Emerging conflicts

Greenhouse gas intensity versus total emissions

Recent FAO reports show that world food demand is increasing, with a lack of basic supply resulting in hunger in some regions and changing food demand due to increasing affluence in other regions. The rate of productivity growth in agriculture is predicted to decrease from 2.3 per cent between 1961 and 2000, to 1.5 per cent between 2000 and 2030, and further to 0.9 per cent between 2030 and 2050 (FAO, 2009). In contrast, the number of people dependent on each hectare of arable land is predicted to increase from 2.4 to 4.5 and 6.4 over the same periods (FAO, 2009). In short, the world needs more protein and this requires a given amount of N input to produce. Whilst we can improve the efficiency of N conversion and potentially reduce N2O emissions per unit of production, total N use in agriculture will need to increase to produce the protein needed to feed a growing world population. This inevitably means an increase in total global N2O emissions. The primary food producers only have control over the efficiency per unit of production and we may need to design policies that reward increased food production with an acceptable greenhouse gas emission intensity. A decrease in greenhouse gas intensity can either be achieved by improving the efficiency of a livestock sector, or by putting more emphasis on livestock sectors with inherently low greenhouse gas emissions per unit of product. For example, Verge et al (2008, 2009) estimated that total greenhouse gas emissions for beef production in Canada was ~10kg CO2-eq per kg of live weight, while those for pork production were ~ 2kg CO2-eq per kg of live weight.

These greenhouse gas emissions intensity arguments are likely to be tabled in future World Trade talks, for example looking at where to produce food with the lowest carbon footprint. In parallel, research should continue to focus on improving the efficiency of conversion of nutrient N into products, whilst minimizing N2O losses, as efficiency gains obtained with current N2O mitigation strategies are not likely to be able to match the rate of productivity increase expected.

Mitigation and climate change adaptation

In many parts of the world, future climate change projections show warmer winters with increased growth potential, but drier summers with more variable rainfall and extreme heat (for example Cullen et al, 2009). A logical adaptation to this changing environment would be to increase N fertilizer applications in the warmer winter period, thus compensating for reduced summer production. However, it is obvious that this strategy could well increase total N2O emissions. Thus there are a number of possible emerging conflicts between strategies for adapting to a changed climate as opposed to strategies to reduce total N2O emissions. To avoid these conflicting messages to producers requires both mitigation and adaptation outcomes to be considered when developing policy and farmer advice.

Recognition ofon-farm mitigation in nationalinventories

To credit countries for adoption of mitigation strategies, their effect on the N2O inventory needs to be accounted for. Analogous to the adoption of country-specific EFs, the incorporation of mitigation options into the IPCC inventory methodology is subject to scrutiny by international expert review teams (ERTs). The ERTs will judge the soundness of the assumptions and assessment based on scientific evidence. However, the current structure of the IPCC methodology, i.e. estimating N2O emissions from the size of N inputs in the system multiplied by an EF for each input, requires these EFs to be determined under relatively controlled conditions, so that the effect of a mitigation strategy on N2O emissions from each source can be separated. However, these controlled conditions are not likely to represent the full farm system and care should be taken when translating the results of these controlled experiments into a whole system's response to a mitigation strategy. To fully understand the impact of a mitigation strategy and to appropriately account for this impact on inventories requires a combination of experiments under controlled conditions, determining the effect of EFs individually, coupled with field measurements and/or modelling at a paddock or farm level to fully understand the whole system's response to these strategies.

This highlights the importance of farm-scale inventory methodologies to underpin an agricultural emission trading scheme (ETS). Both Australia and New Zealand intend to impose a form of emissions constraint on their agricultural sectors, to assist with meeting the current and future emissions reduction targets. Currently the imposition of an ETS on agriculture is limited by lack of appropriate and agreed measurement and estimation methods. Australia's National Carbon Accounting System (NCAS) accounts for greenhouse gas emissions from land-based sectors. The NCAS includes an IPCC Tier 3 modelling framework that combines remote sensing of land cover change, land use and management data, climate and soil data, greenhouse gas accounting tools, and spatial and temporal ecosystem modelling (FullCAM), which also includes algorithms for accounting for N2O spatially. However, it is critical that these spatial inventory methods

• align with actual on-farm mitigation action,

• are sufficiently flexible to incorporate new mitigation practices,

• use methods that are agreed by both policy and farmers alike,

• are easy to use and do not incur significant costs of compliance to farmers. Failing to achieve this is likely to result in farmers deliberately working to undermine the system, misguided mitigation efforts and significant increases in transaction costs associated with the implementation of ETS policy.

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