 to soil organic carbon (SOC) at very high (5-6%) levels.
New Zealand’s fertile soils, extensive vegetation, moderate climate, sunshine and rainfall produce one of the most photosensitive ecosystems globally.
This has evolved to capture and sequester atmospheric CO2 as SOC. There is evidence biodiverse pasture may be as efficient in capturing carbon as forests.
Increased SOC levels not only increase carbon storage, but improve soil fertility, water porosity and storage and prevention of soil erosion.
Soil is the richest reservoir of carbon on the planet and SOC levels can be reduced or increased by land use change (LUC).
As New Zealand pastures and forests produce some of the largest natural capital, farmers have the potential to use LUC to increase SOC , remove CO2 by photosynthesis and sequester methane emissions and nitrous oxide.
The use of regenerative agriculture practices, with minimal input of synthetic fertilisers or agrochemicals, and pasture management through adaptive grazing can create farm systems where healthy SOC rich soils act as GHGs sinks.
The recent report from the New Zealand Interim Panel on Climate Change ( NZiPCC) on strategies to mitigate climate change in New Zealand did not recommend sequestration of carbon in soil to remediate GHGs.
Its suggested reliance on reducing sheep and beef numbers, to be replaced by indigenous and exotic trees, failed to appreciate that an investment in agroforestry involving indigenous trees, shrubs and riparian planting, may be a more effective way forward for balanced land use.
Considering New Zealand has almost unlimited capacity to generate plant biomass and build soil organic carbon, it is surprising that NZiPCC ignored ways by which holistic or regenerative farming might mitigate CO2 and N2O emissions in SOC-rich NZ soils.
The suggestion that regenerative agriculture could not be endorsed was based on their assessment that there was no robust data available.
It would be a serious omission if future NDCs from New Zealand exclude regenerative agriculture, when considering land-use changes.
Perversely, all that may be necessary to make New Zealand net carbon zero by 2050 is to reconstitute natural farming practices using the sustainable pathways nature has predestined.
Methane
The predominance of methane among New Zealand GHGs (43%), makes it the signature GHG in NZ. By comparison, no developed country worldwide has methane levels greater than 15%, and most have below 10%.
While biogenic CH4 produced by organic waste or enteric emissions from animals/plants is found at high levels in New Zealand, it could be managed cost-effectively by changes in farming practices that reduce methane emissions.
Methane has a significantly (20X) higher global warming potential (GWP) than carbon dioxide because it is a short-lived flow gas with a half-life of 9-12 years. A short-lived flow gas reaches an equilibrium for a given system where the amount emitted balances the amount removed.
A major reason for the short half-life of methane may be that biogenic methane is inactivated naturally by hydroxyl molecules.
By contrast , methane from fossil fuels used in industry may not inactivated so efficiently, as hydroxyl molecules are not produced in vegetation free industrial areas, where methane molecules may escape more easily into the atmosphere, and may persist for 12 years.
In this regard, the impact of individual GHGs on climate extremes relates not only to their rate of emission, but also to their atmospheric stability and bioactivity.
Farm systems in New Zealand
In order to develop an emissions-trading scheme for agriculture, precise metrics must be developed to monitor, measure and differentiate GHGs emitted from industry, transport and agriculture sectors. Considering the assays involve measurements of gas levels in model capture systems, there is considerable uncertainty and possible error associated the estimate of emission levels of all of the GHGs.
In addition there could be major error associated with its function where each GHG has different global warming potential.If an ETS scheme is to be linked meaningfully with climate change, accurate metrics must be used to monitor individual GHG levels and their GWP. The relatively high levels of methane found in New Zealand signifies that the metrics around methane measurements must be accurate or our ETS scheme may be seriously compromised.
