Climate Change: Agricultural Mitigation

Climate Change: Agricultural Mitigation

Climate Change: Agricultural Mitigation M van Noordwijk, Jalan Cifor, Bogor, Indonesia r 2014 Elsevier Inc. All rights reserved. Glossary Adaptation ...

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Climate Change: Agricultural Mitigation M van Noordwijk, Jalan Cifor, Bogor, Indonesia r 2014 Elsevier Inc. All rights reserved.

Glossary Adaptation Adjustment to changing conditions (including climate change); can refer to adjustment during the lifetime of an organism or system or to cross-generational genetic changes. Additionality The environmental impact, for example, emission reduction, achieved in comparison to a ‘business as usual’ development pathway. Agriculture, Forestry and Other Land Uses (AFOLU) Intergovernmental Panel on Climate Change guidelines for accounting of land-based greenhouse gas emissions (successor to the land use, land-use change, and forestry guidelines, but not yet formally accepted by United Nations framework convention on climate change (UNFCCC)). Clean Development Mechanism Part of the Kyoto accord of the UNFCCC

Introduction Perspectives on agricultural mitigation have evolved from the first report of the Intergovernmental Panel on Climate Change (IPCC) (Sauerbeck, 1993), through the second (Cole et al., 1996; Paustian et al., 1997), third, and fourth (Metz et al., 2007; Smith et al., 2008) to current discourse (Ericksen, 2008; Beddington et al., 2012; Burney et al., 2010; Vermeulen et al., 2012; Baker et al., 2012; Neufeldt et al., 2013). There has been (1) a refinement of numbers on current emissions and their sources, with agriculture currently responsible for 11% of global emissions (UNEP, 2013), (2) more integration in scenario modeling than cross sectoral borders (Golub et al., 2009), (3) responses to some of the accounting system anomalies that allowed global emission displacement around biofuels to be counted as emission reduction, (4) separate efforts to deal with forestry emissions under the REDD þ (efforts to reduce emissions from deforestation and forest degradation) agenda that showed the challenges of a partial approach in what is an integrated landscape (van Noordwijk et al., 2013), and (5) a greater appreciation of action opportunities on the demand side of the equation. Part of the food system industry is responding to consumer action and demand for low-carbon-footprint products, whereas formal governance systems and international negotiation arenas are slow to respond effectively. Current global greenhouse gas (GHG) emission levels are already considerably higher than would be allowed in 2020 in scenarios that keep global warming below a 2 1C target (UNEP, 2013). Experiments with carbon markets have captured the imagination beyond actual performance, but there certainly are considerable opportunities to reduce net GHG emissions while meeting rising global demands, compared to a ‘business as usual’ extrapolation of past trends. The challenge is how to provide economic incentives for ‘clean

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Intergovernmental Panel on Climate Change The science/policy boundary organization that reviews evidence on climate change in a 5-year cycle of reporting. Land use, land-use change and forestry Guidelines for accounting of land-based greenhouse gas emissions (superseded by AFOLU). Leakage The unintended effect on emissions elsewhere (beyond the project scale). Mitigation (in context of climate change) Reducing the net emissions of greenhouse gasses to the atmosphere. Value chain A representation of a sequence of actions that transform raw materials (or land use enhancing C sequestration) into marketable products (certified emission reduction) that an end user could buy.

development’ across scales, without a huge bureaucracy and network of intermediaries whose pay and transaction rents compete with real actions on the ground. This article starts with defining the scope of mitigation and agriculture, before reviewing current emission estimates of the three main GHGs involved – nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) – across the agricultural spectrum, and discuss how projected increases in demand from a growing and more wealthy global population can be reconciled with emission reduction in macro-level scenarios. Finally, this is followed by considering the experiments with micro-incentive systems currently under way. Although there is a wealth of studies and syntheses in the technical literature, the focus here will be on bridging the ‘supply’ and ‘demand’ side approaches to achieve the overall objective of the United Nations Framework Convention on Climate Change (UNFCC) (UNFCCC, 1992) as stated in its second article, to ‘stabilize GHG concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.’ As one would note, there are several weaving errors in the regulatory tapestry set up for achieving the UNFCCC objective, made up of a warp of countries, a weft of sectors, and shades of colors ranging from mitigation to adaptation and vulnerability. As will be discussed below, neither the terms ‘mitigation’ nor ‘agriculture’ as defining concepts are as clean and clearly separated from other aspects as it might appear.

Mitigation as Part of the Climate Change Discourse Mitigation Plus Adaptation The term mitigation originally meant softening, as it is derived from the Greek mitis¼ soft, rather than from the kiSwahili

Encyclopedia of Agriculture and Food Systems, Volume 2

doi:10.1016/B978-0-444-52512-3.00002-4

Climate Change: Agricultural Mitigation

miti¼ forest. It has obtained a specific meaning in the international climate change discourse: it has become shorthand for reducing the net emissions of GHGs to the atmosphere that are seen as the primary drivers of global climate change, because such climate change is considered a risk for humanity and the future of planet Earth as known. Mitigation was defined as the primary line of defense in the chain of events (Figure 1) that caused a reduced quality of life due to the human activities that induce an increase of atmospheric concentrations of GHGs. The atmospheric concentration of GHG's, net result of emissions and uptake by oceans and terrestrial systems, together with solar irradiation, reflection (albedo), and hydrological cycle shape the climate system; the current rate of change will soon bring us beyond the safe planetary boundaries of our coping range (Rockstrom et al., 2009). This will lead to direct human vulnerability and to indirect effects on human welfare through ecosystem changes. Adaptation is a second line of defense, which reduces vulnerability in the face of exposure to change, but which implies a failure of the UNFCCC to achieve its primary target. Adaptation shifts the concept of what is ‘dangerous,’ but does not reduce interference with the climate system. Nor can it deal with the risks of run-away, positive feedback loops such as changes in ocean current systems, inducing further change once thresholds are crossed. One does not know exactly where those thresholds are, so the precautionary principle should be applied (Ramanathan and Feng, 2008; Rockstrom et al., 2009). Early warning signs of real change have been around for at least two decades (Smith et al., 2009). Synergy between mitigation and adaptation is feasible in land use (Verchot et al., 2007; Smith and Olesen, 2010).

Direct Micro- and Meso Climate Forcings?

Exogenous variabiliy

Atmospheric concentrations of short- and long-lived greenhouse gasses

Human actions

Climate systems Impacts of actual and predicted climate change on human and ecosystems

Ot effe her p cts oten o t sys n clim ial tem ate s

Mitigation

Anthropogenic GHG emissions

Atmosphere

There is an alternative perspective to the conventional cause–effect-impact relationship between agriculture and climate. It does not solely or even primarily relate to the global GHG effects – as indicated a bypass to the macroclimatic GHG route (Figure 1). Pielke et al. (2007) discussed the diverse local and regional climate forcing that impact agricultural systems and represent effects of local land cover change and aerosol production on local climate and geographically explicit

Adaptation Human quality of life

Vulnerability

Figure 1 Feedback loop from human actions via GHG emissions to climate change, impacts on human and ecosystems and vulnerability and ultimately quality of life where these impacts exceed the coping range, potentially adjusted by adaptation measures.

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teleconnections, relationships between local effects and distant but geographically explicit causes. In their view, agricultural assessments of risk to climate change and variability should start with a bottom-up perspective of understanding local climate, as a complement to global top–down modeling. Actions to mitigate climate change may similarly be seen from a new angle if a coadapt approach is taken (van Noordwijk et al., 2011) that allows for local actions with local effects to add up to global impacts; tree effects on the microclimate of agriculture begin to get recognized (van Noordwijk et al., 2014c). New perspectives on ‘rainbow water’ that relate terrestrial evapotranspiration to rainfall elsewhere on the same continent showcase specific teleconnections (van Noordwijk et al., 2014a).

Accounting for Anthropogenic Emissions per Area, Activity, Capita, or Sector The concept of anthropogenic interference with climate systems is an aggregate that needs disaggregation before it can be dealt with. This is where the problem starts. The totality of emissions can be derived from summing over all people and their per capita emissions, from summing over all land areas and the change that occurs per unit of space or from summing over all sectors and subsystems of human activity: Anthropogenic interference ¼ f ðΣEGHG Þ ¼ f ðΣi EGHG,i Þ ¼ f ðΣj EGHG,j Þ ¼ f ðΣk EGHG,k Þ ¼ f ðΣn EGHG,n Þ þ M

½1

where i sums over all pixels (units of space) on planet Earth, j over all people and their per capita emissions and k over all sectors and types of human activity with associated footprints. The summation over all nations n requires an additional term M for the international waters and international transport that are not otherwise attributed. In principle, the first three approaches can all lead to a consistent result. However, what we currently have in the policy debate is a hybrid, which contains elements of all three (national emissions, per capita calculations, and product footprints), but is at risk of double-counting as well as having gaps. Although emissions are of primary interest, which are fluxes, there are good reasons to approach them through changes in directly observable stocks (e.g., carbon stored in soils or vegetation) for part of the accounting system, but again hybrids of flux and stock accounting are problematic. Linked to the United Nations framework in which the UNFCCC was developed, nation states are the primary accounting units. This implies primarily a territorial and citizen-based approach to accounting, but has challenges with multinational companies, international (cross-border) trade and is trapped in a political dichotomy of ‘developed’ versus ‘developing’ countries (diplomatically termed ‘Annex I’ vs. ‘Nonannex I’), where the major share of emissions shifted to transitional economies such as China (Peters et al., 2011). In absolute levels, developing (and transitional) countries accounted in 2010 for approximately 60% of global GHG emissions (UNEP, 2013). Davis and Caldeira (2010) estimated that 23% of global CO2 emissions (6.2 Pg CO2) were traded internationally, primarily as exports from emerging markets to consumers in developed countries. Sharing

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responsibility for emissions embodied in trade among producers and consumers could, in their view, facilitate international agreement on global climate policy – agreements now hindered by concerns over the regional and historical inequity of emissions. The emissions embodied in trade concept also applies to agriculture and associated global trade flows (Minang et al., 2010). For example, local nutrient cycles became global nutrient flows (van Noordwijk, 1999), with continued dependence on new inputs and associated GHG emissions.

Footprint Accounting In the face of the failure of the nation states to achieve convincing collective action at par with the challenge, a global citizen-based approach has emerged with attention on the ‘footprint’ of all goods and services that they use for their lifestyles and diets (Pandey et al., 2011; Peters, 2010). This follows from a simple disaggregation of the citizen based accounting system: f ðΣj EGHG,j Þ ¼ f ðΣs Σm Ps Lm,s Fm Þ

½2

where P is human population size per social stratum s, L is lifestyle and per capita use of goods and services for social stratum s, and F is the footprint or emissions per unit goods and services (indexed m). Controlling P is a politically sensitive and religiously contested domain for public policy, and investment in access to education for girls may well be the only widely supported long-term approach. There is a large current disparity between social strata in L and there are valid aspirations to increase the average under the heading of ‘development.’ That leaves F, or the efficiency with which goods and services are produced, as the primary degree of freedom. Increasing efficiency is a potential win-win solution in many environment/economic tradeoffs.

Territorial, Sectoral, and Demand-Based Interpretations of ‘Agriculture’ Turning now to agriculture, elements of all accounting approaches are seen coming together, with several challenges for transparent and comprehensive accountability. Agriculture uses land – but as a land use category it has a fuzzy boundary with ‘forestry’ (Watson et al., 2000), as well as with ‘wetlands.’ These three land uses are adjacent chapters in the Agriculture, Forestry and Other Land Uses accounting system designed by IPCC (2006). Agriculture uses inputs such as fertilizer and machinery, which are derived from mining and manufacturing industry, as well as fossil fuels for farm operations and transport of products. In a sectoral approach these need to be accounted in one, and only one sector. However, farm-level decisions about alternative approaches then have cross-sectoral consequences that require consistency of policies across the various sectors involved. Agriculture is the basis of a food supply systems, with considerable waste along the chain, as only a fraction of the food that is produced is consumed (Parfitt et al., 2010). What part of the food wasted is attributable to agriculture, what part not? Agriculture together with forestry provides a large share of

the fiber supply systems with textile, paper, and other applications that also have fossil fuel–based alternatives. Jointly the two are still the primary source of energy for a large share of the rural population, with options to substitute firewood, charcoal, and dried-manure by fossil fuel use. On the other side of the spectrum, agriculture- and forestry-based biofuels resubstitute for fossil fuel. Emission reduction in one ‘sector’ can be achieved by shifting product flows and associated emissions to another sector, without decreasing the anthropogenic interference with the climate systems. The sectoral map of the world has dotted lines as boundaries (Figure 2). Rigidity of concepts such as an agriculture concept that does not allow overlap with forestry, as in Food and Agriculture Organization databases, is thus seriously challenged to deal with trees outside forest and agroforestry as intermediate land use system (de Foresta et al., 2013). Rigidity implies considerable cost to the rationality of decisions based on them.

Multiple Perspectives Compared to the discussions on ‘Mitigation in Agriculture’ in the first IPCC report (Sauerbeck, 1993), the current discourse (Beddington et al., 2012) has brought greater recognition for the demand side, with attention to waste and lifestyle choices of human diets. It also acknowledges that there are planetary boundaries to ambitions for all to emulate the American dream and diet. Thus the current debate encompasses multiple aspects, accounting principles, and outstanding issues of agriculture (Table 1). There may be a general trend to move from an area-based emissions per unit of agricultural land, to efficiency/footprintbased concepts (emissions per unit end-user satisfaction with goods and services), but these still have an area-based component in the calculation. Consequently, it requires productivity data. A concept of ‘indirect land use change’ that has emerged in the biofuel debate (Plevin et al., 2010) applies to any new or existing crop and is a challenging one. To what degree can a new use of a crop be held accountable for the additional conversion of land into agriculture elsewhere in the world? Will the new use have left some of the original demand unmet? Is every parcel of land that once supplied a product for a certain type of use bound to keep going that forever? With such concepts we appear to be trapped in the rigidity of artificial accounting concepts and need to go back to the basics of the totality of anthropogenic interference with climate systems. All this leads to a hot debate about the optimum level of intensity of land use, in the face of the nonlinear relationship between inputs, emissions, and yield per unit area (Doré et al., 2011; Jackson et al., 2010, 2012; Matson et al., 2012). As intensification influences various aspects of the accounting system, optimization from a GHG perspective can only be done at national aggregated level. In terms of GHG accountability, a focus on imports rather than local food production is a very attractive choice at national level – similar to the transfer of high-emission industries to countries without emission reduction commitments. However, from an atmospheric impacts perspective, focus should be on reducing the total of net GHG emissions directly or indirectly associated with the sum total of global agricultural production.

Atmospheric concentrations of short- and long-lived greenhouse gasses

Geological eposits

Fossil fuel use: Industry, light, heating, and transport Cement production

Oceans

Waste

Wetlands

recycling

systems

Food supply

Ag. inputs

ply systems

energy sup-

Agricultural land use

Renewable

Planetary skin

Agriculture, forestry and other land uses Production forestry

Net oceanic C sink

N2O and CH4

Change in terrestrial carbon stocks

Other land uses

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Climate systems

Rural+Urban systems

Atmosphere

Climate Change: Agricultural Mitigation

Food and energy demand: Human population size and lifestyles/ diets and associated footprints

Figure 2 Agriculture as part of the anthropogenic GHG emissions: It relates not only to an important part of land use (interfacing with forests, wetlands, and oceans as basis for food supply systems, as well as energy supply systems), but also with direct energy consumption for agricultural inputs and transport, and with (missed opportunities) for waste recycling; ultimately agriculture responds to the shifts in demand, that are based on human population size multiplied with the goods and services required for lifestyles and diets, modified by the footprints per unit good and services.

Current Emission Estimates In 2008, agricultural production, including indirect emissions associated with land-cover change, contributed 80–86% of total food system emissions. This was 19–29% of global anthropogenic GHG emissions, releasing 9.8–16.9 Pg of carbon dioxide equivalent (CO2e) to the atmosphere (Vermeulen et al., 2012).

CO2, N2O, and CH4 Compared The ‘greenhouse effect’ impacts of nitrous oxide and methane can be expressed in carbon dioxide-equivalent quantities based on their global warming potential. This includes the direct heat trapping effect of the gasses as well as their expected residence times in the atmosphere. Conventionally, a hundred-year time frame is used in defining the default CO2e values per unit N2O and CH4 at 296 and 25, respectively, Evaluated over shorter time frames, the global warming effect of CH4 would be rated higher.

population size accounts for 70% or more of the variation in forest cover at national and subnational scales, with 80% of data within plus or minus 10% of the predicted forest cover. However, the emission consequences of this conversion differ by the carbon density of the natural forest and the specific pathway of change, which can be gradual or direct; but the net effect on CO2 emissions does not depend on the pathway taken. Yet, 46% of the agricultural lands have at least 10% tree cover (Zomer et al., 2009), and trees are compatible with agricultural production (de Foresta et al., 2013). Fortunately, simple approaches to quantifying the net carbon loss from change in tree cover are available (Hairiah et al., 2011), compatible with IPCC (2006) guidelines. Methods for other GHG emissions are also becoming simpler (Milne et al., 2013). The net emissions per unit agricultural product vary along the forest or tree cover transition curve (Rudel et al., 2009; Meyfroidt and Lambin, 2011), depending on the preceding land cover that was converted and on how far back in history the accountability rules apply.

Soil Carbon Transition Curves Forest-to-Agriculture Conversion Agriculture and the size of the human population have risen as a consequence of deforesting the earth to create farm land (Williams, 2006; Gibbs et al., 2010). The logarithm of human

Soil carbon stocks express a balance between organic inputs and their stepwise decomposition by soil biota. The stock (tC ha1) can be estimated as the sum over annual inputs (tC ha1 year1) multiplied with mean residence time (year)

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Climate Change: Agricultural Mitigation

Table 1

Multiple perspectives on agriculture in relation to mitigation issues

Perspective on agriculture

Accounting principle

Challenges

1. Agriculture as land use, modifying above- and belowground C stocks in comparison to forests and wetlands and increasing or decreasing methane emissions 2. Agriculture as transformer of solar energy þ CO2 þ water þ nutrients into usable organic matter þ waste þ N2O þ CH4 3. Extensive rangelands grading into natural ecosystems, as start of intensification 4. Relations with oceans, coastal and freshwater fisheries, aquaculture, and animal feed stocks

Area-based emission accounting as per AFOLU (or its predecessor LULUCF; for CO2 emissions this is primarily based on change in above- plus belowground stocks, for N2O and CH4 on summation of fluxes N2O emissions from agriculture are estimated as fraction of total fertilizer use

What about trees outside forest and agroforestry? What about anthropogenic reduction of natural (e.g., wetland) ecosystem emissions?

Accounting per unit livestock, CH4 emission profiles depending on feeding regimes

N-rich feeds reduce CH4 emissions per animal, but increase N2O emissions of the manure International waters remain outside of any accounting system

5. Agriculture as driver of transport and input industry 6. Agriculture as basis of food system value chains, responding to demand signals

7. Agriculture as potential basis for ‘bioenergy,’ recyclable ‘waste’

Productivity and CH4 þ N2O emissions are accounted separate from the nitrogen and phosphorus transfers from agriculture that influence them Transport emissions are accounted outside the agricultural sector Footprint concepts and efficiency of output in usable products per unit emissions. Nonutilized production as consequence of supply-demand mismatch is not handled separately Domestic use of biofuel or methane capture from waste recycling is accounted through its reduction of fossil fuel dependency Where international trade is involved and products cross borders, ad hoc footprint efficiency criteria apply to bioenergy feed stocks

similar to tree cover transition. Conversion into agriculture reduces annual inputs, as more of the carbon gets exported from the field with harvested products, whereas it reduces the mean residence time as tillage speeds up decomposition and mineralization. With a switch in management practice a soil carbon transition can be induced similar to the tree cover transition. Such transitions can also result from increased cropping frequency and associated root inputs to the soil (Minasny et al., 2011; van Noordwijk et al., 2014b).

Livestock Livestock is accountable for emissions both through the way feed is produced with consequences for changes in C stocks and N2O emissions and though methane emissions at the animal level that depend on feed quality (IPCC, 2006; Herrero et al., 2009, 2010). In the context of global land cover data, the handling of the transition from grazed dry forest to wooded savanna and to rangeland with trees is a challenge for consistency: with seminomadic and transhumance livestock systems being more easily accounted per head than per area grazed. Deforestation in the humid forest zone of Latin America has been historically dominated by extensive livestock production, whereas in Africa Trypanomosiasis prevented similar livestock systems, whereas in Asia the regional supply/ demand situation did not make such conversion attractive.

What about N2O emissions based on biological N2 fixation or organic fertilizer inputs?

Can locally produced biofuel, be counted as carbon neutral? Where does accountability of agricultural sector end and that of other parts of the food system take over?

Attempts have been made to include international wood trade into the system, and the same might apply to other organic exports, but this creates loopholes and inconsistencies

Rice Paddies Methane emissions by cultivated paddies or natural wetlands is the net result of methane production in the anaerobic zones of submerged soils by methanogens, and its oxidation into CO2 by methanotrophs in the aerobic zones of wetland soils and in upland soils (Le Mer and Roger, 2001). Net methane emissions can be approximately 10 mg CH4 m2 h1, whereas methane oxidation by aerobic upland soils (forests are most active) is two orders of magnitude less. Submersion and organic matter addition increase methane emissions. Intermittent drainage and utilization of the sulfate forms of N-fertilizers reduce CH4 emission (Le Mer and Roger, 2001). Conversely, the methane oxidation potential of upland soils is reduced by cultivation, especially by ammonium N-fertilizer application.

Peatland Use Globally, peatlands store more than half of total soil carbon. Both in the northern temperate and tropical zones peatlands are in agricultural use, with annual emissions per unit area that are a factor 100 or more above those on mineral soils. Peatland emissions derive from the use of fire in land clearing, the increased decomposition due to drainage and fertilization. Together these make the organic residues that took thousands of years to accumulate disappear in one or a few decades.

Climate Change: Agricultural Mitigation

Where natural and disturbed wetlands and peats emit methane, methane oxidizers become effective once the water table is below 30 cm of the soil surface. Conversion of tropical peatland for plantation crops such as oil palm has become a major issue Agus et al. (2013).

Projected Increases and Relevance of Demand-Side Adjustments Shifts in Diets and Lifestyles The recurrent debate on how a human population of 9 billion can be fed with sufficient and sufficiently nutritious food has different answers depending on the degree of freedom in dietary choice that is assumed for future generations (Nelson et al., 2010; Shindell et al., 2012). Poverty reduction and expansion of a middle class has large consequences for the composition of the human diet, and its associated emissions and waste (Beddington et al., 2012; Parfitt et al., 2010). The different dietary options to meet daily human needs have very different footprints in terms of carbon and other GHG emissions. Although there are broad patterns associated with product food groups and their trophic position, there can be a considerable ‘management swing potential’ (Davis et al., 2013) that differentiates the best from the worst management practice in the production of goods that are otherwise indistinguishable. For example, palm oil can be both the best and the worst vegetable oil in terms of carbon emissions per unit product, depending on whether it is grown on peat or mineral soil, and whether the deforestation history of the site is still attributed to the current plantation. This equally applies if such palm oil would be used as biofuel source, rather than for the food industry, but focus of the debate has been disproportionally on such potential biofuel use. Although a more vegetarian lifestyle and diet has substantial benefits in reducing footprints, its direct consumption of soybean, rather than via an animal stage in a food chain, does not release it from the issues around the soybean carbon footprint that are primarily attributable to direct and indirect land use change (van Middelaar et al., 2013)

Bioenergy on the Agricultural Accounting Plate? Within the UNFCCC accounting rules, one of the simplest ways to meet emission reduction obligations is to move highemission industries, such as agriculture, across the accounting border. As land-based products can be subsequently used as biofuel and reduce dependency on fossil fuels without a change of lifestyle or transportation systems, a very attractive pseudosolution became available to policy makers. Crutzen et al. (2008) pointed to this accounting anomaly in the case of biofuels, and there have been several attempts since to redress the issue. If a substantial part of global energy needs in the future are to be met by biofuel sources, the land required for agricultural production may double – which shows the level of challenge involved. Although there have been hyped expectations of miracle biofuel crops that can be highly productive on marginal

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soils without dependency on inputs, reality is otherwise, as many farmers have learned the hard way (Iiyama et al., 2012).

Technical Opportunities for Efficiency Gain Plus Emission Reduction Vermeulen et al. (2012) estimated agriculture's net GHG emissions along the food chain as:

• • • •

3.8–5.2% due to production of fertilizer, pesticides, and feed transport (mostly CO2). 40.8–55.7% due to direct emissions in production stage (mostly N2O and CH4). 23.9–43.8% due to indirect emissions and initial land conversion (mostly CO2). 10.2–16.7% due to postproduction processing, transport, and cooling (CO2, N2O, and CH4).

Opportunities to reduce emissions exist throughout the chain, with the direct and indirect emissions offering the largest reduction options. The author will first focus on the direct emissions.

Reducing the Temporary Excesses of Available Nitrogen that Allow for High N2O Emissions Mosier et al. (1998) and more recently Reay et al. (2012) found current N2O estimates to be reasonably consistent at the global scale between accounting for measured atmospheric change and known emission sources, but that a lack of direct measurements makes national and subnational estimates highly uncertain. Although continued intensification of existing lands is essential in meeting future needs (Matson et al., 2012; Zhu and Chen, 2002), increased nitrogen nutrition of crops is needed. However, options exist to achieve that without increasing nitrous oxide emissions by increased N uptake efficiency at the farm scale, although these require appreciation of spatial heterogeneity in fields currently managed as if they were homogeneous (van Noordwijk and Wadman, 1992; Gebbers and Adamchuk, 2010; Cao et al., 2012). Expanding the buffer zone between nutrient excess and deficiencies in access is crucial (van Noordwijk and Cadisch, 2002) and requires location-specific solutions to increase synchrony, synlocation, and buffering (Hillier et al., 2012). In the transition from a primarily nutrient-constrained agriculture (Giller et al., 2006), overshoot into excessive fertilizer use is likely and leads to situations where emission reduction by reducing N fertilizer use can both increase yields as well as economic returns from farms (Kahrl et al., 2010). For N-rich regions in China, 15% of N fertilizer can be saved without yield loss, by increased nutrient use efficiency, whereas in N-poor regions of the same country, additional N fertilizer use would benefit yield (Wang et al., 2011b; Yunju et al., 2012).

Reducing CH4 Emissions by Better Feeding Regimes of Ruminants Methane emissions from ruminants are a consequence of an excess of carbon over nitrogen in the digestive system, and

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Climate Change: Agricultural Mitigation

they can be controlled by a more nutritious diet. Livestock will also grow faster when well fed, and thus the CH4 emissions per unit production are reduced from both sides of the ratio (Herrero et al., 2009, 2010). For dairy cattle, the conversion of paddy rice to fodder grass production is economically attractive in certain areas; whereas cut-and-carry systems make livestock compatible with forest protection on slopes (Lusiana et al., 2012). The flipside of improved nutrition is an increase in N2O emissions from the N rich manure produced. On balance, however, intensification of livestock management can reduce emissions per unit livestock product – but an increased share of such products in the diet of a wealthier human population is increasing the human footprint. More radical solutions are to make more insect protein attractive for human consumption (van Huis, 2013).

Reducing CH4 Emissions by Less inundation of Rice-Fields Methane emissions from rice agroecosystems depend on the water regime, straw incorporation, and nitrogen fertilizer levels (Wang et al., 2012). Substantial methane emission reduction without negative yield effects is possible by careful timing of inundation periods, which also help in weed control, and dryland conditions (Green, 2013). Not only the water level, however, but also water flow within the field needs to be taken into account in methane reduction strategies (Rizzo et al., 2013).

Wiser Use of Peatlands As the collapse and subsidence of drained peat interacts with the water management, agricultural use that is compatible with a water table of approximately 30 cm can substantially reduce emissions although maintaining agricultural production. Banning the use of fire in peatland clearing is one of the most cost effective ways to reduce emissions, but a reorientation of agricultural intensification to mineral soils is highly desirable in a mitigation context. Peatland agroforestry options exist (Tata et al., 2013; Mulia et al., 2013) and are worthy of further exploration.

Better Waste Recycling Waste is a secondary resource. Organic material can be used for its energy content (by direct burning or in a methane digester producing biogas), for its role in protecting the soil during a surface decomposition process, or by incorporation into the soil enhancing soil organic matter formation. There are tradeoffs between these functions. If N-rich biomass is left on the surface, such as clippings from leguminous trees, N2O emissions can be high (Verchot et al., 2006), but it is an open debate how important aboveground residues are for soil carbon formation relative to root inputs in no-till agricultural systems. If not needed for surface protection, they might be harvested as fodder or for energy content without harm to longer term soil carbon storage. However, the smoke of manure or crop residues used as fuel tends to contain a high particulate matter content, which forms aerosols and has a direct impact on regional climates through particulates in

haze, as well as on global climates (Granier et al., 2011; Mahowald et al., 2011).

Increased Carbon Storage in Soils The third IPCC assessment identified increased soil C storage as the primary option for agriculture to directly contribute to climate change mitigation (Smith et al., 2008). Most of this change was expected to come from widespread adoption of conservation agriculture systems with reduced tillage. There is considerable debate, however, on the interpretation of the data available, especially where the relative distribution of crop roots and soil organic matter is influenced by a change in soil tillage (VandenBygaart and Angers, 2006). Assessment in the top 100 cm of the soil profile may show less effect than an assessment in the top 30 cm, whereas the most impressive changes in soil carbon are obtained in the top 5–10 cm (Stockmann et al., 2013). Soil carbon needs a long-term perspective, with most of current understanding based on the very few long-term experiments that have primarily been used to calibrate the dominant soil carbon models (Powlson et al., 2011). There is evidence, however, of a soil carbon transition curve as a side-effect of agricultural intensification (Minasny et al., 2011; Xu et al., 2011; Stockmann et al., 2013), but with specific attention to incentives, increments might be faster. On mineral soils, however, it requires many years of high organic matter inputs to increase the soil carbon content by 20 tC ha1. The case for recovery of soil carbon in overgrazed and degraded drylands is sufficiently strong to warrant action, as the areas involved are large (Wang et al., 2011a).

Increased Carbon Storage in Trees in the Agricultural Landscape Increments in aboveground soil C storage of 20 tC ha1 can be more easily achieved by incorporating trees into farming systems. If in a rotational system, trees are harvested when they reach a 40 tC ha1 stock level, the time-averaged C stock over the rotation length is approximately 20 tC ha1 (Hairiah et al., 2011). Double this amount is quite feasible, and aboveground gains in C stock are thus more easily made than belowground ones. Given the prominence of trees outside forest and trees spread in agricultural landscapes (de Foresta et al., 2013; Zomer et al., 2009), a reassessment of the relative importance of tree versus soil carbon-based strategies from the third IPCC assessment report (Smith et al., 2008) may be needed (Aertsens et al., 2013; Mbow et al., 2014). Trees moreover have many direct impacts on local climates, including their roles as windbreaks and as providers of topsoil moisture during periods of water stress (Bayala et al., 2008). They are a key element in the bypass loop from human activity to climatic conditions influencing people (Figure 1), outside of the formal reach of ‘mitigation’ as understood in UNFCCC, but well aligned with local knowledge and perceptions (van Noordwijk et al., 2011; van Noordwijk et al., 2014c). Many trees additionally produce food and nonfood products, which have income and livelihood benefits for the local population (Leakey, 2012; Mbow et al., 2014).

Climate Change: Agricultural Mitigation

Indirect Emissions, Emission Displacement, and Macrosolutions As indicated, summaries such as Vermeulen et al. (2012) see land use change and the conversion of land to agriculture as a large component of current agricultural emissions. This implies that obtaining higher yields from existing agricultural lands, even if it increases area-based emissions, may be an overall mitigation strategy (Lambin, 2012). If instead of a global a national perspective is taken, however, the issue of indirect emissions is missing from the current accounting systems. If, however, indirect emissions are introduced into product-based footprint calculations, the outcome is controversial. Historically, many countries have been able to transit out of an economic dependence on primary agricultural production, with positive consequences for their forest area and tree cover. Part of the forest recovery is the consequence of the pull of rural populations toward urban and industrial areas elsewhere. Part is also due to the push for labor-extensive, profitable tree production systems, once the opportunities for essentially free harvest from natural forests are gone. However, as analyzed by Meyfroidt and Lambin (2009, 2011), countries that reported an increase in forest, such as Vietnam, have generally achieved this by increasing their external footprint. On an area basis, half the gain in forest cover is offset by expansion elsewhere. Where indirect land use change emissions are included in a product-based footprint, all producers of the same crop are supposed to have a joint responsibility on how production is managed. This goes substantially beyond the responsibility of a land manager for the specific conditions under which she/he produces the crop, in the upper or lower part of the management swing potential (Davis et al., 2013). Inclusion of indirect land use change in the rules thus has consequences for the possible incentive systems to achieve agricultural mitigation by reducing the footprint of the marketed products and reducing the net emissions from the total agricultural area while increasing total yields.

Carbon Markets and Other Experiments with Micro-Incentive Systems In response to consumer concerns, the food and agricultural processing industry has learned to respond to environmental concerns, including those on carbon footprints. Where the swing potential is large, as in the case of palm oil, the part of the food industry that targets markets with critical consumers (especially in European markets), it is keen to get associated with the upper segment of the swing potential, by creating voluntary standards of good performance. The Round Table on Sustainable Palm Oil (RSPO) has been pioneering this approach, but similar initiatives exist on other commodities. It is unclear, however, at what scale and time frame such efforts contribute to global mitigation, as substantial emission displacement can occur through a switch of the production in the lower segment of the swing potential to markets that are not accountable and not interested (e.g., palm oil export to other Asian countries).

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A major challenge in incentive systems, such as a carbon market, is whether it can provide investment in a shift to other development trajectories that can become financially sustainable on their own, or whether it only implies offsetting opportunity costs and will have to be continued, as a form of payment for environmental services (PES) for an indefinite period of time (van Noordwijk et al., 2012). The EU AgriEnvironment scheme, as one of the largest such efforts to support public policies in the rural landscape, has tried to introduce more conditionality of payment against environmental performance, including a requirement of increase in soil C content, but there are strong countervailing forces. There are many issues with economic incentives for agricultural mitigation (Table 2), operating in different policy domains, and with different challenges of achieving additionality (environmental performance above baseline) and avoiding leakage (negative environmental effects outside the primary accountability domain).

Closing Remarks There is a probability that current efforts to achieve mitigation have actually made things worse. Franks and Hadingham (2012) gave examples how a farm-focused effort at emission reduction in selected countries can lead to increases rather than decreases of global emissions. Henders and Ostwald (2012) in their overview of leakage in a forest context, also included relations with agricultural land use. Two decades of international climate negotiations to effectively implement the agreed framework convention, dealing with the additionality and leakage issues, have made very little progress. There may be some progress in bridging current debates on REDD þ and Nationally Appropriate Mitigation Actions in developing countries, but we are far from a Reducing Emissions from All Land Uses ideal. The dominant focus of the UNFCCC framing of the climate problem on GHG emissions is under scrutiny, with consequences for the way mitigation is perceived, especially in the land use sector. Firstly, there is growing recognition of the Faustian choice that derives from the net effect of air pollution on a global cooling, masking 50% of the committed GHG warming from the Industrial Revolution (Unger, 2012). Aligned with that view, is the enhanced visibility of global climate change after industrial sulfur dioxide emissions were reduced. Aggressive reduction of air pollutants, including fine particulate matter from biomass burning that causes haze, would increase climate warming (Jacobson, 2004; Lamarque et al., 2010). Within the air pollutants, however, methane through its effect on ozone decay (Fiore et al., 2008), is a candidate for selective reductions in warming air pollutants, which may provide a way to mitigate near-term warming by complete pollution control until CO2 reductions take effect (Unger, 2012). Worldwide implementation of current CH4 emission control technologies in waste management, agriculture, and the extraction and transport of fossil fuels by 2030 would lead to a reduction in anthropogenic CH4 emissions of 24% (relative to 2010 levels) and decrease the global mean warming by an estimated central range of 0.2–0.4 1C relative to a business-as-usual scenario (Unger, 2012).

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Table 2

Climate Change: Agricultural Mitigation

Incentive systems for achieving agricultural mitigation

Accounting principle

Economic incentives to mitigate net greenhouse gas emissions from agriculture

Additionality

Leakage

Area-based (Annex-I countries)

National (or European Union-level) emission reduction commitments translate into incentive systems to reduce agricultural emissions, and into formal carbon markets that might in future allow agricultural emission reduction credits to be exchanged for fossil fuel emission permits; the carbon market in Europe is currently restricted to fossil-fuel emission rights Voluntary action to reduce emissions, often project-based; naming and shaming of export-oriented agriculture with high emissions leads to shifts in behavior; in North America, outside of Kyoto protocol and its compliance rules, carbon markets have emerged that support a shift to conservation agriculture for its C storage effects Consumer choice for products with lower footprint, often supported by forms of ecocertification and industry selfregulation, allows some linkage between consumers and producers, but is challenged by indirect emission concepts as it can cherry-pick the cleanest part of production systems without impact on the sector as a whole

Currently, agricultural mitigation is a cobenefit from other actions to make agricultural landscapes multifunctional and make agriculture sustainable

As international agreements do not yet include the land use sector, leakage is not a big risk

A/R-CDM rules for additionality have been simplified for smallscale projects, but still are not widely used; voluntary carbon market standards such as VCS support well-intentioned action, limited in scope and reach

Leakage risk in restoration is small; leakage has been the primary challenge for protection of C stocks in REDD þ , and require accountability at national scale

If footprints calculations would cover all activities and value chains, a real reduction in environmental impacts per capita may be expected

Indirect land use change represents ‘leakage,’ but is controversial in its application

Area-based (outside of Annex-I countries)

Product-based (footprint and efficiency criteria)

Abbreviations: A/R-CDM, afforestation and reforestation as part of the clean development mechanism; REDD+, efforts to reduce emissions from deforestation and forest degradation; VCS, voluntary carbon schemes.

Second, non-GHG influences of land cover and land use on rainfall, windspeed, maximum daily temperature, and other aspects of climate fall technically outside of the remit of the mitigation agenda. However, they may well have been underestimated in the public and policy discourse on climate modification that became overly carbon-centric. Third, and sadly, public discourse remains interested in oxygen supply by plants, rather than the carbon balance and GHG effects, even though this is a nonissue in any place other than a space capsule (van Noordwijk and Lusiana, 2013). Franks and Hadingham (2012) concluded that auditing methodology of the Kyoto Protocol is at fault. They suggest that a consumption, rather than a territorial/production, approach could be more effective, especially if it includes GHG emissions that are a consequence of farmer's decisions including overseas land use change. However, current life-cycle accounting is often still partial; allowing the term waste to be used. Waste is a wasteful concept, without specifying how and where it returns to global cycles of nutrients (and other elements), and links to energy/entropy flows. The current deficiency in recycling/reuse has multiple rationales, but it partly represents major progress in public health in breaking the life cycle of human parasites and causal agents of diseases. Closing the urban–rural loop in food production, consumption, and

waste management would represent real and lasting agricultural mitigation.

See also: Agroforestry: Complex Multistrata Agriculture. Agroforestry: Fertilizer Trees. Agroforestry: Fodder Trees. Agroforestry: Hydrological Impacts. Agroforestry: Practices and Systems. Agroforestry: Participatory Domestication of Trees. Biodiversity and Ecosystem Services in Agroecosystems. Biodiversity: Conserving Biodiversity in Agroecosystems. Ecoagriculture: Integrated Landscape Management for People, Food, and Nature. Food Security: Yield Gap. Soil: Nutrient Cycling

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Climate Change: Agricultural Mitigation

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Relevant Websites http://www.asb.cgiar.org/ ASB (Alternatives to Shash and Burn Partnership for the Tropical Forest Margins). http://ccafs.cgiar.org/ CCAFS (Climate Change, Agriculture and Food Systems). http://www.climatesmartagriculture.org/en/ Climate Smart Agriculture. http://www.ecoagriculture.org/ Ecoagriculture.

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http://www.es-partnership.org/esp ESP (Ecosystem Services Partnership). http://www.fao.org/climatechange/climatesmart/en/ FAO Climate Smart Agriculture. http://www.cgiar.org/our-research/cgiar-research-programs/cgiar-research-programon-forests-trees-and-agroforestry/ FTA (Forests, trees and Agroforestry). http://www.soilcarbon.org.uk/ Global Benefits of Soil carbon (SCOPE). http://www.scopenvironment.org/ SCOPE (Scientific Committee on Problems of the Environment). http://www.unep.org/ UNEP.