New Zealand's unusual carbon profile marks it apart from other countries trying to lower greenhouse emissions

New Zealand is facing a Gordian knot in the politics of climate change. The Prime Minister’s Chief Science Adviser Professor Sir Peter Gluckman, opening the Agricultural Greenhouse Gas Mitigation Conference in Palmerston North at the end of April, explained that irrespective of what happens in terms of international agreements, New Zealand faces ‘domestic and diplomatic challenges because our own emissions mix is both high in per capita terms and unusual in terms of its profile’.

In contrast to most developed countries, New Zealand’s emissions are dominated by animal-derived methane and nitrous oxides. We also have what Sir Peter describes as ‘complex transport issues both domestically and because of our geographic position on the globe.’ In addition, he says that “Our already high renewables profile and the absence of heavy industry leave us with little choice but to focus on mitigation within agriculture”.

The new agreement on climate change is expected to be adopted at the Paris Climate Conference in December this year, with implementation from 2020. The aim is another protocol, which is being negotiated through a process known as the Durban Platform for Enhanced Action. Jo Tyndall, New Zealand Climate Change Ambassador, explained to conference delegates that there is strong political will to achieve results. President Barack Obama has already indicated that he aims to lead the world to a historic climate change agreement. Of importance to New Zealand is that the Paris talks are likely to include all sectors and all gases.

New commitments to reduce greenhouse gases are being requested based on scientific evidence, and New Zealand is doing its part in the research. The New Zealand Agricultural Gas Research Centre (NZAGRC) based in Palmerston North leads New Zealand's science input into the Global Research Alliance on agricultural greenhouse gases.

The discovery of five compounds (out of more than 100,000 tested) which reduce rumen methane production by 30-90% was announced at the conference. The news is exciting for scientists, but testing has not yet occurred in the field, and the cost, mode of delivery, and the potential for unintended impacts have yet to be explored.
While the science continues on these compounds, other possibilities are also being examined including breeding lower emitting animals, the effect of diet on emissions, and the development of vaccines.

But good things take time. In his opening address, Sir Peter suggested that we are facing a 20-30 year road to transition ‘because the science is very hard and will be slow to translate to application for a number of reasons’. Perhaps of most importance, “The nature of biological evolution and in particular the co-evolution of the ruminant and its gut bacteria mean that changing the ruminant’s’ methane profile is not simple either conceptually or technically”.

He also stressed that New Zealand’s economic profile and the role of the primary sector means that research in both mitigation and adaptation is critical. Naturally part of the research includes sequestration options, and soil organic matter is part of the mix. The argument is that soil organic matter holds carbon out of the atmosphere in the same way that trees do. All green plants remove carbon from the atmosphere during photosynthesis. As long as they are increasing in size the net gain means carbon is being removed. When they reach full size, e.g. a mature tree, carbon is being taken up at the same rate as it is lost -- there is no net sequestration.

The flows of carbon through grazed grassland are large, but of the carbon fixed in photosynthesis nearly half is respired (returned to the atmosphere as carbon dioxide) by shoots and at least half of what remains dies. Material that is not consumed by animals eventually dies and, with root material, can lead to a substantial amount of carbon sequestration in the soil. The amount of carbon sequestered below grassland has been estimated to be equivalent to that below tropical and temperate forests.
However, whereas trees are relatively easy to measure in terms of how they grow and mature, soil carbon is not.

At the Climate Change Mitigation Conference, Lincoln University’s Professor Frank Kelliher explained that ‘like planting trees, carbon soil stocks can offset greenhouse gases and take decades to accumulate’. He also pointed out that every 1.6 litres of petrol burned created 1kg of carbon emissions. “To offset one million tonnes of carbon would require an increase in soil carbon stock by one tonne of carbon per hectare over one million hectares”, he said. “But for every one tonne of carbon sequestered in organic matter, there is a cost in terms of nutrients -- $200 of nitrogen, sulphur, potassium, phosphorus…”

An additional concern is that New Zealand soils have relatively high amounts (or stocks) of soil carbon. In Australia soil carbon is typically less than 1% whereas in New Zealand pastoral soils are generally around 5%. However, the very nature of ‘hotter and drier’ means that those stocks are fragile. Deserts have very low stocks of carbon because soil micro-organisms scavenge whatever is available and plants are restricted in growth before the micro-organisms. Each drought experienced means that soils lose carbon, but within a pastoral system it is difficult to identify the drivers of change and the timeframes over which changes occur. The problem is that many changes in pasture management alter several factors simultaneously. Hence if some factors alter soil carbon in opposite directions, the ensuing observations, even after the decade or more it might take to get a measurable change in soil carbon, might give confusing indications.

An example is that few farmers would add fertiliser without increasing stocking rate and hence pasture consumption. Adding fertiliser alters not only the amount of carbon flowing to soil (if it increases total plant growth), but also the proportion of carbon partitioned to roots; it also alters the ‘quality’ (for example the carbon-to-nitrogen ratio) of all the material cycling in the system.

A further complication is the difficulty in measuring soil carbon sequestration. The process is slow, changes are small and measurement techniques aren’t sensitive, and spatial and temporal changes in total soil carbon can contribute to errors in measurement.

Despite proposals in, for instance, America and Australia, no country has yet implemented a successful soil carbon policy. Lack of success reflects lack of financial evidence of mitigation methods, the difficulty of measurements and the spatial variability of results inhibiting justified large scale actions and enforcements. A review of policies by NZAGRC summer research student Alex Tressler concluded that agricultural soil carbon should not be included in any policy: ‘filling the gaps in the research is essential before any enforced actions take place in order to protect New Zealand’s competitive advantages for agriculture, the economy, our society and the environment’.

Sir Peter has said that he doubts any magic bullets will exist. “Climate change is the arch-typical example of what is called post-normal science. This is a science involving complex systems where there will inevitably be uncertainties with some facts in dispute -- a high public values component, and a recognised urgency for action.”
Gordian knots require bold action. Basing that action on scientific research improves chances of success, and that research is under way with New Zealand leading the charge for agriculture. The NZAGRC is in pole position to create change for the benefit of New Zealand and the world.