# Aligning agriculture and climate policy

Abad Chabbi, J. Lehmann, Philippe Ciais, Henry William Loescher, Maria Francesca Cotrufo, A. Don, M. Sanclements, L. Schipper, J. Six, P. Smith, et al.

► To cite this version:

Abad Chabbi, J. Lehmann, Philippe Ciais, Henry William Loescher, Maria Francesca Cotrufo, et al. Aligning agriculture and climate policy. Nature Climate Change, 2017, 7 (5), pp.307-309. 10.1038/nclimate3286. hal-01536008

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COMMENTARY:

# Aligning agriculture and climate policy

A. Chabbi, J. Lehmann, P. Ciais, H. W. Loescher, M. F. Cotrufo, A. Don, M. SanClements, L. Schipper, J. Six, P. Smith and C. Rumpel

The 4‰ initiative to sequester carbon in soils has the potential to connect sustainable development goals, enhance food security and mitigate climate change by utilizing waste organic residues.

Our climate is changing with potentially severe implications for human life if we are not able to limit the global average temperature increase to below 2 °C. Global models indicate that this target can only be met in the long term with negative emissions¹, that is, carbon removal from the atmosphere. It has long been suggested that carbon sequestration in soils may be a significant climate mitigation wedge². Although much research has been devoted to increasing organic carbon (OC) sequestration by managing soils, it has not been part of negotiations for the United Nations Framework Convention on Climate Change. However, ahead of COP21, a voluntary action plan was proposed, which included the 4‰ initiative (www.4p1000.org), focusing on soil OC (SOC) sequestration to mitigate climate change and improve food security. Since then, public awareness of soils as C sinks has grown and the possibility of effectively counterbalancing anthropogenic emissions by increasing the OC content of soils has become an attractive alternative to other climate mitigation measures due to its numerous co-benefits. The soils of cultivated ecosystems may serve this purpose because they are already managed for food production, because they present opportunities for restoring SOC stocks due to historical losses, and because organic residues from various sources, often considered as a waste, could be used to build SOC.

Here we discuss the specific road map, implications, expected benefits and limitations of this initiative. We suggest a strategy to increase SOC sequestration by increasing C-use efficiency across sectors and itemize concrete scientific, socio-economic and political strategies to achieve this aim.

## Connecting development goals

The 4‰ initiative is part of the Lima Paris Action Agenda and is supported by the United Nations Food and Agriculture Organization. Its goal is to increase SOC annually by 4‰ of its current stock through the implementation of economically viable and environmentally sound agronomic practices. If these practices were applied to all global soils, it would amount to a net CO₂ removal of 6 Gt C y⁻¹ from the atmosphere, which would offset two-thirds of the annual anthropogenic CO₂ emissions (Table 1). Since not all global soils are managed, an achievable potential is more likely to be limited to ~1 Gt OC y⁻¹ (ref. 3). This is, nevertheless, substantial and would offset the fossil-fuel emissions equivalent to those of a large emitter such as the European Union.

Moreover, increasing SOC storage, as proposed by the 4‰ initiative, is important for restoring agricultural soil quality, which has declined under intensive agricultural

management. Indeed, high demand on soils for food production has led to SOC loss over the past century. When SOC is lost, soils become prone to erosion and may no longer be able to fulfil their multiple functions. The primary function of agricultural soils is food production, but they are increasingly used for provision of a range of other ecosystem services⁴ at the nexus of agriculture, energy and environmental protection. Increasing SOC storage, as proposed by the 4‰ initiative, is thus crucial for restoring agricultural soil quality, and is also in the interest of landowners. Increased SOC storage may improve farmers' income through enhanced soil productivity, lower fertilizer requirements and sustained yields⁵. However, at present, these additional benefits to farmers remain largely unquantified.

Tackling national and global food security issues and climate policy together has strong political appeal and applies science to societal needs. The 4‰ initiative is a concrete example

<table><caption>**Table 1 | Mass balance of the global stocks and fluxes to and from the atmosphere to elucidate the 2004–2014 data.**</caption><thead><tr><th colspan="2">Carbon stocks and fluxes</th></tr></thead><tbody><tr><td>Atmospheric C stock* (Gt)</td><td>414</td></tr><tr><td>Top soil (0–0.3 m) organic C stock* (Gt)</td><td>690 ± 90</td></tr><tr><td>Total soil (0–0.4 m) organic C stock* (Gt)</td><td>860</td></tr><tr><td>Total soil (0–1 m) organic C stock* (Gt)</td><td>1,500 ± 230</td></tr><tr><td>Proposed 4‰ of total soil (0–1 m) organic C stock (Gt)</td><td>6.0 ± 0.92</td></tr><tr><td>Annual fossil-carbon emissions (flux to atmosphere)† (Gt y⁻¹)</td><td>9.8</td></tr><tr><td>Annual land use change C emissions (flux to atmosphere)† (Gt y⁻¹)</td><td>0.9</td></tr><tr><td>Annual net land C sink (2005–2014)*,† (Gt y⁻¹)</td><td>-3.2</td></tr><tr><td>Annual net ocean C sink (2005–2014)*,† (Gt y⁻¹)</td><td>-2.7</td></tr><tr><td>Rate of increase of atmosphere C (2005–2014)* (Gt y⁻¹)</td><td>4.7</td></tr></tbody></table>

A negative sign indicates a flux from the atmosphere to the biosphere; ± values denote 1 s.d; units are given in brackets. *Does not include permafrost¹⁴; †GCP 2014, only includes CO₂ sources, does not include non-CO₂ sources of greenhouse gas emissions¹⁵; ‡http://go.nature.com/2nTK1oA and http://go.nature.com/2oVQyyC
<figure><img src="image_2.png" /><figcaption>**Figure 1** | Conceptual diagram depicting C flow in a system with C-use optimization among sectors. In such a system, organic wastes are transformed into soil amendments.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>**Figure 2** | Societal benefits gained from soil carbon sequestration.</figcaption></figure>

of connecting the priorities of the sustainable development goals.

### Improving OC flow connectivity

In addition to improved agricultural management, intensification of organic residue recycling as part of a circular economy may be a promising strategy for increasing SOC sequestration. Transformation of such waste materials is intended to generate organic amendments ready for agricultural use⁶. This requires improving the connectivity between organic residue production and transformation systems and needs to take into account the associated nutrient budgets. Moreover, site-resolved and time-resolved solutions have to be developed. Improvement in the C-use efficiency should bring together different socio-economic sectors, to identify:

* The most suitable soils to receive and store SOC, for example, soils which have been historically depleted, or those with mineralogical and physical properties favourable for SOC retention⁷.

* Sources of organic wastes and their suitability.

* Appropriate, site-specific transformation strategies, including composting, pyrolysis and hydrothermal carbonization.

In a nutshell, we argue that the critical path of the 4‰ roadmap is to ameliorate OC (and nutrient) use efficiency to channel organic waste to soil pools, across sectors (Fig. 1), taking into account regional and societal differences in different parts of the world. This approach would greatly benefit from merging the development of digital agriculture and smart grids for energy and carbon. From a global perspective, across sectors, the effective implementation of organic waste recycling under the 4‰ initiative would benefit from improvement of the connectivity of organic matter flows. Organic matter use should be as diverse as possible and as long as possible before C returns to the atmosphere as CO₂.

### Economic co-benefits and trade-offs

There are strong competing economic interests for the use of land and organic matter, for example, for biofuels¹¹ or for other purposes, such as livestock, home heating, and cooking. The important value of the 4‰

initiative is to broaden the view to multi-purpose beneficial soil management systems that take into account the various ecosystem services of productive, healthy soils with enhanced SOC content. However, while it is generally considered that SOC provides these services, this is not always the case⁸. There is a paucity of information demonstrating the benefits of increasing SOC across a range of different soils, agro-ecosystems and climatic zones. Here, scientific meta-analysis, data harmonization, improved data sharing and access as well as spatially-explicit data-driven and user-friendly modelling alongside large-scale experimentation (for example, http://www.anaee.com) would greatly facilitate the decision-making process about the real economic return of adding OC to cultivated soils.

The momentum derived from the 4‰ initiative shows rare political will. But political willingness itself will only make the 4‰ initiative effective for large-scale removal of CO₂ if it is accompanied by substantial social and economic investment, for example, by the rehabilitation of degraded soils. About 24% of the world's arable soils are degraded⁹, and increasing their OC stocks is required for their rehabilitation. Degraded soils also have the largest potential for improving soil functionality through OC addition. One practical way to help reach the 4‰ goal is thus to demonstrate the quantitative co-benefits of SOC and their economic value to land owners, for conditions close to those they experience every day.

### Balancing social priorities globally

Adoption of adequate management practices, as well as exogenous organic matter inputs, may face conflicting priorities concerning sustainable development goals in tropical and temperate regions. For example, while enhancing food production is still the major goal in many tropical countries, environmental protection policies may be of higher concern in temperate areas, where food supply is more secure. While social acceptance and legislation for use of transformed organic waste materials to increase SOC are necessary in temperate countries, resource availability and economic competition with other uses of organic wastes (for example, as a fuel, building material, or animal feed) may be a barrier in many tropical countries. Such utilization of local waste has short-term economic return compared to the long-term benefits of SOC sequestration.

In less-developed countries, the societal impact of adopting the 4‰ goals is likely to be much greater through improved food production than in countries with intensive agriculture. Food insecurity has been identified as a driver of conflicts¹⁰ and migration¹¹. Increasing soil fertility and food
production in less-developed countries, to which SOC sequestration can significantly contribute, addresses inequity issues and global geopolitical challenges (Fig. 2). Therefore, for the first time, interests of developed and developing countries merge through the common objective to increase SOC contents.

## The way forward

The 4‰ initiative was proposed as one approach to offset current CO₂ emissions, while contributing to food security and a healthier environment. Compared to other climate mitigation measures, the science basis to increase SOC stocks and to measure the effectiveness of C sequestration is mature. The basic processes leading to SOC sequestration have been identified¹² as have the management practices to be implemented¹³. Implementation of SOC storage under the 4‰ initiative is feasible even in developing countries, because it does not require new technological breakthroughs. Since SOC storage can be practiced on current agricultural land and grassland, it does not take land out of agricultural production, as is the case for, for example, afforestation.

However, there are scientific, political, and socio-economical issues with its large-scale implementation. We need to identify soils and agro-ecosystems most suitable to increase SOC sequestration and quantify the economic benefits of additional C storage for different soil types, climate zones, production systems and farming capabilities, beyond C credits. The connectivity of C flows across sectors needs to be assessed and optimized to maximize environmental and socio-economic benefits, before CO₂ is released back to the atmosphere. Detailed region-specific

implementation options will have to be established to build concrete success stories. And finally, the implementation success of the 4‰ initiative will depend on our ability to improve global governance and regional collaboration between actors and across sectors, and to communicate the benefits of SOC sequestration through the consumer supply chain.

A. Chabbi¹,²*, J. Lehmann³, P. Ciais⁴, H. W. Loescher⁵,⁶, M. F. Cotrufo², A. Don⁸, M. SanClements⁵,⁶, L. Schipper⁹, J. Six¹⁰, P. Smith¹¹ and C. Rumpel¹²* are at ¹Institut National de la Recherche Agronomique, URP3F, 86600 Lusignan, France. ²Institut National de la Recherche Agronomique (INRA), UMR Ecologie Fonctionnelle et Ecotoxicologie des Agroécosystèmes (Ecosys) Bâtiment EGER, Campus AgroParisTech Grignon 78850 Thivalver Grignon, France. ³Soil and Crop Sciences, Cornell University, Bradfield Hall, Ithaca, New York 14853, USA. ⁴Laboratoire des Sciences du Climat et de l'Environnement, LSCE, F-91191, Gif sur Yvette, France. ⁵Battelle-National Ecological Observatory Network, 1685 38th Street, Boulder, Colorado 80301, USA. ⁶Institute of Alpine and Arctic Research (INSTAAR), University of Colorado, Boulder, Colorado 80301, USA.

⁷Department of Soil and Crop Sciences, Colorado State University, 200 W. Lake Street, Fort Collins, Colorado 80523, USA. ⁸Thünen-Institute Climate-Smart Agriculture, Bundesallee 50, 38116 Braunschweig, Germany. ⁹Faculty of Science and Engineering University of Waikato, Hamilton 3240, New Zealand.

¹⁰Department of Environmental Systems Science, Swiss Federal Institute of Technology, ETH Zurich, 8092 Zurich, Switzerland. ¹¹Institute of Biological and Environmental Sciences, University of Aberdeen, 23 St Machar Drive, Aberdeen AB24 3UU, UK. ¹²CNRS, Institute of Ecology and Environmental Sciences Paris, 78850 Thivalver-Grignon, France.

*e-mail: abad.chabbi@inra.fr; cornelia.rumpel@inra.fr

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## Acknowledgements

This work was supported by and benefited from the European Commission through FP7 projects, Distributed Infrastructure for Experimentation in Ecosystem Research (ExpeER) grant agreement number 262060 and Analysis and Experimentation in Ecosystems (AnaEE) grant agreement number 312690, and the CLAND Convergence Institute funded by ANR. The input of P.S. contributes to U-GRASS (grant number NE/M016900/1) and the Belmont Forum/FACCE-JPI DEVIL project (grant number NE/M021327/1). C.R. received funding from INSU/CNRS (Lombicom project) and ADEME (Vermisol project) and from ANR (MOSAIK, grant agreement no: ANR-12-AGRO-0005). Contributions from L.S. and A.C. were supported by GPLER, contract number SOW12-GPLER-LCR-PM. H.W.L. and M.S.C. acknowledge the National Science Foundation for ongoing support of NEON. The manuscript contributes toward results of the ARC discovery grant ‘Carbon Conundrum’ (DP140100323).

## Author contributions

A.C. initiated the writing of the paper and led the work. C.R. wrote the first version of the manuscript and prepared the figures. All authors contributed with ideas, and participated in the writing of the paper.

## COMMENTARY:

# Out of the lab and into the field

### Dan M. Kahan and Katherine Carpenter

Decision scientists have identified remedies for various cognitive biases that distort climate-change risk perceptions. Researchers must now use the same empirical methods to identify strategies for reproducing — in the tumult of the real world — results forged in the tranquillity of their labs.

For nearly as long as science has known that humans are responsible for significant global warming, decision scientists have been furiously engaged in research to promote constructive public engagement with this

threat¹. The ineffectuality of their efforts is painfully inscribed in polls that document the immobility of public opinion over time², not to mention the most recent US presidential campaign, which resulted in the victory of a

candidate who has declared climate change a hoax.

Why hasn't the new 'science of science communication'³,⁴ achieved more? A large part of the problem has to do with where decision