Primary Industry: Greenhouse gases (GHG) are essential for life on earth. Although they make up only a small fraction of our atmosphere, due to their "heat trapping" ability they represent the difference between the world being an almost lifeless planet of minus 19°C and the comparatively comfortable one we live in today of about 14°C.
However, it is possible to have too much of a good thing and there is now robust scientific evidence that the climate is changing, and that most of the warming observed over the past 50 years is due to increasing GHG concentrations in the atmosphere arising from human activities.
Agriculture, in common with other industries, emits GHG in the form of CO2 arising from the burning of fossil fuels for the running of farm vehicles and machinery and electricity generation. However, agriculture's largest source of emissions are in the form of methane (CH4) and nitrous oxide (N2O) arising from raising livestock and growing crops.
Methane is emitted from the mouths of animals as a by-product of the digestion of feed, from the storage and handling of animal wastes and from rice production. Nitrous oxide is emitted when nitrogen-containing fertilisers and manures are spread on the land and from urine patches deposited on land by grazing animals. Worldwide it is estimated that about 13% of all human produced GHG emissions arise from agricultural emissions of CH4 and N2O.
New Zealand is in a unique position among developed countries in that its economy is still heavily influenced by agriculture, particularly pastoral agriculture; in 2012 the value of exports from the pastoral sector were $19.7 billion, 42% of total exports. The importance of the pastoral agricultural sector to the New Zealand economy is also reflected in our GHG emissions.
Currently agriculture accounts for 47% of New Zealand's total carbon dioxide equivalent emissions and emissions have risen by approximately 12% since 1990. Ambitious output targets from the dairy and meat sectors suggest that emissions from agriculture will continue to rise in the future.
Agricultural GHG mitigation research
Reducing CH4 and N2O from emissions agriculture is scientifically challenging. They arise from natural microbial processes that have multiple influences, some of which are difficult to control. For example, the amount of N2O emitted from urine deposited on pastures by grazing animals is heavily influenced by rainfall. In addition, any control measures cannot be at the expense of reducing agricultural productivity. Methane emitted during the digestion of feed plays an important role in ensuring that the digestive process works efficiently.
In the past ten years successive New Zealand governments and the agricultural industry have invested in research to reduce GHG emissions. Broadly, the research can be divided into two types, 'indirect' and 'direct'.
Indirect research is research designed to improve the efficiency of agricultural production, for example breeding cows with improved milk yields and sheep with better lambing rates. Although not targeted at reducing GHG emissions, improvements in the efficiency of production do influence emissions as they result in more product being produced relative to the amount of GHG emitted. Improvements in efficiency have resulted in emissions per unit of product falling by an average of less than 1% per year since 1990, a substantial achievement and one that makes New Zealand one of the lowest producers of agricultural GHG emissions per unit of milk and meat produced in the world.
Although these achievements are significant, they are not enough on their own to reduce absolute GHG emissions given that industry targets are to increase product output by close to 2% per year. This is where direct mitigation research comes in. Direct research aims to reduce the amount of GHG emitted per kg of feed eaten or kg of nitrogen applied, irrespective of the amount of product produced. Both direct and indirect approaches are needed for agriculture to contribute to reductions in absolute GHG emissions.
The New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) focuses its research on direct emissions reduction. In partnership with another government industry entity, the Pastoral Greenhouse Gas Research Consortium (PGgRc), we focus on reducing emissions of CH4 and N2O and also on exploring whether it is possible to offset these emissions by taking CO2 from the atmosphere and storing it as stable carbon in soils.
In the CH4 area our main effort has been in trying to reduce emissions arising from the digestion of feed in ruminants. The type of feed eaten influences the amount of CH4 produced, for example brassicas produce 20% less CH4 than grasses, and an attractive method of reducing emissions is to change the feed. However, this is not simple in practice in New Zealand when many animals graze outdoors all year. A more practical approach is to try to suppress the organisms that are responsible for producing methane in the animal.
One method being researched is to vaccinate animals so they produce compounds in their saliva that can suppress the growth of the methane producing organisms. Another promising area is discovering safe and effective compounds that can be fed in slow-release form to directly reduce the activity of these methane emitting organisms. Both of these approaches have progressed through the laboratory stage and are being tested on small numbers of animals under highly controlled conditions.
Nitrous oxide emissions from urine patches and nitrogen fertiliser applications can be reduced by the application of a group of compounds called nitrification inhibitors. Various types of inhibitor have been tested and the results are highly promising. Combined with managements designed to reduce the quantity of nitrogen applied to soils, especially in wet conditions, they offer a good technical solution. However, for widespread uptake their cost needs to come down and they will need to go through the appropriate product safety and regulatory processes.
Storing more carbon in soils is appealing as a mitigation approach. New Zealand soils are high in soil carbon (150 - 200 tonnes per hectare down to a depth of 30cm) and adding just one tonne per hectare per year would offset all agricultural emissions annually.
However, although the general principles of how to store more carbon are known (put more carbon rich material into the soil), translating this into carbon that is stored in a stable form is more difficult, and current evidence suggests that some of our highly productive land is actually losing soil carbon.
The NZAGRC is undertaking a major on-farm study in the Waikato to explore ways of practically increasing soil carbon and early results suggest that using plant species that put more carbon into their roots can increase the total amount of soil carbon stored.
Climate change is a long-term issue and addressing the drivers of climate change, GHG emissions, also has to be viewed in the same way. Although it is appealing to think that a 'silver bullet' solution is just around the corner, it is perhaps more realistic to think in terms of incremental progress in a number of areas combined into 'baskets' of approaches that can bring about substantial reductions in the long term.
Harry Clark is the director of the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) and co-chair of the Livestock Research Group of the Global Research Alliance for Greenhouse Gases.
He is a lead author for the International Panel for Climate Change Fifth Assessment Report (AR5), sits on the FACCE-JPI Science Advisory Board, is a member of the Australian Filling the Research Gap expert advisory panel and is technical advisor to the New Zealand Global Partnerships for Livestock Emissions Research Fund.